Re: 3D visualizations in Python

[marco . nawijn]

On Tuesday, March 12, 2019 at 11:54:22 PM UTC+1, Jakub Bista wrote:
> Hello. I want to do 3D visualization in Python. Which framework do you 
> recommend me for creating such a Interface?

I would recommend the VTK library (https://vtk.org/). It has excellent Python 
bindings. 

Marco
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Re: subprocess : AttributeError: 'Popen' object has no attribute 'read'

[marco . nawijn]

On Thursday, January 3, 2019 at 9:40:43 PM UTC+1, Chris Angelico wrote:
> On Fri, Jan 4, 2019 at 7:37 AM Mohan Mohta  wrote:
> > I am no expert in python but I found grep is lot faster in than the methods 
> > of reading files from python point me to direction if you know of 
> > anything faster I would appreciate it.
> >
> 
> Try doing things the simple and easy way in Python, then figure out if
> it's too slow. Only THEN should you worry about "faster".
> 
> ChrisA

Yeah, and once you find out you need to go faster and subsequently start 
looking into ways you *can* go faster, you finally end up with code similar to 
what is implemented in the grep family of tools.

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Re: Python-remove duplicate output

[marco . nawijn]

On Thursday, November 22, 2018 at 12:10:28 AM UTC+1, drvuc...@gmail.com wrote:
> How to remove duplicate lines and store output into one ine
> 
>reservations = ec.describe_instances().get('Reservations', []) 
> 
>for reservation in reservations:
> for instance in reservation['Instances']:
> tags = {}
> for tag in instance['Tags']:
> tags[tag['Key']] = tag['Value']
> if tag['Key'] == 'Name':
> name=tag['Value']
> 
> if not 'Owner' in tags or tags['Owner']=='unknown' or 
> tags['Owner']=='Unknown':
> print name
> 
> Current Output:
> 
> aws-opsworks
> 
> aws-opsworks Ansible
> 
> Desired output:
> 
> aws-opsworks Ansible

You can use a set to do the job. Remember that members in the set are unique,
duplicate members are ignored.

Before you start the for loop, create a set:

names = set()

Instead of `print name`, you add the name to the set:

names.add(name)

Note that if name already exists, because members of a set are unique, 
the name is (at least conceptually) ignored.

Once the for loop is completed, you print the remaining names.

print names (Python 2)
or
print(names) (Python 3)

Marco
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Re: question on the 'calendar' function

[marco . nawijn]

On Tuesday, November 20, 2018 at 7:53:06 PM UTC+1, o1bigtenor wrote:
> On Tue, Nov 20, 2018 at 11:50 AM Schachner, Joseph
>  wrote:
> >
> > It's possible I don't understand the question.  The calendar functions are 
> > NOT limited to this year or any limited range.
> >
> > Example:
> > import calendar
> > print( calendar.monthcalendar(2022, 12) )
> >
> > Prints lists of dates in each week of December 2022.  It prints:
> > [[0, 0, 0, 1, 2, 3, 4], [5, 6, 7, 8, 9, 10, 11], [12, 13, 14, 15, 16, 17, 
> > 18], [19, 20, 21, 22, 23, 24, 25], [26, 27, 28, 29, 30, 31, 0]]
> >
> > So, Dec 1 is a Wednesday; Dec 31 is a Saturday.
> >
> > That's 49 months ahead of this month.   Change the year and month to any 
> > (valid) number, and it will do what it does.
> > The only caveat is that if the moon's orbit slows down as it gets farther 
> > away from the earth and the earth's rotation speed changes, then the 
> > calculations done by calendar for leap years may not be correct about the 
> > distant future.
> >
> 
> Greetings
> 
> If my syntax or commands are wrong - - - - I've just started so
> something is likely to NOT be correct - - - grin - - - I'sa noob!
> 
> # calendar 2019
> 
> that is to show the year 2019
> 
> How could I show June 2018 to Dec 2019, inclusive?
> Or June 2018 to Dec 2021, inclusive?
> Or June 2018 to Dec 2023 by week (June wk 1,2,3,4 2018; July wk
> 1,2,3,4,5 2018; . . .   Dec wk 1,2,3,4,5 2023 or maybe even by dates),
> inclusive?
> 
> Note that the time frame is ALWAYS more than 1 year.
> AIUI there isn't a way to do that, at least not that I can see, and I
> would like to be able to do that.
> A friend suggested using a script wrapped around the command. I
> thought maybe there might we a way of doing what I need to do without
> using 2 levels of programming.
> 
> Regards

>From what you post it seems like you are on a Linux kind of system and you are 
>running the `calendar` command in the bash terminal. If that is correct, try 
>the following:

In the bash terminal type (without the literal #):
# python 

This will put you in the Python prompt (marked with >>>).
Check that the first line starts with Python 3. If not, I highly recommend
you install Python 3. If it is Python two, the following will work, but you
have to drop the outer parentheses for print (thus print calendar.calendar()) 

Then type the following:
>>> import calendar
>>> print(calendar.calendar(2020))

This will show:
  2020

  January   February   March
Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su
   1  2  3  4  5  1  2 1
 6  7  8  9 10 11 12   3  4  5  6  7  8  9   2  3  4  5  6  7  8
13 14 15 16 17 18 19  10 11 12 13 14 15 16   9 10 11 12 13 14 15
20 21 22 23 24 25 26  17 18 19 20 21 22 23  16 17 18 19 20 21 22
27 28 29 30 3124 25 26 27 28 29 23 24 25 26 27 28 29
30 31

   April  May   June
Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su
   1  2  3  4  5   1  2  3   1  2  3  4  5  6  7
 6  7  8  9 10 11 12   4  5  6  7  8  9 10   8  9 10 11 12 13 14
13 14 15 16 17 18 19  11 12 13 14 15 16 17  15 16 17 18 19 20 21
20 21 22 23 24 25 26  18 19 20 21 22 23 24  22 23 24 25 26 27 28
27 28 29 30   25 26 27 28 29 30 31  29 30

July August  September
Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su
   1  2  3  4  5  1  2  1  2  3  4  5  6
 6  7  8  9 10 11 12   3  4  5  6  7  8  9   7  8  9 10 11 12 13
13 14 15 16 17 18 19  10 11 12 13 14 15 16  14 15 16 17 18 19 20
20 21 22 23 24 25 26  17 18 19 20 21 22 23  21 22 23 24 25 26 27
27 28 29 30 3124 25 26 27 28 29 30  28 29 30
  31

  October   November  December
Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su  Mo Tu We Th Fr Sa Su
  1  2  3  4 1  1  2  3  4  5  6
 5  6  7  8  9 10 11   2  3  4  5  6  7  8   7  8  9 10 11 12 13
12 13 14 15 16 17 18   9 10 11 12 13 14 15  14 15 16 17 18 19 20
19 20 21 22 23 24 25  16 17 18 19 20 21 22  21 22 23 24 25 26 27
26 27 28 29 30 31 23 24 25 26 27 28 29  28 29 30 31
  30

Now look at the documentation of the calendar module to find out about
other options.

Marco
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Re: Is there are good DRY fix for this painful design pattern?

[marco . nawijn]

On Monday, February 26, 2018 at 3:44:14 PM UTC+1, Steven D'Aprano wrote:
> I have a class with a large number of parameters (about ten) assigned in 
> `__init__`. The class then has a number of methods which accept 
> *optional* arguments with the same names as the constructor/initialiser 
> parameters. If those arguments are None, the defaults are taken from the 
> instance attributes.
> 
> An example might be something like this:
> 
> 
> class Foo:
> def __init__(self, bashful, doc, dopey, grumpy, 
>happy, sleepy, sneezy):
> self.bashful = bashful  # etc
> 
> def spam(self, bashful=None, doc=None, dopey=None, 
>grumpy=None, happy=None, sleepy=None,
>sneezy=None):
> if bashful is None:
> bashful = self.bashful
> if doc is None:
> doc = self.doc
> if dopey is None:
> dopey = self.dopey
> if grumpy is None:
> grumpy = self.grumpy
> if happy is None:
> happy = self.happy
> if sleepy is None:
> sleepy = self.sleepy
> if sneezy is None:
> sneezy = self.sneezy
> # now do the real work...
> 
> def eggs(self, bashful=None, # etc... 
>):
> if bashful is None:
> bashful = self.bashful
> # and so on
>  
> 
> There's a lot of tedious boilerplate repetition in this, and to add 
> insult to injury the class is still under active development with an 
> unstable API, so every time I change one of the parameters, or add a new 
> one, I have to change it in over a dozen places.
> 
> Is there a good fix for this to reduce the amount of boilerplate?
> 
> 
> Thanks,
> 
> 
> 
> -- 
> Steve

What about something along these lines:

from inspect import getargspec, getargvalues


class Demo(object):

def __init__(self, a=None, b=10, c='oops'):
spec = getargspec(self.__init__)
for key, value in zip(spec.args[1:], spec.defaults):
setattr(self, key, value)

def foo(self, *args, **kwargs):
assert len(args) == 0

for k, v in kwargs.items():
try:
getattr(self, k)
except AttributeError:
print('*** error: attribute {} does not exist.'.format(k))

setattr(self, k, v)


d = Demo()
print(d.a)
d.foo(a=3.14)
print(d.a)

d.foo(q='this will raise')

So, use the inspect module to detect the valid arguments
from the class initializer. Then use **kwargs in every 
class method. It would be nice if the full method signature
can be kept, but I have not yet figured out if this is
possible. 

Marco
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Re: Dynamically replacing an objects __class__; is it safe?

[marco . nawijn]

On Wednesday, March 15, 2017 at 11:33:56 AM UTC+1, Peter Otten wrote:
> marco.naw...@colosso.nl wrote:
> 
> > Dear All,
> > 
> > Summary of the question:
> > Is it generally safe to dynamically change an objects class; if not
> > under which conditions can it be considered safe.
> > 
> > Context:
> > Given the code below, I have no direct control over Base and M1. M1
> > is a instantiated by 'calling' the read-only property of Base.
> > I would like to transparently switch behaviour from M1 to M2. I have
> > tried several things, but finally settled on the code below. Although
> > it works really well, I am not sure whether I am about to shoot myself
> > in the foot. In short, what I do is derive from Base, shadow the read-only
> > property 'my_prop' so it returns M2 and finally replace an objects
> > __class__ attribute with my derived class.
> > 
> > Any thoughts or comments?
> 
> Saying that something is "safe" is always problematic. I'd rather look for 
> ways to break the code and then decide if you can live with these potential 
> problems. I'll start with
> 
> - If Base is reimplemented in C __class__ may become read-only
> - my_prop may be accessed by Base methods and expect an M1 instance

Ok. These are valid points. The first is not a real concern to me at the
moment. The whole purpose of Base is to provide a higher level interface
to the underlying C/C++ code.

The second is more interesting. I was aware of this and checked the source
code of the library. I know an M1 instance is not directly used by Base.
In addition, I expose the exact same interface in M2. 

Thanks for the feedback. Much appreciated!

Marco
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Dynamically replacing an objects __class__; is it safe?

[marco . nawijn]

Dear All,

Summary of the question:
Is it generally safe to dynamically change an objects class; if not 
under which conditions can it be considered safe.

Context:
Given the code below, I have no direct control over Base and M1. M1
is a instantiated by 'calling' the read-only property of Base. 
I would like to transparently switch behaviour from M1 to M2. I have
tried several things, but finally settled on the code below. Although
it works really well, I am not sure whether I am about to shoot myself 
in the foot. In short, what I do is derive from Base, shadow the read-only
property 'my_prop' so it returns M2 and finally replace an objects __class__
attribute with my derived class.

Any thoughts or comments?

(code below is Python 3)

class M1(object):

def __init__(self):
print('Initializing M1')


class M2(object):

 
def __init__(self): 
 
print('Initializing M2')
 

 

 
class Base(object): 
 

 
@property   
 
def my_prop(self):  
 
return M1()


class ShadowBase(Base):

@property
def my_prop(self):
return M2()

if __name__ == '__main__':

o = Base()
o.my_prop
# Prints 'Initializing M1'

o = Base()
o.__class__ = ShadowBase
o.my_prop
# Prints 'Initializing M2'
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Re: best way to read a huge ascii file.

[marco . nawijn]

On Tuesday, November 29, 2016 at 3:18:29 PM UTC+1, Heli wrote:
> Hi all, 
> 
> Let me update my question, I have an ascii file(7G) which has around 100M 
> lines.  I read this file using : 
> 
> f=np.loadtxt(os.path.join(dir,myfile),delimiter=None,skiprows=0) 
> 
> x=f[:,1] 
> y=f[:,2] 
> z=f[:,3] 
> id=f[:,0] 
> 
> I will need the x,y,z and id arrays later for interpolations. The problem is 
> reading the file takes around 80 min while the interpolation only takes 15 
> mins.
> 
> I tried to get the memory increment used by each line of the script using 
> python memory_profiler module.
> 
> The following line which reads the entire 7.4 GB file increments the memory 
> usage by 3206.898 MiB (3.36 GB). First question is Why it does not increment 
> the memory usage by 7.4 GB?
> 
> f=np.loadtxt(os.path.join(dir,myfile),delimiter=None,skiprows=0) 
> 
> The following 4 lines do not increment the memory at all. 
> x=f[:,1] 
> y=f[:,2] 
> z=f[:,3] 
> id=f[:,0] 
> 
> Finally I still would appreciate if you could recommend me what is the most 
> optimized way to read/write to files in python? are numpy np.loadtxt and 
> np.savetxt the best?
> 
> Thanks in Advance,

Hi,

Have you considered storing the data in HDF5? There is an excellent Python
interface for this (see: http://www.h5py.org/). The advantage that you will
have is that no text to number conversion has to applied anymore. You can
directly operate on the datasets in the HDF5 database. 

If you would go this direction, the following would get you started:

>>> import h5py
>>> import numpy
>>> from numpy import uint32, float32, arange

>>> fd = h5py.File('demo.h5', mode='w') # Note that this will truncate
# the file, use 'r' or 'a' if you
# want to open an existing file
>>> observations = fd.create_group('/observations')
>>> N = 100 
>>> observations.create_dataset('id', data=arange(0, N, dtype=uint32))
>>> observations.create_dataset('x', data=numpy.random.random(N), dtype=float32)
>>> observations.create_dataset('y', data=numpy.random.random(N), dtype=float32)
>>> observations.create_dataset('z', data=numpy.random.random(N), dtype=float32)
>>> 
>>> fd.close()

Note that you can also combine x,y and z in a single dataset if you want to.
See the documentation for datasets for more information 
http://docs.h5py.org/en/latest/high/dataset.html

I would also advise you to carefully select the proper dtype for the arrays.
In particular if you know the value range for your datasets. This can save
you a lot of disk space and probably will increase the performance a little.

Marco
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Re: data interpolation

[marco . nawijn]

On Thursday, November 3, 2016 at 11:08:34 AM UTC+1, Heli wrote:
> Hi, 
> 
> I have a question about data interpolation using python. I have a big ascii 
> file containg data in the following format and around 200M points. 
> 
> id, xcoordinate, ycoordinate, zcoordinate
> 
> then I have a second file containing data in the following format, ( 2M 
> values) 
> 
> id, xcoordinate, ycoordinate, zcoordinate, value1, value2, value3,..., valueN
> 
> I would need to get values for x,y,z coordinates of file 1 from values of 
> file2.  
> 
> I don´t know whether my data in file1 and 2 is from structured or 
> unstructured grid source. I was wondering which interpolation module either 
> from scipy or scikit-learn you recommend me to use?
> 
> I would also appreciate if you could recommend me some sample 
> example/reference. 
> 
> Thanks in Advance for your help,

Take a look at the scipy.spatial.KDTree class:
https://docs.scipy.org/doc/scipy-0.14.0/reference/generated/scipy.spatial.KDTree.html

Given your example, you would build the tree (using the coordinates) 
from the second file. Subsequently, you can use one of the query 
methods for every point in your first file. From this it is up to 
you how to transfer (interpolate) the values.

Marco


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Re: get the sum of differences between integers in a list

[marco . nawijn]

On Wednesday, September 21, 2016 at 4:14:10 PM UTC+2, Daiyue Weng wrote:
> Hi, first of all, let me rephase the problem.
> 
> For an arbitrary list of integers (the integers in the list are not
> necessary to be sequential), e.g. [1,2,3,6,8,9,10,11,13],
> 
> if a set of consecutive integers having a difference of 1 between them, put
> them in a list, i.e. there are two such lists in this example,
> 
> [1,2,3],
> 
> [8,9,10,11],
> 
> and then put such lists in another list (i.e. [[1,2,3], [8,9,10,11]]). Put
> the rest integers (non-sequential) in a separated list, i.e.
> 
> `[6, 13]`.
> 
> Note that, the problem only considers sequential integers with step_size =
> 1.
> 
> I tried to use itertools.groupby and itertools.count,
> 
> from itertools import groupby, count
> lst = [1,2,3,6,8,9,10,11,13]
> c = count()
> result = [list(g) for i, g in groupby(lst, key=lambda x: x-next(c))]
> 
> but the result is close to the requirement shown as a list of lists,
> 
> [[1, 2, 3], [6], [8, 9, 10, 11], [13]]
> 
> but it didn't separate sequential lists from non-sequential ones.
> Also, I couldn't find a way to put [6] and [13] in a single list.
> 
> I have also tried to separate sequential lists from non-sequential ones,
> 
> result = [list(g) for i, g in groupby(lst, key=lambda x: x-next(c) == 1)] #
> tried to extract [1,2,3] and [8,9,10,11] from the list
> 
> or
> 
> result = [list(g) for i, g in groupby(lst, key=lambda x: x-next(c) > 1)] #
> tried to extract [6] and [13] from the list
> 
> but they all ended up with
> 
> [[1, 2, 3], [6, 8, 9, 10, 11, 13]]
> 
> So two questions here,
> 
> 1. How does itertools.groupby key function work in my case?
> 
> 2. How to improve the program to achieve my goals?
> 
> 
> Many thanks
> 
> On 21 September 2016 at 00:19, John Pote  wrote:
> 
> > On 20/09/2016 12:52, Daiyue Weng wrote:
> >
> > Hi, I have a list numbers say,
> >>
> >> [1,2,3,4,6,8,9,10,11]
> >>
> >> First, I want to calculate the sum of the differences between the numbers
> >> in the list.
> >>
> > At least for this first part a little pencil, paper and algebra yields a
> > simple formula of constant and minimal calculation time. I had an intuitive
> > guess and wrote down the sum of differences for a couple of examples,
> > [1, 2, 5]   => 4
> > [9, 11, 17, 19] => 10
> > It works for negative differences as well,
> > [1, 2, 5, 1]=> 0
> > The trick is to spot the relation between the sum of differences and the
> > numbers in the list. A few lines of algebra then gave a very simple formula.
> >
> > As for the rest it's down to code as others have hinted at.
> >
> > Second, if a sequence of numbers having a difference of 1, put them in a
> >> list, i.e. there are two such lists,
> >>
> >> [1,2,3]
> >>
> >> [8,9,10,11]
> >>
> >> and also put the rest numbers in another list, i.e. there is only one such
> >> list in the example,
> >>
> >> [6].
> >>
> >> Third, get the lists with the max/min sizes from above, i.e. in this
> >> example, the max list is,
> >>
> >> [8,9,10,11]
> >>
> >> min list is
> >>
> >> [1,2,3].
> >>
> >> What's the best way to implement this?
> >>
> >> cheers
> >>
> >
> > --
> > https://mail.python.org/mailman/listinfo/python-list
> >
On Wednesday, September 21, 2016 at 4:14:10 PM UTC+2, Daiyue Weng wrote:
> Hi, first of all, let me rephase the problem.
> 
> For an arbitrary list of integers (the integers in the list are not
> necessary to be sequential), e.g. [1,2,3,6,8,9,10,11,13],
> 
> if a set of consecutive integers having a difference of 1 between them, put
> them in a list, i.e. there are two such lists in this example,
> 
> [1,2,3],
> 
> [8,9,10,11],
> 
> and then put such lists in another list (i.e. [[1,2,3], [8,9,10,11]]). Put
> the rest integers (non-sequential) in a separated list, i.e.
> 
> `[6, 13]`.
> 
> Note that, the problem only considers sequential integers with step_size =
> 1.
> 
> I tried to use itertools.groupby and itertools.count,
> 
> from itertools import groupby, count
> lst = [1,2,3,6,8,9,10,11,13]
> c = count()
> result = [list(g) for i, g in groupby(lst, key=lambda x: x-next(c))]
> 
> but the result is close to the requirement shown as a list of lists,
> 
> [[1, 2, 3], [6], [8, 9, 10, 11], [13]]
> 
> but it didn't separate sequential lists from non-sequential ones.
> Also, I couldn't find a way to put [6] and [13] in a single list.
> 
> I have also tried to separate sequential lists from non-sequential ones,
> 
> result = [list(g) for i, g in groupby(lst, key=lambda x: x-next(c) == 1)] #
> tried to extract [1,2,3] and [8,9,10,11] from the list
> 
> or
> 
> result = [list(g) for i, g in groupby(lst, key=lambda x: x-next(c) > 1)] #
> tried to extract [6] and [13] from the list
> 
> but they all ended up with
> 
> [[1, 2, 3], [6, 8, 9, 10, 11, 13]]
> 
> So two questions here,
> 
> 1. How does itertools.groupby key function work in my case?
> 
> 2. How to improve the program to achieve my goals?
> 
> 
> Many thanks
> 
> On 21 September 

Re: passing dictionay as argument

[marco . nawijn]

On Monday, June 13, 2016 at 12:54:45 PM UTC+2, Arshpreet Singh wrote:
> I have to pass dictionary as function argument for following code:
> 
> 
> import authorize
> 
> authorize.Configuration.configure(
> authorize.Environment.TEST,
> 'api_login_id',
> 'api_transaction_key',
> )
> 
> result = authorize.Transaction.sale({
> 'amount': 40.00,
> 
> 'credit_card': {
> 'card_number': '4111',
> 'expiration_date': '04/2014',
> 'card_code': '343',
> }
> 
> })
> 
> result.transaction_response.trans_id
> 
> 
> 
> I want to define 'credit-card' dictionary as argument in the function as 
> follows but it returns syntax error:
> 
> 
> 
> # define dictionary outside the function call: 
> credit_card={
> 'card_number': '4111',
> 'expiration_date': '04/2014',
> 'card_code': '343',
> }
> 
> import authorize
> 
> authorize.Configuration.configure(
> authorize.Environment.TEST,
> 'api_login_id',
> 'api_transaction_key',
> )
> 
> result = authorize.Transaction.sale({'amount': 40.00,credit_card})
> 
> result.transaction_response.trans_id
> 
> it returns following error:
> 
> result = authorize.Transaction.sale({40.00,credit_card})
> TypeError: unhashable type: 'dict'
> 
> Do I need to make changes in authorize.Transaction.sale() source code?

You explicitly need to specify the key for credit_card in the
call to sale(..). I have not run the code myself, but I believe it
will work like this:

result = authorize.Transaction.sale({'amount': 40.00,'credit_card': 
credit_card}) 
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Re: More list building

[marco . nawijn]

On Wednesday, May 11, 2016 at 7:22:09 PM UTC+2, DFS wrote:
> Have:
> p1 = ['Now', 'the', 'for', 'good']
> p2 = ['is', 'time', 'all', 'men']
> 
> want
> [('Now','is','the','time'), ('for','all','good','men')]
> 
> This works:
> 
> p = []
> for i in xrange(0,len(p1),2):
>   p.insert(i,(p1[i],p2[i],p1[i+1],p2[i+1]))
> 
> 
> But it seems clunky.
> 
> Better way(s)?
> 
> Thanks

Another way using some array manipulation:
(using Python 2.7 and numpy)

# coding: utf-8
import numpy as np

p1 = np.array(('Now', 'the', 'for', 'good'))
p2 = np.array(('is', 'time', 'all', 'men'))

p1s = np.split(p1, 2)
p2s = np.split(p2, 2)

a1 = np.vstack((p1, p2))

r1 = np.hstack((a1[:, 0], a1[:, 1]))
r2 = np.hstack((a1[:, 2], a1[:, 3]))

print r1
print r2

Produces the following output:
['Now' 'is' 'the' 'time']
['for' 'all' 'good' 'men']
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Re: Phyton

[marco . nawijn]

On Sunday, March 6, 2016 at 6:10:22 PM UTC+1, Mark Lawrence wrote:
> On 06/03/2016 15:28, marco.naw...@colosso.nl wrote:
> > On Sunday, March 6, 2016 at 3:16:19 PM UTC+1, Diego ... wrote:
> >> Hello! I have a question in an exercise that says : Write an expression to 
> >> determine whether a person should or should not pay tax . Consider paying 
> >> tax people whose salary is greater than R $ 1,200.00
> >>
> >> I do not know how to mount the logical expression !!!
> >>
> >> It's like:
> >>
> >> salary = 1250
> >> tax = Not True
> >> salary > 1200 or not tax 
> >
> > Hello Diego,
> >
> > You are looking for the "if" statement. See the link below for
> > the corresponding documentation:
> > https://docs.python.org/2/tutorial/controlflow.html
> >
> > Your example would become something like:
> >
> > salary = 1250.
> > if salary > 1200:
> >  has_to_pay_tax = True
> > else:
> >  has_to_pay_tax = False
> >
> > Marco
> >
> 
> Why in the year 2016 are people still giving links to the Luddite Python 
> 2 docs?
> 
> -- 
> My fellow Pythonistas, ask not what our language can do for you, ask
> what you can do for our language.
> 
> Mark Lawrence



On Sunday, March 6, 2016 at 6:10:22 PM UTC+1, Mark Lawrence wrote:
> On 06/03/2016 15:28, marco.naw...@colosso.nl wrote:
> > On Sunday, March 6, 2016 at 3:16:19 PM UTC+1, Diego ... wrote:
> >> Hello! I have a question in an exercise that says : Write an expression to 
> >> determine whether a person should or should not pay tax . Consider paying 
> >> tax people whose salary is greater than R $ 1,200.00
> >>
> >> I do not know how to mount the logical expression !!!
> >>
> >> It's like:
> >>
> >> salary = 1250
> >> tax = Not True
> >> salary > 1200 or not tax 
> >
> > Hello Diego,
> >
> > You are looking for the "if" statement. See the link below for
> > the corresponding documentation:
> > https://docs.python.org/2/tutorial/controlflow.html
> >
> > Your example would become something like:
> >
> > salary = 1250.
> > if salary > 1200:
> >  has_to_pay_tax = True
> > else:
> >  has_to_pay_tax = False
> >
> > Marco
> >
> 
> Why in the year 2016 are people still giving links to the Luddite Python 
> 2 docs?
> 
> -- 
> My fellow Pythonistas, ask not what our language can do for you, ask
> what you can do for our language.
> 
> Mark Lawrence


> Why in the year 2016 are people still giving links to the Luddite Python 
>2 docs?

As Ian already mentioned, the Python 2 docs came up as the first hit on
Google. However, I agree with you that for a newcomers to Python a link
to Python 3 would probably have been more appropriate (not that I believe
the content of the sections would be any different). 

As a side note, you are probably aware that if you look at the Linux
ecosystems there are still a lot of distributions that have Python 2
as a default. There are still also large mainstream libraries that
do not (or just very recently) have support for Python 3. For me this
in particular applied to VTK. I am now finally ready to move to Python 3.

Marco
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Re: Phyton

[marco . nawijn]

On Sunday, March 6, 2016 at 3:16:19 PM UTC+1, Diego ... wrote:
> Hello! I have a question in an exercise that says : Write an expression to 
> determine whether a person should or should not pay tax . Consider paying tax 
> people whose salary is greater than R $ 1,200.00
> 
> I do not know how to mount the logical expression !!!
> 
> It's like:
> 
> salary = 1250
> tax = Not True
> salary > 1200 or not tax 

Hello Diego,

You are looking for the "if" statement. See the link below for
the corresponding documentation:
   https://docs.python.org/2/tutorial/controlflow.html

Your example would become something like:

salary = 1250.
if salary > 1200:
has_to_pay_tax = True
else:
has_to_pay_tax = False

Marco
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Re: Cycling through iterables diagonally

[marco . nawijn]

On Friday, February 26, 2016 at 8:44:38 AM UTC+1, Pablo Lucena wrote:
> Hello,
> 
> I am trying to accomplish the following:
> 
> Say I have a group of 4 lists as follows:
> 
> l1 = ['a1', 'a2', 'a3', 'a4']
> l2 = ['b1', 'b2', 'b3', 'b4']
> l3 = ['c1', 'c2', 'c3', 'c4']
> l4 = ['d1', 'd2', 'd3', 'd4']
> 
> I would like to cycle through these lists "diagonally" in groups of
> len(list) (in this example, each list has 4 items).
> 
> cycle1: a1, b2, b3, b4
> cycle2: a2, b3, c4, d1
> cycle3: a3, b4, c1, d2
> cycle4: a4, b1, c2, d3
> 
> The way I thought about doing this is as follows:
> 
> from collections import deque
> from itertools import cycle
> 
> l1 = deque(['a1', 'a2', 'a3', 'a4'])
> l2 = deque(['b1', 'b2', 'b3', 'b4'])
> l3 = deque(['c1', 'c2', 'c3', 'c4'])
> l4 = deque(['d1', 'd2', 'd3', 'd4'])
> 
> l1.rotate(-0)
> l2.rotate(-1)
> l3.rotate(-2)
> l4.rotate(-3)
> 
> groups = cycle([l1, l2, l3, l4])
> 
> In [115]: for group in groups:
>.: if not group:
>.: break
>.: print(group.popleft())
>.:
> a1
> b2
> c3
> d4
> a2
> b3
> c4
> d1
> a3
> b4
> c1
> d2
> a4
> b1
> c2
> d3
> 
> Prior to this I was mucking around with index counting while looping, and
> popping lists out of a deque, popping an item out of the list, and
> appending the list back into the deque during each iteration.
> 
> Is there a better/cleaner way to do this? I was hoping for some cool
> itertools logic =)
> 
> Thanks!
> 
> 
> -- 
> *Pablo*

Hello Pablo,

If you don't mind using third-party packages you 
could this quite straighforward with numpy:
(Python 2.7)

import numpy as np

a = np.array([
  ('a1', 'a2', 'a3', 'a4'),
  ('b1', 'b2', 'b3', 'b4'),
  ('c1', 'c2', 'c3', 'c4'),
  ('d1', 'd2', 'd3', 'd4')], dtype=str)

nrows, ncols = a.shape

for i in range(ncols):
print np.diag(np.roll(a, -i, axis=1))

This prints:

['a1' 'b2' 'c3' 'd4']
['a2' 'b3' 'c4' 'd1']
['a3' 'b4' 'c1' 'd2']
['a4' 'b1' 'c2' 'd3']

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Re: [newbie] how to create log files

[marco . nawijn]

Hello Jens,

Are you aware of Python's own logging facility? It is quite powerful
and flexible.

Python 2:
  https://docs.python.org/2/library/logging.html

Python 3:
  https://docs.python.org/3/library/logging.html

Marco
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Re: Using tuple as parameter to a function

[marco . nawijn]

On Monday, November 9, 2015 at 2:58:21 PM UTC+1, Chris Angelico wrote:
> On Tue, Nov 10, 2015 at 12:40 AM, Cecil Westerhof  wrote:
> > I was thinking about something like:
> > values = (( 1, 100), ( 2, 100), ( 5, 100),
> >10, 100), (20, 100), (40, 100))
> > for value in values:
> > do_stress_test('sqlite',   ???)
> > do_stress_test('postgres', ???)
> >
> > Is this possible? If so: what do I put at the place of the '???'?
> >
> > I could change the second and third parameter to a tuple as the second
> > parameter, but I prefer three parameters if that would be possible.
> 
> Easy! Just unpack the tuple. Two options:
> 
> # Unpack in the loop
> for count, size in values:
> do_stress_test('sqlite', count, size)
> do_stress_test('postgres', count, size)
> 
> # Unpack in the function call
> for value in values:
> do_stress_test('sqlite', *value)
> do_stress_test('postgres', *value)
> 
> Either will work. For what you're doing here, I'd be inclined to the
> first option, so you can give the values appropriate names (I'm
> completely guessing here that they might be some sort of iteration
> count and pool size; use names that make sense to your program); the
> other option looks uglier in this particular instance, though it's a
> more direct answer to your question.
> 
> This is one of Python's best-kept secrets, I think. It's not easy to
> stumble on it, but it's so handy once you know about it.
> 
> ChrisA

If the two numbers are actually conceptually connected, you could
consider passing them as a namedtuple. The function would then 
receive two parameters instead of three. Something like the
following (expanding on ChrisA's example):

from collections import namedtuple

StressParameters = namedtuple('StressParameters', ('count', 'size'))

def do_stress_test(db_backend, stress_parameters):
   # Some useful stuff...
   count = stress_parameters.count
   size = stress_parameters.size
   # More useful stuff

parameters = [StressParameters(1, 100), StressParameters(2,100)]

for p in parameters:
do_stress_test('sqlite', p)
do_stress_test('postgres', p)
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Re: Python PNG Viewer(Browser Based)

[marco . nawijn]

On Tuesday, November 3, 2015 at 12:55:09 PM UTC+1, Arshpreet Singh wrote:
> Hello Everyone,
> 
> I am looking for Browser-based PNG file viewer written in
> Python.(Flask framework preferably)
> 
> Following project(Flask-Based) provides many things(File manager as
> well as file viewer)  but it does not support PNG files.
> 
> https://github.com/vmi356/filemanager
> 
> Any idea if I have to write my own browser based PNG viewer from
> scratch(Using PIL or other required library)
> 
> On the other side if I have to write only Desktop-based only two lines
> are enough to do many things:
> 
> Like,
> 
> from PIL import Image
> f = Image.open("file.png").show()
> 
> 
> But I am not getting right sense that how to make possible using Python+Flask.
> 
> Hope I am able to tell my problem?

Well, if you only want to open the PNG file in the webbrowser
(in contrast of serving them over the internet), you can do it
in two lines too:

import webbrowser
webbrowser.open('file.png')

But this is probably not what you want.

M.
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Re: Python, convert an integer into an index?

[marco . nawijn]

On Wednesday, September 23, 2015 at 1:27:51 AM UTC+2, MRAB wrote:
> On 2015-09-22 23:21, Laura Creighton wrote:
> > In a message of Tue, 22 Sep 2015 14:43:55 -0700, Chris Roberts writes:
> >>
> >>
> >>(How do I make it into an index? )
> >>Preferably something fairly easy to understand as I am new at this.
> >>
> >>results = 134523  #(Integer)
> >>
> >>Desired:
> >>results = [1, 2, 3, 4, 5, 2, 3]   #(INDEX)
> >>
> >>Somehow I see ways to convert index to list to int, but not back again.
> >>
> >>Thanks,
> >>crzzy1
> >
> > You need to convert your results into a string first.
> >
> > result_int=1234523
> > result_list=[]
> >
> > for digit in str(result_int):
> >  result_list.append(int(digit))
> >
> > digit will be assigned to successive 1 character long strings.  Since
> > you wanted a list of integers, you have to convert it back.
> >
> > If you are learning python you may be interested in the tutor mailing
> > list. https://mail.python.org/mailman/listinfo/tutor
> >
> A shorter way using strings:
> 
> >>> results = 134523
> >>> list(map(int, str(results)))
> [1, 3, 4, 5, 2, 3]
Or you can use a list comprehension:

>>> result = [int(c) for c in str(134523)]
>>> print result
[1, 3, 4, 5, 2, 3]
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Re: Packaging and deployment of standalone Python applications?

[marco . nawijn]

On Monday, September 14, 2015 at 8:58:51 AM UTC+2, Kristian Rink wrote:
> Folks;
> 
> coming from a server-sided Java background, I'm recently exploring frameworks 
> such as cherrypy or webpy for building RESTful services, which is quite a 
> breeze and a pretty pleasant experience; however one thing so far bugs me: 
> Using Java tooling and libraries such as DropWizard, it is pretty 
> straightforward to build an "all-inclusive" application containing (a) all 
> code of my own, (b) all required dependencies, (c) all other resources and, 
> if required, even (d) a Java virtual machine in one large .zip file which can 
> easily be copied to a clean Linux VM, unzipped and started there.
> 
> Are there ways of doing so using Python, too? I'd like to set up a project 
> structure / working environment that includes all Python 3rd party libraries, 
> my own code and maybe even a "standard" Python runtime for 64bit Linux 
> systems (to not depend too much on what version a certain Linux distribution 
> actually ships) and focus on doing deployment to various machines at best by 
> simply copying these packages around. 
> 
> Any pointers, ideas, inspirations on that greatly appreciated - even in total 
> different ways if what I am about to do is completely off anyone would do it 
> in a Python environment. ;)
> 
> TIA and all the best,
> Kristian

If your business-cases allows it, I would seriously consider using
Docker. I makes it pretty straightforward to move your deployments
around from your development machine, to a test setup, to a cloud
provider (e.g. AWS) etc.

Lack or incomplete support on Windows systems is a little bit a 
deal breaker, but this situation is improving quickly.

Marco
 
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Re: From logging to files to a better solution: syslog, Sentry, Logstash, ....

[marco . nawijn]

On Friday, September 11, 2015 at 9:22:42 AM UTC+2, Thomas Güttler wrote:
> Am Donnerstag, 10. September 2015 08:42:47 UTC+2 schrieb dieter:
> > Thomas Güttler writes:
> > > ...
> > > Why we are unhappy with logging to files:
> > >
> > >  - filtering: We don't want to get INFO messages over the VPN.
> > 
> > You can quite easily control at what level messages are logged with
> > the standard Python logging framework. Each handler has a level
> > and will ignore messages at a lower level.
> 
> 
> I want INFO to be logged and stored on the remote host.
> Therefore I must not filter INFO messages.
> 
> I don't want to pull INFO messages over the VPN.
> 
> Ergo, the filtering at Python level does not help in my use case.
> Or I am missing something.
> 
> And now I have an ugly soup. 
> 
> The ugly soup is a text file with not well defined syntax. It looks line
> based. But sometimes there are log messages which span multiple lines 
> 
> Remember: "Life is too short to (re)write parsers"
> 
> Yes, there are tools to parse that soup. But why create this soup in 
> the first place?
> 
> That's why I want to move from file based logging to a different solution.
> 
> Unfortunately there too many choices (graylog, logstash, sentry, ...) :-(
> 
> 
> 
> > >  - Rotating: Rotating files is possible, but somehow cumbersome.
> > 
> > There are standard tools to rotate logfiles.
> > 
> > >  - Support structured logging of values (json) in the future.
> > 
> > Again, the Python logging framework is quite flexible with
> > respect to the format of logged messages.
> > 
> > > ...
> > > Which solution could fit for our environment?
> > 
> > I work for a customer with a similar environment (he uses "Zope" instead
> > of "Django") - and he uses logfiles. The logfiles are automatically
> > rotated and there are in the order of half a dozen to a dozen logfiles
> > per day.
> > 
> > When I have to analyse a problem with the help of the logfiles,
> > I do not copy them via VPN but do the filtering remotely and only
> > copy the filtered portion, if necessary.
> 
> Good to know that I am not the only one running servers in remote intranets.
> 
> Regards,
>   Thomas Güttler

So, if logging to json is on the horizon anyway, why don't you create
something like a MongoDb handler in the standard Python logging framework 
and run a MongoDb server in the client intranet? You could then connect
over VPN to MongoDb, filter the warning/error messages there on the server
side and fetch them to your local systems for analysis.

Marco
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Re: Most Pythonic way to store (small) configuration

[marco . nawijn]

On Sunday, August 2, 2015 at 12:14:51 PM UTC+2, Cecil Westerhof wrote:
 There are a lot of ways to store configuration information:
 - conf file
 - xml file
 - database
 - json file
 - and possible a lot of other ways
 
 I want to write a Python program to display cleaned log files. I do
 not think I need a lot of configuration to be stored:
 - some things relating to the GUI
 - default behaviour
 - default directory
 - log files to display, including some info
   - At least until where it was displayed
 
 Because of this I think a human readable file would be best.
 Personally I do not find XML very readable. So a conf or json file
 looks the most promising to me. And I would have a slight preference
 for a json file.
 
 Any comments, thoughts or tips?
 
 -- 
 Cecil Westerhof
 Senior Software Engineer
 LinkedIn: http://www.linkedin.com/in/cecilwesterhof

Why not use Python files itself as configuration files?
I have done so several times and I am very pleased with
it. I have tried both INI and JSON, but in the end always
settled on using Python itself. If I have to share the
configuration information with other languages (like C++
or Javascript) I use JSON as the 

For those who are interested, I provide a short summary
below on how I handle configuration files.

The scenario I want to support is that there is a hierarchical
set of configuration files (as typically found in Unix like
systems) that can be stored in a system wide folder (like 
/etc/app), in a user folder (like /home/user/.config/app) and
in a local folder.

Each configuration file has a fixed name, not necessarily ending
in .py. So for example, the name of the configuration file
is config.myapp.

Next I start looking for the existence of these files and once
I find them I start merging all the configuration settings into
one Python dictionary. The function that I use can be found below.  
(you need proper import statements, but this is standard Python).

def load_config(config_file, checked=False):
'''Small utility function to load external configuration files.

'''
if checked is False:
if not isfile(config_file) or islink(config_file):
msg = 'Config file %s does not exist.'
LOGGER.warning(msg)
return {}

# Load the module object; we use the imp.load_source function because
# the module configuration typically has a non-standard file extension
# (by default the file is called config.myapp)

module_name = 'm%s' % str(uuid.uuid1()).replace('-', '')

# Prevent bytecode generation for configuration files
sys.dont_write_bytecode = True

config_module = imp.load_source(module_name, config_file)

# Continue with bytecode generation for other normal modules
sys.dont_write_bytecode = False

if not hasattr(config_module, '__config__'):
msg = 'Missing __config__ attribute in configuration file.'
LOGGER.warning(msg)
return {}

else:
return config_module.__config__

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Re: How to import a function from another module...

[marco . nawijn]

On Tuesday, August 4, 2015 at 3:11:41 PM UTC+2, Dwight GoldWinde wrote:
 Thank you, Steven.
 I am a newbie with Python? so I really want to learn how to do it the easy
 way.
 Yes, could you tell me how to put the py.file that contains the function
 in the Python search path???
 
 
 
 BIG SMILE...
 
 Always, Dwight
 
 
 www.3forliving.key.to (video playlist on YouTube)
 www.couragebooks.key.to (all my books on Amazon)
 
 
 
 
 
 
 
 
 On 8/4/15, 9:24 AM, Steven D'Aprano st...@pearwood.info wrote:
 
 On Tue, 4 Aug 2015 09:57 am, Dwight GoldWinde wrote:
 
  I am trying to import a function defined in another module.
 
 You can't use spaces in the name of importable Python modules: change the
 name from Simulate typing.py to simulate_python.py. You can use spaces
 in file names if they are only used as a runnable script and not imported.
 
 Then use this:
 
 from simulate_python import humprint
 
 There's no need to use importlib.
 
 You may need to arrange for the simulate_python file to be placed
 somewhere
 in the Python search path. Do you need help with that?
 
 What you are trying to do with importlib is fight the language. Your life
 will be much simpler if you work within the parameters of how the language
 is designed to work.
 
 
 
 -- 
 Steven
 
 -- 
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Hi Dwight,

There are at least two ways to manipulate your search path, one from
within Python, one by setting/updating an environmental variable
in your operating system.

1. Dynamically add a search path in Python
First note that if you want to know which parts are currently
in the Python search path you can do the following (note that 
means type it in the Python shell and I am using Python 2 syntax)

 import sys
 for path in sys.path:
... print path

So, if you want to add a folder to your search path, in your
script add the following *before* you access attributes etc.
from the module your are trying to use:

sys.path.append(the_path_that_contains_the_py_file)
# Import stuff from the py file here

The downside of this approach is that you have to do this
in every script that accesses information from your .py
file. If you want to do this once and for all, use the
second method

2. Setting/updating the environment variable
You can use the environment variable PYTHONPATH to inform
Python on which search paths it should use (besides the
default ones). 

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Re: Most Pythonic way to store (small) configuration

[marco . nawijn]

On Tuesday, August 4, 2015 at 7:06:33 PM UTC+2, Irmen de Jong wrote:
 On 4-8-2015 16:53, marco.naw...@colosso.nl wrote:
  Why not use Python files itself as configuration files?
 
 It could create a security risk if the config files are user-editable.
 (it will make it easy to inject code into your application)
 
 Irmen

Yes, I am aware of the security risk, but right now I am not too
worried about it. To be honest, JSON would be my preferred 
configuration file format, but as others already mentioned, there is
no standard way of adding comments to a JSON file. 

Marco
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Re: Creating a reliable sandboxed Python environment

[marco . nawijn]

On Tuesday, May 26, 2015 at 4:24:32 AM UTC+2, davi...@gmail.com wrote:
 I am writing a web service that accepts Python programs as input, runs the 
 provided program with some profiling hooks, and returns various information 
 about the program's runtime behavior. To do this in a safe manner, I need to 
 be able to create a sandbox that restricts what the submitted Python program 
 can do on the web server.
 
 Almost all discussion about Python sandboxes I have seen on the internet 
 involves selectively blacklisting functionality that gives access to system 
 resources, such as trying to hide the open builtin to restrict access to 
 file I/O. All such approaches are doomed to fail because you can always find 
 a way around a blacklist.
 
 For my particular sandbox, I wish to allow *only* the following kinds of 
 actions (in a whitelist):
 * reading from stdin  writing to stdout;
 * reading from files, within a set of whitelisted directories;
 * pure Python computation.
 
 In particular all other operations available through system calls are banned. 
 This includes, but is not limited to:
 * writing to files;
 * manipulating network sockets;
 * communicating with other processes.
 
 I believe it is not possible to limit such operations at the Python level. 
 The best you could do is try replacing all the standard library modules, but 
 that is again just a blacklist - it won't prevent a determined attacker from 
 doing things like constructing their own 'code' object and executing it.
 
 It might be necessary to isolate the Python process at the operating system 
 level.
 * A chroot jail on Linux  OS X can limit access to the filesystem. Again 
 this is just a blacklist.
 * No obvious way to block socket creation. Again this would be just a 
 blacklist.
 * No obvious way to detect unapproved system calls and block them.
 
 In the limit, I could dynamically spin up a virtual machine and execute the 
 Python program in the machine. However that's extremely expensive in 
 computational time.
 
 Has anyone on this list attempted to sandbox Python programs in a serious 
 fashion? I'd be interested to hear your approach.
 
 - David

What about launching the Python process in a Docker container?
Spinning up a new container is pretty quick and it might provide
you with enough isolation. Probably not a perfect solution, but
I do believe that it would be easier than trying to sandbox Python
itself.

Marco
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Re: Could not find any downloads that satisfy the requirement novaclient

[marco . nawijn]

On Tuesday, April 7, 2015 at 9:55:58 PM UTC+2, kurt_...@symantec40.com wrote:
 Hi-
 
 While trying to install an OpenStack client on Mac OSX, I get the following:
 
 SymMacToolkit-C02N4H9DG3QD:/ kurt_heiss$ sudo pip install novaclient
 Password:
 The directory '/Users/kurt_heiss/Library/Logs/pip' or its parent directory is 
 not owned by the current user and the debug log has been disabled. Please 
 check the permissions and owner of that directory. If executing pip with 
 sudo, you may want the -H flag.
 The directory '/Users/kurt_heiss/Library/Caches/pip/http' or its parent 
 directory is not owned by the current user and the cache has been disabled. 
 Please check the permissions and owner of that directory. If executing pip 
 with sudo, you may want the -H flag.
 The directory '/Users/kurt_heiss/Library/Caches/pip/http' or its parent 
 directory is not owned by the current user and the cache has been disabled. 
 Please check the permissions and owner of that directory. If executing pip 
 with sudo, you may want the -H flag.
 Collecting novaclient
   Could not find any downloads that satisfy the requirement novaclient
   No distributions at all found for novaclient
 SymMacToolkit-C02N4H9DG3QD:/ kurt_heiss$ 
 
 I changed the permissions on the identified folders as well as tried the -H 
 option to no positive result.
 
 Anybody encounter this issue or suggest a possible workaround?

Hi,

The module you are looking for is named python-novaclient and not novaclient.
You can check for yourself by running pip search novaclient.
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Re: A question about how plot from matplotlib works

[marco . nawijn]

On Thursday, February 19, 2015 at 11:47:53 AM UTC+1, ast wrote:
 Hello
 
  import numpy as np
  import matplotlib.pyplot as plt
  x = np.arange(10)
  y = x**2
  x
 array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
  y
 array([ 0,  1,  4,  9, 16, 25, 36, 49, 64, 81])
  plt.plot(x,y)
 [matplotlib.lines.Line2D object at 0x044F5930]
  plt.show()
 
 
 The question is:
 
 plt.plot() creates an object matplotlib.lines.Line2D but this object is
 not referenced. So this object should disapear from memory. But
 this doesn't happens since plt.show() draws the curve on a graphic
 window. So how does it work ?

Hi,

I have not checked the source code, but pyplot probably implicitly
generates a few objects for you. In particular it probably creates
a default figure, so when you say plt.plot(x,y), behind the scenes
pyplot will request the current figure and add the Line2D items to it.

Marco
 
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Re: operator module functions

[marco . nawijn]

For me it makes sense. operator.add should be used in a global context
(I don't know how to express it otherwise). So you provide it with the 
two values that you want to add. The .__add__ variants are bound to a
particular instance and you provide it with a single value that you want
to add. 

You also need the dunder versions when you want to implement addition for
user defined types. So although they are similar, I do believe they have
slightly different uses. As an example, you cannot use the dunder versions
for literals.

 2.__add__(3) # Oops, does not work
 a = 2
 a.__add__(3)
5
 import operator
 operator.add(2,3) # Fine

I also think operator.add versus .__add__ is equivalent to the global
getattr() and .__getattr__.

Marco




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Re: Recommended hosting

[marco . nawijn]

On Thursday, October 2, 2014 3:30:38 PM UTC+2, writeson wrote:
 Hi all,
 
 
 
 I'd like to build a web site for myself, essentially a vanity web site to 
 show off whatever web development skills I have, and perhaps do some 
 blogging. I'm a Python developer, so I'd like to develop the site with the 
 following stack:
 
 
 
 web applications written with Python and Flask, running as uwsgi 
 applications. These would support dynamic HTML where needed, but mostly it 
 would provide REST API's.
 
 
 
 static content delivered by Nginx
 
 
 
 Can anyone give me some recommendations for a good hosting company that would 
 allow me work with the above tool set? I'm US based if that makes a 
 difference.
 
 
 
 Thanks in advance!
 
 Doug

Doug,

Also don't forget the new kid on the block Docker! So, you can build your 
webapp locally on your machine, deploy it (also locally) in a Docker 
container. Test it and then deploy it in the cloud. You have lots of 
options for this.

I am the process of doing this myself and I like it a lot! 

Marco



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Re: dict to boolean expression, how to?

[marco . nawijn]

Hi,

Are you aware of the Python operator module?
It provides function equivalents of all (most?)
python operator. So instead of a==b, you can
state operator.eq(a,b). As a result, you can
loop over the key/value pairs in the dict and
built your logic with the operator.eq, 
operator.and_, and operator.or_ (notice the 
trailing underscore to avoid clashing with
normal and and or statements.

Marco
 
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Re: Standard library Help

[marco . nawijn]

On Friday, July 11, 2014 10:32:32 AM UTC+2, Nicholas Cannon wrote:
 Hey i would like to know alot more about the standard library and all of its 
 functions and so on and i know it is huge and i would basically like to learn 
 only the useful stuff that i could use and all of those features. i have been 
 looking around and i cant really find anything so i wondering if you guys 
 would know any places to learn it.

Hi Nicholas,

Have you tried the library reference [1]? If so, can you
explain why it is not sufficient for your needs?


[1] https://docs.python.org/3/library/index.html
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Re: how can i get body values?

[marco . nawijn]

On Friday, July 11, 2014 11:37:17 AM UTC+2, Frank Liou wrote:
 how can i get body values use variable to Separate catch?
 
 
 
 https://lh3.googleusercontent.com/-6Ywp4GukuCM/U7-vhF0nzuI/Bv4/Ovcr1O2FScs/s1600/321.jpg
 
 
 
 i want to catch name and key values
 
 
 
 now i use request.data
 
 
 
 i can catch all the body 
 
 
 
 but how can i use variable to separate and catch?

Hi Frank,

In general, you will get better response from the
group if you post the code that you have so far and
ask questions on why it doesn't work or how to proceed.

In case of your particular problem, the answer is 
it depends. Do you use the Python standard library, 
or a webserver framework like tornado or cherrypy? 

If you still have a choice, I would recommend to use
a framework like cherrypy. It makes your life a lot 
easier.

Regards,

Marco
 
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Re: Python While loop Takes too much time.

[marco . nawijn]

On Monday, June 30, 2014 1:32:23 PM UTC+2, Jaydeep Patil wrote:
 I have did excel automation using python.
 
 In my code I am creating python dictionaries for different three columns data 
 at a time.There are are many rows above 4000. Lets have look in below 
 function. Why it is taking too much time?
 
 
 
 Code:
 
 
 
 def transientTestDict(self,ws,startrow,startcol):
 
 
 
 self.hwaDict = OrderedDict()
 
 self.yawRateDict = OrderedDict()
 
 
 
 rng = ws.Cells(startrow,startcol)
 
 
 
 while not rng.Value is None:
 
 r = rng.Row
 
 c = rng.Column
 
 
 
 time = rng.Value
 
 
 
 rng1 = rng.GetOffset(0,1)
 
 hwa = rng1.Value
 
 
 
 rng2 = rng.GetOffset(0,2)
 
 yawrate = rng2.Value
 
 
 
 self.hwaDict[time] = hwa,rng.Row,rng.Column
 
 self.yawRateDict[time] = yawrate,rng.Row,rng.Column
 
 
 
 rng = ws.Cells(r+1,c)
 
 
 
 
 
 
 
 Please have look in above code  suggest me to improve speed of my code.
 
 
 
 
 
 
 
 Regards
 
 Jaydeep Patil

Hi Jaydeep,

I agree with Peter. I would avoid moving from cell to
cell through the EXCEL interface if you can avoid.

If possible, I would try to read ranges from EXCEL into
a python list (or maybe numpy arrays) and do the processing
in Python. In the past I even dumped an EXCEL sheet as a
CSV file and then used the numpy recfromcsv function to 
process the data.

If you are really brave, dump EXCEL alltogether :) and do
all the work in Python (have you already tried IPython 
notebook?).

Regards,

Marco

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Re: Why isn't this code working how I want it to?

[Marco Nawijn]

On Saturday, October 12, 2013 10:56:27 AM UTC+2, reuben...@gmail.com wrote:
 I've been working on a program and have had to halt it due a slight problem. 
 Here's a basic version of the code:
 
 
 
 a = 'filled'
 
 b = 'filled'
 
 c = 'empty'
 
 d = 'empty'
 
 e = 'filled'
 
 f = 'empty'
 
 g = 'filled'
 
 
 
 testdict = {a : 'apple' , b : 'banana' , c : 'cake' , d : 'damson' , e : 
 'eggs' , f : 'fish' , g : 'glue'}
 
 
 
 
 
 Now what I want to do, is if a variable is filled, print it out. This however 
 isn't working how I planned. The following doesn't work.
 
 
 
 for fillempt in testdict:
 
 if fillempt == 'filled':
 
 print(testdict[fillempt])
 
 
 
 All this does though, is print glue, where I'd want it to print:
 
 
 
 apple
 
 banana
 
 eggs
 
 glue
 
 
 
 Perhaps a dictionary isn't the best way to do this.. I wonder what else I can 
 do...
 
 
 
 Thanks for any help.

Hi,

Remember that keys in a dictionary are unique. So if you defined ( means it 
I typed it at the interactive terminal prompt,

 d = { 'filled' : 'apple' , 'filled' : 'orange' }

and do a 

 print d

it will show:
 
{'filled': 'orange'}

One way to solve this problem is to define two dictionaries. 
One holding the status of the variable, the other one holding
the data. For example:

status = { 'a' : 'filled',  'b' : 'empty', 'c' : 'filled' }
data   = { 'a' : 'orange',  'b' : 'apple', 'c' : 'banana' }

for k in status:
if status[k]=='filled':
print data[k]

Regards and let us know if it works for you,

Marco
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Re: Printing a text over an image

[Marco Nawijn]

On Wednesday, November 7, 2012 5:52:36 PM UTC+1, Martha Morrigan wrote:
 Hi guys,
 
 
 
 Using python, wxpython and sqlite in a windows system, Im trying to
 
 print some certificates/diplomas/cards with a image at background with
 
 the name of person/text over it.
 
 
 
 I know the basic steps to print the text using win32print from Pywin32
 
 but...:
 
 
 
 1) I dont know how to add an image and set it to background.
 
 
 
while .
 
 
 
 .
 
 
 
 # Query sqlite rows and collumn name and set the self.text for
 
 each certificate
 
 
 
 .
 
 
 
 # Now send to printer
 
 
 
 DC = win32ui.CreateDC()
 
 DC.CreatePrinterDC(win32print.GetDefaultPrinter())
 
 
 
 DC.SetMapMode(win32con.MM_TWIPS)
 
 
 
 DC.StartDoc(Certificates Job)
 
 
 
 DC.StartPage()
 
 
 
 ux = 1000
 
 uy = -1000
 
 lx = 5500
 
 ly = -55000
 
 
 
 DC.DrawText(self.text, (ux, uy, lx, ly),win32con.DT_LEFT)
 
 
 
 DC.EndPage()
 
 DC.EndDoc()
 
 
 
 This printer-code is inside a while loop calling each people name from
 
 a sqlite database per check condition.
 
 
 
 
 
 2) All the names of database was printed at same page... how i command
 
 the printer to spit out 1 page per name from the database?
 
 
 
 
 
 3) Any more simple approach or module to deals with printers (paper
 
 and/or pdf) will be welcome.
 
 
 
 Thanks in advance,
 
 
 
 Martha

Hi Martha,

Since you are on windows, why don't you use MS/Word directly from Python. It 
has all the abstractions you need (documents, pages, tables, figures, printing 
etc.). Working with MS/Word through the win32 bindings is really simple.
I have done this a while ago for some automatic report generation. The basic 
routine is to start recording your actions with the MS/Word macro recorder, do 
the things you want to do, stop recording, look at the VB code and guess the 
equivalent Python code. This is not as bad as it sounds. It normally is really 
straightforward.

I am on Linux at the moment, so I cannot present any code examples. Feel free 
to try and post some example code if you get stuck.

Marco
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Re: What's the tidy/elegant way to protect this against null/empty parameters?

[Marco Nawijn]

On Monday, October 15, 2012 1:33:02 PM UTC+2, (unknown) wrote:
 I want to fix an error in some code I have installed, however I don't
 
 really want to just bodge it.
 
 
 
 The function producing the error is:-
 
 
 
 def get_text(self, idx):   # override !
 
 node = self.items[idx]
 
 
 
 a= [
 
 , .join(node.tags),
 
 node.comment,
 
 node.folderName,
 
 cd2rd(node.date),
 
 node.name,
 
 '[' + self.rating_stars[node.rating] + ']'
 
 ] [self.select]
 
 
 
 return a
 
 
 
 
 
 The error occurs when node[] (or at least its members) turn out to be
 
 empty, you get a Traceback that ends with:-
 
 
 
   File /usr/lib/jbrout/jbrout/listview.py, line 608, in draw_cell 
 layout.set_text(self.get_text(thumbnail_num))
 
   File /usr/lib/jbrout/jbrout.py, line 325, in get_text , 
 .join(node.tags),
 
   TypeError: sequence item 0: expected string, NoneType found
 
 
 
 Now its *probably* something higher up the tree causing the problem
 
 (it's only one particular image in 20 thousand or so that breaks
 
 things) but I really want to just get things working.  So, what's the
 
 neatest way to protect the get_text() method from empty data?
 
 
 
 
 
 -- 
 
 Chris Green
Hi,

Instead of protecting against empty data, you could just catch the exception, 
issue a warning and return a default error node which is valid. So something 
like (not tested):

def get_text(self, idx):   # override ! 
node = self.items[idx] 

error_a = A valid, but erroneous representation of a

try:
a= [ 
, .join(node.tags), 
node.comment, 
node.folderName, 
cd2rd(node.date), 
node.name, 
'[' + self.rating_stars[node.rating] + ']' 
] [self.select] 
except TypeError:
  print 'Oops, something went wrong'
  a = error_a
# You should always have a valid a here (or another exception has  
occured)
return a 
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Re: Accessing variables in __init__.py

[Marco Nawijn]

On Tuesday, October 16, 2012 10:48:17 AM UTC+2, Gaudha wrote:
 my_package/
 
   __init__.py
 
   my_module1.py
 
   my_module2.py
 
   variables.py
 
 
 
 I want to define common variables in __init__.py and use the namespace in 
 my_module1.py or my_module2.py. Defining it is not a problem. How can call it 
 from my modules?
 
 
 
 If I define them in a module (say, variables.py), I can call them by 
 importing variables.py in other modules. How can it be done if I define it in 
 __init__.py?
 
 
 
 It may be a silly query as I am newbie in Python. But, I would be grateful to 
 get help.

Hi,

If you store the variables in __init__.py, you can import them from the 
package. So in your case suppose __init__.py contains:
a = 10
b = {1 :Hello, 2: World }

Than if you import my_package, you can access the variables as follows 
(interactive IPython session):

In [1]: import my_package

In [2]: my_pack
my_package   my_package/  

In [2]: my_package.
my_package.a  my_package.b  

In [2]: my_package.a
Out[2]: 10

In [3]: my_package.b
Out[3]: {1: 'Hello', 2: 'World'}

In [4]: 

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Re: Providing a Python wrapper to a C++ type.

[Marco Nawijn]

On Tuesday, October 16, 2012 10:11:52 AM UTC+2, aaron.l...@gmail.com wrote:
 Hi,
 
 
 
 I have a C++ module where I have a defined, working type. How would I make a 
 wrapper for this type to be able to be used in Python? I am familiar(-ish) 
 with the C-API for functions but I can't see concretely how one would include 
 an interface to a type.
 
 
 
 Is it this? http://docs.python.org/release/2.7.3/extending/newtypes.html
 
 
 
 Regards,
 
 Aaron

Hi Aaron,

There are a few ways of doing this. At least three come to my mind:
1. Wrap the C++ type yourself by using handcrafted code implemented with the 
Python C API
2. Use SWIG to wrap the C++ code and (semi) automatically create the wrapper 
(http://www.swig.org/)
3. Use BOOST Python to wrap the C++ code 
(http://www.boost.org/doc/libs/1_51_0/libs/python/doc/index.html)

I would highly discourage (1) unless you are very brave and curious. Ofcourse 
it is a nice excercise, but if you want something to work quickly I would 
recommend to use either (2) or (3).

I have used both SWIG and BOOST Python and either of them worked pretty well 
for me. In the end I selected BOOST Python, because I was only interested in 
the Python wrapping (SWIG could generate many other wrappers as well).

Regards,

Marco
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Re: Is there a way to create kernel log messages via Python?

[Marco Nawijn]

On Tuesday, October 16, 2012 5:43:28 AM UTC+2, J wrote:
 Hi...
 
 
 
 I have a bit of code that does the following:
 
 
 
 uses the syslog module to inject a LOG_INFO message into the syslog on
 
 my linux machine
 
 runs a suspend/resume cycle
 
 uses the syslog module to inkect a LOG_INFO message marking the end of test.
 
 
 
 Then I parse everything between the start and stop markers for certain
 
 items that the Linux kernel logs during a suspend and resume cycle.
 
 
 
 But my  resume complete timing is not as accurate as it could be.
 
 The problem with doing it this way is that while I can find definite
 
 kernel messages that mark various points in the suspend/resume cycle,
 
 the final message when the kernel is done resuming is NOT the point I
 
 actually want to mark.
 
 
 
 Instead, the end point I want is the time of the ending marker itself,
 
 as this happens after certain other things are done such as resumption
 
 of networking services.
 
 
 
 Here's the problem.  I can't just use syslog timestamps.  The reason
 
 is that the syslog timestamps are only indicative of when messages are
 
 written to syslog via syslogd.  The kernel timestamps are different.
 
 For example, the following bits of log are taken from the time the
 
 test starts until the end of the going to sleep kernel messages.
 
 First, note that there's a 5 second difference between the START
 
 marker and the first kernel message.  Next, look at the kernel
 
 timestamps.  The total real time to suspend starts at 421320.380947
 
 and ends at 421322.386355, around 2 seconds later, where the log
 
 messages themselves all state that the events occurred at the same
 
 time.
 
 
 
 Oct 15 10:24:19 klaatu sleep_test: ---SLEEP TEST START 1350296656---
 
 Oct 15 10:25:24 klaatu kernel: [421320.380947] PM: Syncing filesystems ... 
 done.
 
 Oct 15 10:25:24 klaatu kernel: [421320.391282] PM: Preparing system
 
 for mem sleep
 
 [SNIP]
 
 Oct 15 10:25:24 klaatu kernel: [421322.282943] Broke affinity for irq 23
 
 Oct 15 10:25:24 klaatu kernel: [421322.386355] CPU 7 is now offline
 
 
 
 So, what I REALLY want is to inject my start/stop markers into klogd
 
 rather than syslogd.  This will, I hope, give my markers kernel
 
 timestamps rather than syslog timestamps which are not as accurate.
 
 
 
 So does anyone know of a way to do this?  Unfortunately, I've tried
 
 some searching but google doesn't like the term klog, and most of the
 
 hits involved injecting code or other things that are not related at
 
 all.
 
 
 
 Or, if there's a better way to get accurate timestamps, what would that be?

Hi,

I cannot be of too much help here, but is there a userspace/kernel C-interface 
that could be used. If so, you might be able to use the Python ctypes module to 
create messages at the correct moments

Regards,
Marco
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Re: Which book is the best?

[Marco Nawijn]

On Tuesday, October 16, 2012 6:41:29 AM UTC+2, David Hutto wrote:
 On Tue, Oct 16, 2012 at 12:27 AM, 老爷 yujian4newsgr...@gmail.com wrote:
 
  I have strong c++ development experience.  But now I want to study the
 
  python to do some windows setting task, such as editing file, changing the
 
  system setting, doing some network processing.  Please help me which book is
 
  the best?
 
 
 
 
 
 Definitely command line apps/command line usage.
 
 
 
  I could recommend google searches, but use the calls to the OS, and
 
 you can accomplish a good bit of things.
 
 
 
 
 
 -- 
 
 Best Regards,
 
 David Hutto
 
 CEO: http://www.hitwebdevelopment.com

Hi,

Although I agree with the fact the working in the interactive interpreter (may 
I recommend IPython for this) is definitely an efficient way of exploring the 
Python world, I also liked alot the Python Essential Reference (4th edition). 
Since you already understand how to program, the Python essential reference 
quickly guides you through Python language and the standard library.

Regards,

Marco
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Re: numpy - 2D matrix/array - initialization like in Matlab...

[Marco Nawijn]

On Tuesday, October 16, 2012 12:43:09 AM UTC+2, someone wrote:
 On 10/15/2012 11:26 PM, MRAB wrote:
 
  On 2012-10-15 22:09, someone wrote:
 
 
 
  See this:
 
 
 
  ==
 
  In [5]: Dx = numpy.matrix('1 0 0; 0 0.5 -0.5; 0 -0.5 1.5')
 
 
 
  In [6]: Dx
 
  Out[6]:
 
  matrix([[ 1. ,  0. ,  0. ],
 
[ 0. ,  0.5, -0.5],
 
[ 0. , -0.5,  1.5]])
 
  ==
 
 
 
 
 
 
 
  Ok... So now test = 33 and instead of the value 1.5 I want to use the
 
  value of test and put it directly into the matrix (or array):
 
 
 
  ==
 
  In [7]: test=33
 
 
 
  In [8]: Dx = numpy.matrix('1 0 0; 0 0.5 -0.5; 0 -0.5 test')
 
  ---
 
 
 
  NameError Traceback (most recent call
 
  last)
 
  /home/user/something/ipython-input-8-5a43575649e1 in module()
 
   1 Dx = numpy.matrix('1 0 0; 0 0.5 -0.5; 0 -0.5 test')
 
 
 
  /usr/lib/python2.7/dist-packages/numpy/matrixlib/defmatrix.pyc in
 
  __new__(subtype, data, dtype, copy)
 
252
 
253 if isinstance(data, str):
 
  -- 254 data = _convert_from_string(data)
 
255
 
256 # now convert data to an array
 
  .. etc...
 
  ==
 
 
 
 
 
 
 
  So obviously it doesn't understand that I want this:
 
 
 
  ==
 
  In [21]: Dx[2,2]=test
 
 
 
  In [22]: Dx
 
  Out[22]:
 
  matrix([[  1. ,   0. ,   0. ],
 
[  0. ,  33. ,  -0.5],
 
[  0. ,  -0.5,  33. ]])
 
  ==
 
 
 
  Without having to manually change all the individual places using my
 
  variables (test is actually many variables, not just one but I think you
 
  should understand the problem now).
 
 
 
 
 
  How to initialize my array directly using variables ?
 
 
 
  It could also be that I wanted:
 
 
 
  test11 = 1
 
  test12 = 1.5
 
  test13 = 2
 
  test21 = 0
 
  test22 = 5
 
 
 
  Dx = numpy.matrix('test11 test12 test13; test21 test22 -0.5; 0 -0.5 1.5')
 
 
 
  Etc... for many variables...
 
 
 
  Appreciate ANY help, thank you very much!
 
 
 
  What it prints should give you a hint:
 
 
 
Dx = numpy.matrix([[test11, test12, test13], [test21, test22,
 
  -0.5], [0, -0.5, 1.5]])
 
Dx
 
  matrix([[ 1. ,  1.5,  2. ],
 
   [ 0. ,  5. , -0.5],
 
   [ 0. , -0.5,  1.5]])
 
 
 
 Uh, great - thank you very much!
 
 
 
 As you maybe see, I'm only a python newbie so I'm not so good at 
 
 understanding the error messages and reading the source code yet.
 
 
 
 Thank you very much for the solution to the problem! It's highly 
 
 appreciated. Thanks.

Hi,

Also note that you don't need to initialize the array with a string. You could 
directly do it like this:

 a = numpy.array(((1,2,3), (2,3,4), (4,5,6)))

Other things that might be interesting for you are:

# List comprehension (standard python) to convert strings to floats
 vals = [ float(s) for s in 1.0 2.3 1.2.split() ]
produces [1.0, 2.3, 1.2]
 vals = [ float(s) for s in (1.0, 2.3, 1.2) ]
produces again [1.0, 2.3, 1.2]

Also lookup the documentation for numpy.reshape. With this you could provide a 
single list of for example 9 numbers and reshape it into a 3x3 array.

Python and Numpy are so cool!!

Marco
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Re: Python on Windows

[Marco Nawijn]

On Tuesday, October 16, 2012 1:29:23 PM UTC+2, graham wrote:
 Downloaded and installed Python 2.7.3 for windows (an XP machine).
 
 
 
 Entered the Python interactive interpreter/command line and typed the 
 
 following:

 
 
   import feedparser
 
 
 
 and I get the error message No module named feedparser.
 
 
 
 There is a feedparser.py file lurking around - so I suppose Python 
 
 cannot find it.
 
 
 
 Anyone: What to do?
 
 
 
 
 
 
 
 GC
Hi,

feedparser.py is not a Python standard library. So, if it feedparser is located 
in a non-standard folder you have at least the following two options:
1. Update the PYTHONPATH environment variable such that it includes the path 
the installation location of feedparser.py

2. Add the path to feedparser.py directly in the script that uses it. Something 
like the following:
import sys
sys.path.append(path to feedparser.py)

import feedparser

Regards,

Marco
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Re: Providing a Python wrapper to a C++ type.

[Marco Nawijn]

On Tuesday, October 16, 2012 1:39:44 PM UTC+2, Stefan Behnel wrote:
 Marco Nawijn, 16.10.2012 12:17:
 
  On Tuesday, October 16, 2012 10:11:52 AM UTC+2, aaron.l...@gmail.com wrote:
 
  I have a C++ module where I have a defined, working type. How would I
 
  make a wrapper for this type to be able to be used in Python? I am
 
  familiar(-ish) with the C-API for functions but I can't see concretely how
 
  one would include an interface to a type.
 
 
 
  Is it this? http://docs.python.org/release/2.7.3/extending/newtypes.html
 
  
 
  There are a few ways of doing this. At least three come to my mind:
 
  1. Wrap the C++ type yourself by using handcrafted code implemented with 
  the Python C API
 
  2. Use SWIG to wrap the C++ code and (semi) automatically create the 
  wrapper (http://www.swig.org/)
 
  3. Use BOOST Python to wrap the C++ code 
  (http://www.boost.org/doc/libs/1_51_0/libs/python/doc/index.html)
 
  
 
  I would highly discourage (1) unless you are very brave and curious. 
  Ofcourse it is a nice excercise, but if you want something to work quickly 
  I would recommend to use either (2) or (3).
 
  
 
  I have used both SWIG and BOOST Python and either of them worked pretty 
  well for me. In the end I selected BOOST Python, because I was only 
  interested in the Python wrapping (SWIG could generate many other wrappers 
  as well).
 
 
 
 There's also Cython, which provides a very flexible way (unlike SWIG) of
 
 doing these things easily (unlike C++ with Boost).
 
 
 
 http://docs.cython.org/src/userguide/wrapping_CPlusPlus.html
 
 
 
 I agree with discouraging 1) in specific.
 
 
 
 Stefan

Hi Stefan,

I never worked with Cython (but I know it is very powerful and interesting) but 
in my mind there are slight differences in usage scenario between e.g. Boost 
Python and Cython. For me the idea of Cython is that your main code is in 
Python, but you want to improve the performance of specific parts of the code. 
In that case, Cython is the way to go. In case of Boost Python, the scenario 
for me is that you have a main program/library in C++, but you want to be able 
use the functionality from Python. 

Do you agree with this view?

Marco
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Re: python CAD libraries?

[Marco Nawijn]

On Monday, September 10, 2012 11:10:55 PM UTC+2, Jayden wrote:
 Are there any python CAD libraries that can
 
 
 
 (1) build simple 3D primitives solids such as spheres, cylinders and so on
 
 (2) perform bool operations on 3D solids
 
 (3) better if it has some transformations such has scaling, sweeping, and 
 lofting
 
 
 
 Please recommend some good ones for me? Thanks a lot!!

Hi Jayden,

In my opinion, the best you can get is OpenCascade (OCC) (www.opencascade.org) 
in combination with the python bindings (www.pythonocc.org). OCC is a hugh C++ 
CAD library. It not only deals with the simple geometric stuff, but it can be 
used to build CAD programs similar to SolidEdge or SolidWorks. It does however 
come with quite a steep learning curve. When using PythonOCC, the learning 
curve becomes a little less steep. 

Also note that in my opinion, Blender cannot be considered as a CAD 
environment. Ofcourse it is very powerful, but I think it is more targeted 
towards animation and visually pleasing applications, not mechanical 
engineering.

Regards,

Marco
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Re: pythonOCC examples doesn't work?

[Marco Nawijn]

On Wednesday, September 12, 2012 6:02:14 AM UTC+2, Jayden wrote:
 I installed 
 
 (1) pythonxy2.7.2.3 (with python2.7) and 
 
 (2) pythonOCC-0.5-all-in-one.win32.py26 
 
 on windows 7 64 bit computer. 
 
 
 
 I try run pythonOCC examples in its example folder, such as the helloworld.py 
 and got errors as follows: 
 
 
 
 ImportantError: DLL load failed: The specified module could not be found. 
 
 
 
 The error come from the line of code: 
 
 
 
 from OCC.BrepPrimAPI import * 
 
 
 
 How to fix the error? Thanks a lot!!

Hi Jayden,

It has been some time ago that I used PythonOCC and I used it on Linux, so I 
cannot be of much help here. It sounds like you have to tell Windows where to 
look for the installed libraries (environment variables?). Anyhow, I recommend 
to post the question to the PythonOCC mailinglist. They are quite responsive.

One last suggestion. OCC itself comes with a small utility called DRAWEXE. It 
is a tcl/tk program that can be used to play around with a lot of the 
functionality provided by OCC.

Good luck!

Marco
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Re: Looking for an IPC solution

[Marco Nawijn]

On Friday, August 31, 2012 9:22:00 PM UTC+2, Laszlo Nagy wrote:
 There are just so many IPC modules out there. I'm looking for a solution 
 
 for developing a new a multi-tier application. The core application will 
 
 be running on a single computer, so the IPC should be using shared 
 
 memory (or mmap) and have very short response times. But there will be a 
 
 tier that will hold application state for clients, and there will be 
 
 lots of clients. So that tier needs to go to different computers. E.g. 
 
 the same IPC should also be accessed over TCP/IP. Most messages will be 
 
 simple data structures, nothing complicated. The ability to run on PyPy 
 
 would, and also to run on both Windows and Linux would be a plus.
 
 
 
 I have seen a stand alone cross platform IPC server before that could 
 
 serve channels, and send/receive messages using these channels. But I 
 
 don't remember its name and now I cannot find it. Can somebody please help?
 
 
 
 Thanks,
 
 
 
 Laszlo

Hi,

Are you aware and have you considered zeromq (www.zeromq.org)? It does not 
provide a messaging system, but you could use things like simple strings (json) 
or more complicated things like Protobuf. 

Marco 
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Re: Beginners question

[Marco Nawijn]

On Thursday, August 30, 2012 1:54:08 PM UTC+2, (unknown) wrote:
 Hello
 
 
 
 I'm slowly teaching myself python so apologies if this is a dumb question.
 
 but something has confused me with the os.stat() function:
 
 
 
  s = os.stat(.)
 
  print s
 
 posix.stat_result(st_mode=16877, st_ino=2278764L, st_dev=2053L, st_nlink=2, 
 st_u
 
 id=1000, st_gid=100, st_size=4096L, st_atime=1346327745, st_mtime=1346327754, 
 st
 
 _ctime=1346327754)
 
 
 
 What sort of object is posix.stat_result? Its not a dictionary or list or a 
 
 class object as far as I can tell. Thanks for any help.
 
 
 
 B2003

Hi,

So let's try to figure this out. First of all, we can ask Python what object it 
is.

 s = os.stat('.')
 type(s)
posix.stat_result

So it seems to be a custom type. However types can inherit from builtins like
list, tuple and dict, so maybe it still is a dict or a tuple. Let's ask Python 
again:

 isinstance(s, dict)
False
 isinstance(s, (tuple, list))
False

Ok. So it is neither a list (tuple) nor a dict. So without reverting to the 
source code, it is probably save to say that the result is a custom class where 
the attributes can be accessed by the dot '.' notation. This is confirmed when 
you do:

 dir(s)
..
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 'n_fields',
 'n_sequence_fields',
 'n_unnamed_fields',
 'st_atime',
 'st_blksize',
 'st_blocks',
 'st_ctime',
 'st_dev',
 'st_gid',
 'st_ino',
 'st_mode',
 'st_mtime',
 'st_nlink',
 'st_rdev',
 'st_size',
 'st_uid']

For example:

 print s.st_size
4096

In case of Linux I think that the result of os.stat(..) is a wrapping of a C 
struct (a class with only attributes and no methods).

A small additional remark. Besides being a real dict or list (by means of 
inheritance), custom class can also implement the interface (__getitem__ etc.). 
If you want to know if an object implements this interface you could use the 
types defined in the 'abc' and 'collections' standard modules. So instead of 
checking if a type is a dict like this:

 isinstance(s, dict)

you could also check if it implements the dict interface:

 isinstance(s, collections.MutableMapping) # or similar

Regards,

Marco
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Re: class object's attribute is also the instance's attribute?

[Marco Nawijn]

On Thursday, August 30, 2012 12:55:25 PM UTC+2, 陈伟 wrote:
 when i write code like this:
 
 
 
 class A(object):
 
  
 
 d = 'it is a doc.'
 
 
 
 
 
 t = A()
 
 
 
 print t.__class__.d
 
 print t.d
 
 
 
 the output is same.
 
 
 
 so it means class object's attribute is also the instance's attribute. is it 
 right? i can not understand it.

I think the best way is to think of it as a global attribute restricted to the 
class A. Note that you even don't need an instance to get the value of the 
attribute. You can directly get it from the class itself.

 class A(object): d = 'my attribute'
 A.d
'my attribute'
 aobj = A()
 aobj.d
'my attribute'

Note that if you change 'd' it will change for all instances!
 bobj = A()
 bobj.d
'my attribute'

 A.d = 'oops...attribute changed'
 aobj.d
'oops...attribute changed'

 bobj.d
'oops...attribute changed'

If you want attributes to be local to the instance, you have to define them in 
the __init__ section of the class like this:

class A(object):

   def __init__(self):
d = 'my attribute'

 aobj = A()
 bobj = A()

 aobj.d
'my attribute'

 bobj.d
'my attribute'

 aobj.d = 'oops...attribute changed'

 aobj.d
'oops...attribute changed'

 bobj.d
'my attribute'

Regards,

Marco
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Re: Beginners question

[Marco Nawijn]

On Thursday, August 30, 2012 3:15:03 PM UTC+2, Ulrich Eckhardt wrote:
 Am 30.08.2012 13:54, schrieb boltar2003@boltar.world:
 
  s = os.stat(.)
 
  print s
 
  posix.stat_result(st_mode=16877, st_ino=2278764L, st_dev=2053L, st_nlink=2, 
  st_u
 
  id=1000, st_gid=100, st_size=4096L, st_atime=1346327745, 
  st_mtime=1346327754, st
 
  _ctime=1346327754)
 
 
 
  What sort of object is posix.stat_result?
 
 
 
 Use the type() function to find out. I guess that this is a named tuple, 
 
 which is a tuple where the attributes are not indexed but have a name, 
 
 see the documentation for the namedtuple() function from the collections 
 
 library.
 
 
 
 Uli

It is not a namedtuple. Because a namedtuple is a tuple and therefore 
isinstance(s, tuple) would have returned True.

 from collections import namedtuple
 Point = namedtuple('Point', 'x y')
 p = Point(10,2)
 isinstance(p, tuple)
True
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Re: class object's attribute is also the instance's attribute?

[Marco Nawijn]

On Thursday, August 30, 2012 3:25:52 PM UTC+2, Hans Mulder wrote:
 On 30/08/12 14:34:51, Marco Nawijn wrote:
 
 
 
  Note that if you change 'd' it will change for all instances!
 
 
 
 That depends on how you change it.
 
 
 
  bobj = A()
 
  bobj.d
 
  'my attribute'
 
  
 
  A.d = 'oops...attribute changed'
 
 
 
 Here you change the attribute on the class.
 
 That will affect all instances:
 
 
 
  aobj.d
 
  'oops...attribute changed'
 
  
 
  bobj.d
 
  'oops...attribute changed'
 
 
 
 You can also set the attribute on an instance:
 
 
 
  bobj.d = 'For bobj only'
 
  bobj.d
 
 'For bobj only'
 
  aobj.d
 
  'oops...attribute changed'
 
 
 
 So, if you specifically change it on one instance, thenit won't
 
 change on other instances of the same class.
 
 
 
  If you want attributes to be local to the instance, you have
 
  to define them in the __init__ section of the class like this:
 
 
 
 That's a good idea, but it's not required.  You can set them
 
 later, as shown above.
 
 
 
 
 
  class A(object):
 
  
 
 def __init__(self):
 
  d = 'my attribute'
 
 
 
 That will just set the global variable d.
 
 You want to set the instance attribute:
 
 
 
 self.d = 'my attribute'
 
 
 
  aobj = A()
 
  bobj = A()
 
  
 
  aobj.d
 
  'my attribute'
 
 
 
 Note that aobj.d will not find the global variable d,
 
 if neither the instance, nor the class nor any of the
 
 base classes have that attribute.
 
 
 
 I don't know where this 'my attribute' comes from, but
 
 it's not the instance attribute you tried to set in the
 
 __init__ method.  Maybe your class A still has a class
 
 attribute with that value from an earlier experiment.
 
 
 
 
 
 Hope this helps,
 
 
 
 -- HansM

Learned my lesson today. Don't assume you know something. Test it first ;). I 
have done quite some programming in Python, but did not know that class 
attributes are still local to the instances. It is also a little surprising I 
must say. I always considered them like static variables in C++ (not that I am 
an expert in C++). 

I knew of course that you don't have to define a local attribute in the 
__init__ method of a class, but I consider it good style and since the OP is a 
self claimed newbie I left out the other option. 

The missing self in the code below was a typo
class A(object): 
 
def __init__(self): 
d = 'my attribute'   # should be self.d 

Regards,

Marco
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Re: class object's attribute is also the instance's attribute?

[Marco Nawijn]

On Thursday, August 30, 2012 4:30:59 PM UTC+2, Dave Angel wrote:
 On 08/30/2012 10:11 AM, Marco Nawijn wrote:
 
  On Thursday, August 30, 2012 3:25:52 PM UTC+2, Hans Mulder wrote:
 
  snip
 
 
 
  Learned my lesson today. Don't assume you know something. Test it first ;). 
  I have done quite some programming in Python, but did not know that class 
  attributes are still local to the instances. 
 
 
 
 They're not.  They're just visible to the instances, except where the
 
 instance has an instance attribute of the same name.  Don't be confused
 
 by dir(), which shows both instance and class attributes.
 
 
 
 Please show me an example where you think you observe each instance
 
 getting a copy of the class attribute.  There's probably some other
 
 explanation.

I don't have an example. It was just what I thought would happen. Consider the 
following. In a class declaration like this:

class A(object):
attr_1 = 10

def __init__(self):
   self.attr_2 = 20

If I instantiated it twice:

obj_1 = A()
obj_2 = A()

For both obj_1 and obj_2 attr_1 equals 10. What I thought would happen after 
the following statement:

obj_1.attr_1 = 12

is that obj_2.attr_1 also equals 12. This is what surprised me a little, that's 
all. 

Marco
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Re: dynamically creating classes from text

[Marco Nawijn]

On Jan 24, 6:22 pm, T H turian9...@gmail.com wrote:
 I’m new to python, sorry if my question is a bit naive, I was
 wondering if it is possible to parse some text (ie. from a text file
 or say html) and then dynamically create a class?

 for example lets say the contents of the text file is:

      functionName: bark  arg1: numberBarks
      functionName: run    arg1: howFast  arg2: howLong

 and then from the text dynamically create a class like the one below
 (including the functions and its implementation)

 class Dog:
         def bark(self, numberBarks, myArg):
                 print(‘numberBarks: ‘ + numberBarks)
                 print(‘myArg’ + myArg)
                 return
         def run(self, howFast, howLong, myArg):
                 print(‘howFast: ‘ + howFast)
                 print(‘howLong’ + howLong)
                 print(‘myArg’ + myArg)
                 return

 I know my question is a bit far fetched. Anyhow if it is possible how
 is it done?
 Thanks so much for any help!

Hi,

You could also take a look at the 'type' builtin. It can be used to
dynamically create a class. It allows you to specify the class name,
the bases and a dictionary containing the attributes. A simple
example:

 aClass = type('A', (object, ), { 'a' : 10, 'b' : 'Hello World' })
 aobj = aClass()
 aobj.__class__.__name__
'A'
 aobj.a
10

The methods might be a little more difficult to attach to the class,
but I don't fully understand your problem. In particular, where does
the implementation of your methods come from?

Marco

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Re: Multiprocessing bug, is my editor (SciTE) impeding my progress?

[Marco Nawijn]

On Dec 6, 8:13 pm, John Ladasky lada...@my-deja.com wrote:
 Hi, folks,

 Back in 2002, I got back into programming after a nine-year hiatus.  I
 needed a new programming language, was guided to Python 2.2, and was
 off to the races.  I chose the SciTE program editor, and I have been
 using it ever since.  I'm now using Python 2.6 on Ubuntu Linux 10.10.

 My programming needs have grown more sophisticated, but I'm still
 using SciTE.  Pretty much all of my recent posts to comp.lang.python
 have concerned multiprocessing.  I put together a decent system for my
 current project, and had it all working.  Then I realized that I
 needed to refactor and expand some code, which I did -- and somehow, I
 generated a bug that I simply cannot understand.  I've been puzzling
 over it for three days.

 The error is occurring inside one of my subprocesses.  As far as I
 know, SciTE is limited in what it can do in this situation.  The
 program does not return when a subprocess generates an exception.  I
 see the error message, but then the program simply hangs.

 I have tried invoking the subprocess directly without scheduling it
 through multiprocessing.Pool.  It works fine.  So the problem is
 occurring inside Pool.

 I tried opening my code in IDLE, and figured I could step through it,
 or at least call functions one line at a time.  It appears that
 multiprocessing code is not compatible with IDLE.  IDLE simply crashes
 when I try to invoke any of the important functions.

 I know, you want me to post a minimal example.  Most of the time,
 that's possible, and I do it.  Trust me, this time it isn't.  I have
 about 500 lines of code, split across three files.  These implement a
 neural network, some test data, and multiprocessing methods for
 network evaluation.  I made several concerted changes to the code, and
 turned a working system into this:

 =

 Exception in thread Thread-1:
 Traceback (most recent call last):
   File /usr/lib/python2.6/threading.py, line 532, in
 __bootstrap_inner
     self.run()
   File /usr/lib/python2.6/threading.py, line 484, in run
     self.__target(*self.__args, **self.__kwargs)
   File /usr/lib/python2.6/multiprocessing/pool.py, line 225, in
 _handle_tasks
     put(task)
 TypeError: expected string or Unicode object, NoneType found

 =

 Here's what I think would help me debug this error: I would like to
 catch the TypeError, and examine the contents of task.  I need to
 accomplish this WITHOUT adding a try...except block to the Python
 library file multiprocessing/pool.py.  I don't know whether this is
 possible, because the traceback isn't clear about where my OWN code
 calls the code which is generating the error.

 After that, if the cause of the error still is not obvious, I might
 need to go back to the working program.  Somehow I want to examine the
 contents of task when the program works, and no TypeError is being
 generated.  By comparing the two, I hope to see a difference.  From
 that, I should be able to figure out how I have broken what is being
 fed to Pool.__init__ and/or MapResult.__init__.

 Any suggestions how I might best accomplish this task?  Does this
 error message look familiar to anyone?

 More generally, should I consider graduating from SciTE?  I have had a
 look at a few of the more comprehensive IDE's over the years, and I'll
 have to say that I found them to be intimidating.  I found it to be a
 huge chore just to open a single Python script and run it inside an
 IDE.  It seems like you had to know how to set up a complete, multi-
 script project before you could even accomplish simple tasks.  That
 steep learning curve is the reason that I didn't choose Java as my
 programming language.

 So, if any of you have pertinent recommendations in the IDE
 department, please feel free to guide me that way.

 Thanks!
Hello John,

One way of trying to debug the issue could be to use ipython and ipdb.
You cadn than run your code from within the ipython shell. The
debugger will hold at the type error, but keep the context. At this
point you should be able to evaluate task.

As a side comment to your IDE remarks. I keep switching between VIM
and Aptana/Pydev. The more I learn about VIM the more I feel
comfortable and productive. In combination with ipython it is quite a
solid development environment. On the other hand Pydev is very user
friendly, powerfull and easy to learn. Debugging in Pydev is
excellent.

Regards,

Marco
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Re: Execute a command on remote machine in python

[Marco Nawijn]

On Nov 15, 1:04 pm, Roark suha...@gmail.com wrote:
 Hi,

 I am first time trying my hands on python scripting and would need
 some guidance from the experts on my problem.

 I want to execute a windows command within python script from a client
 machine on a remote target server, and would want the output of the
 command written in a file on client machine. What is the way it could
 be achieved.

 Thanks in advance,
 Roark.


Hello Roark,

If the command does not change over time, an option could be to
encapsulate the command and the output behind an XML-RPC interface. I
used it several times now and for me this works perfectly. XML-RPC is
part of the Python standard library, so it should work out of the box
on windows and linux. It also supports mixed programming languages
(maybe C# on windows to get the info you want and python on linux on
the client).

Kind regards,

Marco
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Re: Python ORMs Supporting POPOs and Substituting Layers in Django

[Marco Nawijn]

On Nov 5, 9:11 pm, Travis Parks jehugalea...@gmail.com wrote:
 Hello:

 A new guy showed up at work a few weeks ago and has started talking
 about replacing a 6 month old project, written in ASP.NET MVC, with an
 open source solution that can handle massive scaling. I think his
 primary concern is the potential need for massive web farms in the
 future. In order to prevent high licensing costs, I think he wants to
 move everything to open source technologies, such as the LAMP stack. I
 also don't think he truly understands what ASP.NET MVC is and thinks
 it is the older WebForms.

 I have been researching open source MVC frameworks and came across
 Django. It looks like an awesome tool, but I am willing to look at
 others. I have experience in Python (and enough in PHP to want to
 avoid it and absolutely none in Ruby) so I think it would be a good
 language to develop in.

 I was wondering if there were any ORMs for Python that used POPOs
 (plain old Python objects). There is a lot of business logic in my
 system, and so I want to keep my data objects simple and stupid. I
 want the ORM to be responsible for detecting changes to objects after
 I send them back to the data layer (rather than during business layer
 execution). Additionally, being a stateless environment, tracking
 objects' states isn't very useful anyway.

 Honestly, I doubt this guy is going to get his wish. The people paying
 for the application aren't going to be willing to throw 6 months of
 work down the drain. Never the less, I want to have plenty of research
 under my belt before being asked what my thoughts are. He was talking
 about using the Zend Framework with PHP, but I want to avoid that if
 possible. Django seems like one of the best MVC solutions in the
 Python arena. I would be willing to replace Django's ORM solution with
 something else, especially if it supported POPOs. I could even map all
 of the non-POPOs to POPOs if I needed to, I guess.

 Finally, I wanted to ask whether anyone has tried having Django call
 out to Python 3 routines. I am okay using Python 2.7 in Django, if I
 can have the controllers call business logic implemented in Python 3,
 accepting POPOs from the data layer. Django would really just be a
 coordinator: grab data from Django ORM, convert results into POPOs,
 load up Python 3 module with business logic, passing POPOs, returning
 POPOs and then converting those to view models. I'm sweating just
 thinking about it. My guess is that there would be a severe penalty
 for crossing process boundaries... but any insights would be
 appreciated.

 Thanks,
 Travis Parks

Hello Travis,

I am not an expert in the field,  but I have used SQLAlchemy
(www.sqlalchemy.org)
for a while and was very happy with it. It should be able to scale up
to pretty
complex applications and large amounts of data.

Regards,

Marco
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Re: Tree structure

[Marco Nawijn]

On Jul 26, 6:53 am, Bevan Jenkins beva...@gmail.com wrote:
 Hello,

 I am trying to create a tree structure for use with a PyQt QTreeView.
 But first I need to get my head around how to create the tree
 structure.  I have a dictionary (for testing purposes) but I will
 later use a table via sqlalchemy.

 The use case is hydrology, so I  would like to have a hydrologically
 connected river tree, in which you can browse upstream from the sea
 (making choices) or downstream from any named hydrological feature.
 Each key flows into its value pair. myrivers =
 {river:flows_into}.  An example is below:

 myrivers = {little stream:sea,
     mountain stream:lake,
     lake:big river,
     cold spring:big river,
     big river:sea
     sea:}

 I would like the tree to look like (if the formatting works). so
 you can browse downstream from each named river but also upstream from
 the sea picking which direction to go.

 little stream
     sea
 mountain stream
     lake
         big river
             sea
 lake
     big river
         sea
 cold spring
     big river
         sea
 big river
     sea
 sea
     little stream
     big river
         lake
             mountain stream
         cold spring

 this next part is probably not very clear
 So every key is a parent.  For all keys that have a value (not ),
 the value is the child and is then used as a parent to get the next
 child until the sea and a value of  is reached.  For the sea this is
 reversed, that you find all rivers that flow into the sea and then all
 rivers that flow into them.

 Any thoughts about how to acomplish this will be much appreciated,
 Bevan

Hello Bevan,

Is it an option to use XML as an in-memory representation. It
naturally provides the
interface you need, like traversing from parent to children and back.
In addition, you
get querying capabilities like XPATH for free. In python I recommend
lxml.

Your task than is to fill the tree based on the information in the
database. The ORM functionality
from sqlalchemy will be of help here. In addition, you somehow have to
populate the QT tree with the
data from your in-memory XML representation. I have no experience with
QT so I cannot help you there.

Regards,

Marco
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Re: losing-end-of-row values when manipulating CSV input

[Marco Nawijn]

On Jul 13, 10:22 pm, Neil Berg nb...@atmos.ucla.edu wrote:
 Hello all,

 I am having an issue with my attempts to accurately filter some data from a 
 CSV file I am importing.  I have attached both a sample of the CSV data and 
 my script.  

 The attached CSV file contains two rows and 27 columns of data.  The first 
 column is the station ID BLS, the second column is the sensor number 4, 
 the third column is the date, and the remaining 24 columns are hourly 
 temperature readings.

 In my attached script, I read in row[3:] to extract just the temperatures, do 
 a sanity check to make sure there are 24 values, remove any missing or m 
 values, and then append the non-missing values into the hour_list.  

 Strangely the the first seven rows appear to be empty after reading into the 
 CSV file, so that's what I had to incorporate the if len(temps) == 24 
 statement.  

 But the real issue is that for days with no missing values, for example the 
 second row of data, the length of the hour_list should be 24.  My script, 
 however, is returning 23.  I think this is because the end-of-row-values have 
 a trailing \. This must mark these numbers as non-digits and are lost in my 
 isdig filter line.  I've tried several ways to remove this trailing \, 
 but to no success.

 Do you have any suggestions on how to fix this issue?

 Many thanks in advance,

 Neil Berg

  csv_test.py
 1KViewDownload

  csv_sample.csv
  1KViewDownload

Dear Neil,

Don't know if this is a double post (previous post seems to be gone),
but val = val.rstrip('\\') should fix your problem. Note the double
backslash.

Kind regards,

Marco
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Re: losing-end-of-row values when manipulating CSV input

[Marco Nawijn]

On Jul 13, 10:22 pm, Neil Berg nb...@atmos.ucla.edu wrote:
 Hello all,

 I am having an issue with my attempts to accurately filter some data from a 
 CSV file I am importing.  I have attached both a sample of the CSV data and 
 my script.  

 The attached CSV file contains two rows and 27 columns of data.  The first 
 column is the station ID BLS, the second column is the sensor number 4, 
 the third column is the date, and the remaining 24 columns are hourly 
 temperature readings.

 In my attached script, I read in row[3:] to extract just the temperatures, do 
 a sanity check to make sure there are 24 values, remove any missing or m 
 values, and then append the non-missing values into the hour_list.  

 Strangely the the first seven rows appear to be empty after reading into the 
 CSV file, so that's what I had to incorporate the if len(temps) == 24 
 statement.  

 But the real issue is that for days with no missing values, for example the 
 second row of data, the length of the hour_list should be 24.  My script, 
 however, is returning 23.  I think this is because the end-of-row-values have 
 a trailing \. This must mark these numbers as non-digits and are lost in my 
 isdig filter line.  I've tried several ways to remove this trailing \, 
 but to no success.

 Do you have any suggestions on how to fix this issue?

 Many thanks in advance,

 Neil Berg

  csv_test.py
 1KViewDownload

  csv_sample.csv
  1KViewDownload

Hello Neil,

I just had a quick look at your script. To remove the trailing \ you
can use val = val.rstrip('\\') in your script. Note the double
backslash.

The script now returns 24 items in the hour_list.

Good luck!

Marco


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Re: Passing array from java to python

[Marco Nawijn]

On Jun 2, 11:54 am, loial jldunn2...@gmail.com wrote:
 I need to pass some sort of array or hashmap from Java and read the
 data in a python script (which will be called by the java class). Is
 there any neater way  to do this other than just passing strings?

I recently had to deal with the same problem, some bi-directional
communication between Java and Python. Several options were discussed
between me and my fellow programmer. In the end we settled for XML-
rpc. It works remarkably well in our case. We use it to pass test and
simulation data to GUI code. XML-rpc is very well supported in python.
Basic types (lists, dicts etc.) are encoded automatically. If the
arrays are very large, I would probably use an intermediate database
(e.g. Hdf5) for storage and then use some sort of messaging to inform
the Java code of any changes.

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Re: code structure advise for a model

[Marco Nawijn]

On Feb 4, 3:43 am, Martin De Kauwe mdeka...@gmail.com wrote:
 Hi,

 I am translating some c++ code to python and just wanted to ask some
 advise on structure. The original has everything declared globally and
 nothing passed via function (I assume, but don't know, that this isn't
 just standard c++ practice!). So given this, I have a pretty much
 clean slate as I can't quite just copy the functions over. I was
 thinking something like this

 class Params:

     def __init__(self, fname):
         self.set_inital_condtions()
         self.read_input_file(fname)

     def set_inital_conditons(self):
         self.some_parm = 0.0

     def read_input_file(fname):

         #read file, change initial params if specified

 then I thought I could pass this as an object to the model class

 class Model(Params):

     def __init__(self):
         # blah

     def some_func(self):
          if (Params.some_param == something):
              foo

 OR this just a very bad way to structure it?

 The other thing I can't decide on is how to pass the parameters and
 variables through the class. So because of the way the original is
 written (everything is global), I could just inherit things, but it
 does means there is a lot of self. syntax. So I wondered if it might
 be better to pass things as function arguments? Any thoughts? I am
 also half considering other users from non-python backgrounds and what
 might seem very alien (syntax) to them.

 thanks in advance

 (ps. I am cross posting this on comp.lang.python as I am not sure
 where is more appropriate).

I would structure it in three classes/functions:
1. A parser class/function that reads an input file and returns a
Parameters object
2. A Parameters class
3. A Model class that uses the Parameters

You would end up with something like the following:


class MyParser(object):

def __init__(self, filename=None):
self.filename = filename

def parse(self, filename):

params = Parameters()

...read info from filename and update parameters


return params

class Parameters(object):

def __init__(self):
 self.myAttribute1 = 0
 self.myAttribute2 = A string


class MyModel(object):

   def __init__(self, parameters):
   self.parameters = parameters

   def solve(self):
...solve the problem

The driver program would look something like this:

parser = MyParser()

params = parser.parse('inputfile')

model = MyModel(params)
model.solve()

I hope this is helpfull for you.

Regards,

Marco









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Re: Comparing floats

[Marco Nawijn]

On 29 nov, 00:20, Nobody nob...@nowhere.com wrote:
 On Sat, 27 Nov 2010 18:23:48 -0500, Terry Reedy wrote:
  Therefore, to implement this multiplication operation I need to have a
  way to verify that the float tuples C and D are equal.

  I might try the average relative difference:
  sum(abs((i-j)/(i+j)) for i,j in zip(C,D))/n # assuming lengths constant

 The division is unstable if i and j are close to zero.

 For scalars, I'd use:

         abs(i-j) = epsilon * (1 + abs(i+j))

 This amounts to a relative error check for large values and an absolute
 error check for values close to zero.

 For a vector, I'd check that the above holds for all pairs.

Hi All,

Why don't you treat the C and D tuples as vectors? You can than check
dot product
and norm (length) for equality. Using scipy (www.scipy.org), you even
get very nice
performance.

Marco
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Re: fast kdtree tree implementation for python 3?

[Marco Nawijn]

On 11 sep, 20:15, _wolf wolfgang.l...@gmail.com wrote:
 does anyone have a suggestion for a ready-to-go, fast kdtree
 implementation for python 3.1 and up, for nearest-neighbor searches? i
 used to use the one from numpy/scipy, but find it a pain to install
 for python 3. also, i'm trying to wrap the code 
 fromhttp://code.google.com/p/kdtree/
 using cython, but i'm still getting errors.

 i wish stuff like kdtree, levenshtein edit distance and similar things
 were available in the standard library.

Do you know about the kdtree implementation in biopython? I don't know
if it is already available for Python 3, but for me it worked fine in
Python 2.X.

Marco
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Re: Processing HTML form

[Marco Nawijn]

On 17 jun, 21:11, Bradley Hintze bradle...@aggiemail.usu.edu wrote:
 Hi,

 I am a newbie to anything web related, I know a bit  of HTML though.
 I've been programing in python for a year or so so I know the language
 at an intermediate level. I am wondering if its possible to get info
 from an HTML form and pass it to my python code and return a page
 based on  the code executed. All of my web searches have been
 fruitless as I quickly get lost in the jargon and perhaps not sure
 what phrase i should search. Any help would be appreciated.

 Thank you,
 Bradley

Hi Bradley,

If I understand correctly, you want to do the following:
   1. Fill in a HTML form in a client (web browser)
   2. Send the form to a webserver
   3. Have the webserver extract the information from the form
   4. Send the information to a python program for processing
   5. Generate a new HTML page in python based on the information in
step 4
   6. Send the newly generated page back to the client

Possible solutions depend a little on the constraints and/or options
you have for the webserver. If you are free in your choices I would
suggest to start with cherrypy (www.cherrypy.org) for a webserver. It
is simple to start with, very powerfull and well documented. This
would cover steps 3 and 4. For step 5 I suggest you either use the
python builtin string template facility string.Template (for simple
things). If you want more power have a look at Genshi 
http://genshi.edgewall.org.

The two options I mention above help you to understand whats going on.
If you feel comfortable with this, you can take a look at python web
frameworks like Django or Turbogears (or many others).

Good luck and keep us posted with what your progress.

Regards,

Marco
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Re: Convert .doc to .pdf

[Marco Nawijn]

On 14 jun, 13:19, Thales thales@gmail.com wrote:
 Good morning,

 I need to convert some files from .doc to .pdf. I've googled it a
 little bit and all the solutions I've found used the OpenOffice API,
 but I can't use it.

 Anybody knows a library that I can use to do it?

 Thanks

What about using the win32 API and use the free  PDFCreator (http://
sourceforge.net/projects/pdfcreator/) PDF printer?

This should be very simple (code untested, but should be roughly OK):
- Instantiate MS/Word application
   from win32com.client import Dispatch
   app = Dispatch('Word.Application')
- Open your document
   doc = app.Documents.Open(demo.doc)
- Print to PDF
   app.ActivePrinter = PDFCreator
   app.PrintOut()

The PrintOut call is a little tricky. I normally try to decode and
guess the Python call from the corresponding VisualBasic code I record
with the macro recording facility. I know there are more sophisticated
methods out there, but I never tried them.

Regards,

Marco
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Re: Convert .doc to .pdf

[Marco Nawijn]

On 14 jun, 17:55, Thales thales@gmail.com wrote:
 On 14 jun, 11:01, Marco Nawijn naw...@gmail.com wrote:





  On 14 jun, 13:19, Thales thales@gmail.com wrote:

   Good morning,

   I need to convert some files from .doc to .pdf. I've googled it a
   little bit and all the solutions I've found used the OpenOffice API,
   but I can't use it.

   Anybody knows a library that I can use to do it?

   Thanks

  What about using the win32 API and use the free  PDFCreator (http://
  sourceforge.net/projects/pdfcreator/) PDF printer?

  This should be very simple (code untested, but should be roughly OK):
  - Instantiate MS/Word application
     from win32com.client import Dispatch
     app = Dispatch('Word.Application')
  - Open your document
     doc = app.Documents.Open(demo.doc)
  - Print to PDF
     app.ActivePrinter = PDFCreator
     app.PrintOut()

  The PrintOut call is a little tricky. I normally try to decode and
  guess the Python call from the corresponding VisualBasic code I record
  with the macro recording facility. I know there are more sophisticated
  methods out there, but I never tried them.

  Regards,

  Marco

 Thanks for your help Marco, but it has to work on linux, not on
 windows. Is possible to import this win32com on linux systems? How?

 Thank you!

Nope. The win32 related packages only work on Windows systems.

Maybe Wine is an option? So running a genuine MS Office under Wine on
Linux?
Otherwise, your best bet is still OpenOffice (although you mention you
cannot use it)

Regards,

Marco
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Re: using reverse in list of tuples

[Marco Nawijn]

On Jun 10, 2:39 am, james_027 cai.hai...@gmail.com wrote:
 hi,

 I am trying to reverse the order of my list of tuples and its is
 returning a None to me. Is the reverse() function not allow on list
 containing tuples?

 Thanks,
 James

As the others already mentioned list.reverse() is in-place, just as
for
example list.sort(). Alternatively, use the builtin reversed() or
sorted()
functions to get a return value (they will leave the original list
unmodified.

Example:
 a = range(3)
 b = reversed(a)
 for item in b:
  ...print item
This will produce:
  2
  1
  0

Note that reversed returns an iterator.

Marco
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Re: Microsoft Office Word and Python (Win XP)

[Marco Nawijn]

On Jan 9, 4:12 pm, 3lvss0...@gmail.com 3lvss0...@gmail.com wrote:
 Hi.
 Im very new with python. I have got some answer on my issue to use
 interop or COM ''plugins'' to access MS Word through python but i
 don't even know what those two ''plugins'' are so I cannot use them.
 What I want to do is the following:

 I need the script that moves (only moves, not change or delete!)
 entire (100% of the text) text from one .doc file to another. But its
 not so easy as it sounds. The target .doc file is not the only one but
 can be many of them. All the target .doc files are always in the same
 folder (same path) but all of them don't have the same name. The .doc
 file FROM where I want to move entire text is only one, always in the
 same folder (same path) and always with the same file name.
 Names of the target are only similar but as I have said before, not
 the same. Here is the point of whole script:
 Target .doc files have the names:
 HD1.doc
 HD2.doc
 HD3.doc
 HD4.doc
 and so on

 What I would like to have is moved the entire (but really all of the
 text, must be 100% all) text into the .doc file with the highest ( ! )
 number. The target .doc files will always start with ''HD'' and always
 be similar to above examples.
 It is possible that the doc file (target file) is only one, so only
 HD1.doc. Therefore ''1'' is the maximum number and the text is moved
 into this file.
 Sometimes the target file is empty but usually won't be. If it won't
 be then the text should be moved to the end of the text, into first
 new line (no empty lines inbetween).
 So for example in the target file which has the maximum number in its
 name is the following text:

 a
 b
 c

 In the file from which I want to move the text is:

 d

 This means I need in the target file this:

 a
 b
 c
 d

 Could someone tell me please how to do this?

 Thank you.

Hi,

I will try to head you in the right direction with the Python/MS.Word
link.

First of all, you need to install the win32 extension. See
http://sourceforge.net/projects/pywin32/

Once you have this installed you can instantiate a MS.Word application
like
this (code untested):

 from win32com.client import Dispatch
 app = Dispatch(Word.Application)
 app.Visible = True

The code so-far is more or less equivalent to opening Word without
opening
a document (normally Word will start with an empty document).

To open a document do something like the following.
 doc = app.Documents.Open(c:\\example.doc)

Further builtin Python modules that could be helpfull are:
   glob-  for searching files matching a pattern
   os, os.path -  for path related functionality like stripping
directory
   names from a complete path

Take a look at the online documentation for more information
http://docs.python.org/modindex.html

Good luck and let us know the result.

Marco
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Re: Microsoft Office Word and Python (Win XP)

[Marco Nawijn]

On Jan 9, 8:18 pm, 3lvss0...@gmail.com 3lvss0...@gmail.com wrote:
 Marco Nawijn: I have had installed pywin32 already. The three lines
 that you mentoined don't do this
I checked at my own computer and it works fine.
 also what did you mean with doc =
 app.Documents.Open(c:\\example.doc). Which document should I open
 with this line?
This was just meant as an example on how to open a Word document from
within python. This would be the basis for copying/appending from your
source
document to your target document (e.g. HD10.doc).
 It shouldn't be opened anything. I was asking about
 the script as automated process. If you know how could i do this?
Well it is a python script. So you can run it as an automated process.
You should just set app.Visible=False so the Word user interface
component
is not shown.


 Terry Reedy: I have never mentoined copying files but moving the whole
 text from, always the same (same name, same path), .doc file with.
 However copying (=moving) text to correct .doc file would be good yes.
 I know command prompt and its copy function but this way it wouldn't
 work because I would have to define the target file - the file INTO
 which I want to move the text. But I will never know the file name
 (target file). The only thing I know is:
 - the file is one of .doc files that start with HD
 - whole name of those .doc file is always HDX.doc where X is a number
 and I need to move the text into the file with maximum X (the most
 high number)
 - all the HD files will be always in the same path (same folder) but I
 would like to use the path inside the code (it might be obvious that I
 have to) because on PC and laptop, I have two different usernames and
 since HD files are located inside Documents And Settings, I have to
 use two copies of the script - one for PC, one for laptop.

 Dennis Lee Bieber: Im not familiar with python, also Im not
 programmer. Thats why Im not able to do so when people tell me do
 this then use XYZ function which will give you ZYX from what you can
 do that and you will get result. Im still willing to learn but there
 are thousands of python tutorials and the one for exsactly this topic
 probably doesn't exsist. The .doc extension is required, so I cannot
 use .txt because I need the HD files in .doc.

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Re: please help shrink this each_with_index() implementation

[Marco Nawijn]

On Jan 5, 8:58 pm, Phlip phlip2...@gmail.com wrote:
 Hypo Nt:

 def each_with_index(seq):
     index = 0
     result = []

     for item in seq:
       result.append([item, index])
       index += 1

     return result

 My Pythonic sequencing skills are obviously feeble. Can anything think
 of a way to write that in fewer lines?

 --
   Phlip
  http://c2.com/cgi/wiki?MoreliaViridis

You could use the build-in function enumerate inside a list
comprehension.

 seq = range(5)
 [ (i,s) for i,s in enumerate(seq) ]
[(0, 0), (1, 1), (2, 2), (3, 3), (4, 4)]

This will reduce the function to a one-liner.

Regards,

Marco
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Re: problems trying to build python 2.6 as a shared library

[Marco Nawijn]

On Sep 25, 1:08 pm, Chris Withers ch...@simplistix.co.uk wrote:
 Hi All,

 I'm trying to build Python 2.6 as a shared library, so I did:

    ./configure --enable-shared
    make
    make altinstall

 No obvious signs of failure, but when I try and use the resulting
 python, I get:

 python2.6: error while loading shared libraries: libpython2.6.so.1.0:
 cannot open shared object file: No such file or directory

 Why might that be?

 cheers,

 Chris

 --
 Simplistix - Content Management, Batch Processing  Python Consulting
             -http://www.simplistix.co.uk

Hello Chris,

The dynamic loader cannot find the python shared library.  There are
at least 2 options:
1. Add path that contains the shared library to the
LD_LIBRARY_PATH environment variable. In a bash shell this can be
accomplished by:  export LD_LIBRARY_PATH=/path/to/python_shared_lib:
$LD_LIBRARY_PATH
2. Add path to dynamic linker configuration file. This typically
is in '/etc/ld.so.conf'. See man page for ld for more information.

Note that I assumed that you are on a Unix/Linux machine.

Regards,

Marco
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Another form of dynamic import

[Marco Nawijn]

Hello,

In short I would like to know if somebody knows if it is possible to
re-execute a statement that raised an exception? I will explain the
reason by providing a small introduction on why this might be nice in
my case
and some example code.

I am using the python bindings to a *very* large C++ library. About
5000 classes divided over approx. 450 different
packages are exposed through the Python interface. To reduce the
number of import statements that need to be inserted and to limit the
number of wildcard imports it would be very helpful if class names
could be automatically imported from the proper module. There is no
problem in finding out the proper module given a (valid) class name.

As an example, look at the following statement

 aPoint = gp_Pnt(1.0, 0.0, 0.0) # Oops, this will raise a NameError, since
  # gp_Pnt class
is unknown

NameError: name 'gp_Pnt' is not defined

As indicated, this will raise a NameError exception. What I would like
to do is something like the following (pseudo-code):

try:


aPoint = gp_Pnt(1.0, 0.0, 0.0)[1]



except NameError, e:

 name = e.args[0].split[1]

 if isValid(name):
  doImport(name)
=== Can I go back to statement [1] from this point?
 else:
 raise e

There is no problem in catching the exception, finding out which name
is unknown to python and check if this is a valid name for my library.
My question is, is there any possibility of going back to the
statement that raised the error, re-execute the statement and
continue?

Thanks for any thoughts and suggestions.

Marco
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Re: What would you like to see in a book about Matplotlib?

[Marco Nawijn]

On Jan 5, 10:57 am, Sandro Tosi matrixh...@gmail.com wrote:
 Hello and Happy 2009!

 I received the interesting proposal to author a book on Matplotlib,
 the powerful 2D plotting library for Python.

 While preparing the arguments list, I'd like to hear even your
 opinion, because different points-of-view will lead to a better
 product.

 Some basic question I'd like to ask are:

 - what are you using matplotlib for?
 - what are the things you like the most of matplotlib, that you want
 to give emphasis to? And why?
 - what are the (basic) things that, when you were beginning to use
 matplotlib, you wanted to see grouped up but couldn't find?
 - what would you like to see in a book about matplotlib?
 - what are some those advanced feature that made you yell WOW!! ?
 - what are the things you'd like to explore of matplotlib and never
 had time to do?

 Your suggestions are really appreciated :) And wish me good luck!

Hello Sandro,

I am happy to hear that there might be a book on Matplotlib. I am
using Matplotlib for a while now and find it a very usefull and
powerfull library for generating graphs. I will try to answer some of
your questions. I am by no means an expert in the field, so I only
express my personal experience.

 What are you using matplotlib for? I currently use Matplotlib to generate a 
 series of graphs that visualise data channels (strain measurements) during a 
 structural test. These graphs need to be refreshed about every 4 seconds. 
 Each of the graphs contains 1 to 6 curves.

 What are the things you like the most of matplotlib, that you want
to give emphasis to? And why? In general I like the most the fact that
I can generate high quality publication ready graphs with a consistent
look with minimal effort. Further, although the matlab-style commands
are very usefull I think the class interface is more powerfull. The
class interface also has a steeper learning curve. So, for me it would
be very interesting if much emphasis will be on the class interface.

 What are the (basic) things that, when you were beginning to use
matplotlib, you wanted to see grouped up but couldn't find? I
seriously hope the book is not for dummies, but provides at least a
significant amount of information on more advanced features of
Matplotlib. I think the currently available tutorials are sufficient
to getting started. From my point of view I am very interested in:
- Dynamically updating a series of graphs
- Configuring layout of graphs (colors, labels, legends, etc.)
- Managing dimensions of the figure when you export the figure to
e.g PNG. For me this is interesting in the sense that if I insert a
figure in a report/paper, I would like that the fonts used in the
graph remain proportional to the surrounding text.

If you need more information please let me know.

I wish you good luck!

Kind regards,

Marco
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Re: Display the results of a query to an html table

[Marco Nawijn]

On Aug 19, 4:35 pm, Amie [EMAIL PROTECTED] wrote:
 Hi,
 how do you display the results of an sql query and display it onto the
 html form or html table

 Thanks

Hello,

You might want to take a look at:
sqlobject http://www.sqlobject.org/
or
sqlalchemy http://www.sqlalchemy.org/

These can assist in translating SQL query results into Python objects.

For generating the html forms and tables out of the sql results data
you
can try:
genshi: http://genshi.edgewall.org/
kid: http://www.kid-templating.org/

I hope this helps.

Marco
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Re: easy 3D graphics for rendering geometry?

[Marco Nawijn]

On Nov 8, 6:53 am, gsal [EMAIL PROTECTED] wrote:
 What would be the easiest way to go about offering 3D graphics for the
 purpose of rendering geometry?

 Suppose engineers (my co-workes) have to design some enclosure,
 nozzle, bracket, or whatever physical part/component, I would like to
 write a program where they can at least see the resulting geometry and
 navigate it, i.e., zoon-in/out, rotate, pan.  On the side, I could
 have data entry fields with the input parameters and when something is
 changed, the graphics can be updated immediately (after the
 necessary calculations have been done).

 I know I need to learn something, and I am willing, I just need help
 choosing what to learn.

 I don't have any experience on this matter, don't know OpenGL, Mesa,
 VTK, VRS, Maya...and all seem to have a steep learning curve. I don't
 know any of the other graphics packages more oriented for game/
 scenery/movie development (Panda, etc.), either.

 I do know my trig and build my FEA parts parametrically from points,
 to line, to surfaces, to volumes or from volume boolean algebra.

 I would like the choice to be some kind of module/API that works
 equally well on Linux as in Windows.

 So:
 What would be the easiest way?
 and would it be worth learning?
 or
 is it better to shoot for something not so easy but worth learning?

 thanks in advance for any pointers.

 gsal

Hello,

Take a look at www.opencascade.org. This is a powerfull C++ library
for building CAE
(Computer Aided Engineering) applications. It also has a rather steep
learning curve,
but the resulting geometry could be easily exported to FEA packages.

Another possibility is www.salome-platform.org which is build on top
of OpenCascade. It has
a nice Python interface which makes the learning curve probably a
little more acceptable. A
downside is that, I think there are no Windows binaries yet.

Regards,

Marco Nawijn

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Code design problem

[Marco Nawijn]

Hello,

I have a hard time figuring out an elegant and efficient design for
the following problem.

I am working on automation of structural design problems. In the
majority of cases, this boils down to executing programs in batch in
one or more loops. The scripts to control the execution differ from
fortran to bash to python and so on. Most of them are ad hoc and what
I call 'throw away scripts'. In order to improve the situation I would
like to develop a Python module that supports the execution of
external programs. Ideally I would like to make running locally or
remote trivial for the users of the module. As an example, I would
like the following (pseudo)-code to work:

app = Application('patran')# Run on local
machine
app.start(args)


app = Application('patran', host='myhost')   # Run on remote machine
app.start(args)

The problem I face is that the implementation of the application class
is completely
different for the local and remote case. The local case is a
straightforward implemenation using the subprocess module, the remote
case is a CORBA implementation. Somehow I would like to switch from
implementation class at runtime depending on whether or not the host
parameter is specified or not.

The Application, local implementation and remote implementation all
have the same interface, so a possibility might be something like the
following:

class Interface(object):
 .
 def start(self): pass
 def stop(self): pass

class LocalImplementation(Interface):
   .

class GlobalImplementation(CorbaGlobalImplementation, Interface):
   .


class Application(Interface):

  def __init__(self, program, host=None):

if host:
   self.__impl = LocalImplementation(program)
else:
   self.__impl = GlobalImplementation(program, host)

  #  Forward all methods to the implementation class
  def start(self):
  self.__impl.start()

  def stop(self):
  self.__impl.stop()


To me forwarding each call in the Application class looks a little bit
redundant and I would like to get rid of it. Does anyone have any
comments or suggestions? Can metaclass programming come to rescue?

Kind regards,


Marco Nawijn

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Re: Code design problem

[Marco Nawijn]

On Aug 29, 3:03 pm, Marshall T. Vandegrift [EMAIL PROTECTED]
wrote:
 Marco Nawijn [EMAIL PROTECTED] writes:
  The problem I face is that the implementation of the application class
  is completely different for the local and remote case. The local case
  is a straightforward implemenation using the subprocess module, the
  remote case is a CORBA implementation. Somehow I would like to switch
  from implementation class at runtime depending on whether or not the
  host parameter is specified or not.

  The Application, local implementation and remote implementation all
  have the same interface, so a possibility might be something like the
  following:

 snipped example

  To me forwarding each call in the Application class looks a little bit
  redundant and I would like to get rid of it. Does anyone have any
  comments or suggestions? Can metaclass programming come to rescue?

 It sounds like you could probably get away with just a factory function:

 def Application(program, host=None):
 if host is None:
 return LocalApplication(program)
 else:
 return RemoteApplication(program, host)

 Then just implement the same interface and/or derive from a common base
 class for LocalApplication and RemoteApplication.

 HTH!,

 -Marshall

Thanks! This makes perfect sense. (In these moments I always wonder
why I didn't come up
with this idea...)

Thanks again.

Regards,

Marco

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