date:20101006

In message mailman.1384.1286348190.29448.python-l...@python.org, Antoon 
Pardon wrote:

 A lot of times someone comes with code like the following:
 
   if len(lst) != 0:
 ...
 
 
 and than gets the advise to write it as follows:
 
   if lst:
 ...
 
 Do you mean that this second piece of code is incorrectly written ...

Yes.
-- 
http://mail.python.org/mailman/listinfo/python-list

Expression problem.

2010-10-06 Thread Nethirlon .

Hi,

I am having trouble with an expression.

I have the following line of code:

self.failUnless(c.as == 65215)

What happens when you compile this is that you get a syntax error.
This is because as has been made a keyword. failUnless is from the
module unittest.

Now my problem is this. the .as is no where defined in the code. The
code builds just fine if you removed it. But the origigal programmer
must have put it in for a reason. I just cant understand what that is.

Can anyone point me into the right direction? was .as before it
became a keyword some kind of string manipulator?

Let me know if you need more info.
Thanks
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Expression problem.

2010-10-06 Thread Chris Rebert

On Wed, Oct 6, 2010 at 1:32 AM, Nethirlon . nethir...@gmail.com wrote:
 Hi,

 I am having trouble with an expression.

 I have the following line of code:

 self.failUnless(c.as == 65215)

 What happens when you compile this is that you get a syntax error.
 This is because as has been made a keyword. failUnless is from the
 module unittest.

 Now my problem is this. the .as is no where defined in the code. The
 code builds just fine if you removed it. But the origigal programmer
 must have put it in for a reason. I just cant understand what that is.

 Can anyone point me into the right direction? was .as before it
 became a keyword some kind of string manipulator?

Nope, it was just normal attribute syntax. I would assume the original
author just named some object attribute as for whatever reason, but
the fact that removing it doesn't cause a test failure is just
bizarre. Perhaps you should examine the code for c's class (and/or its
ancestors)? (Sounds like you might have already done that though, in
which case: o_O *shrug*)

Cheers,
Chris
--
http://blog.rebertia.com
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: if the else short form

2010-10-06 Thread James Harris

On 5 Oct, 06:52, Lawrence D'Oliveiro l...@geek-
central.gen.new_zealand wrote:
 In message
 e8b46ea8-8d1e-4db9-91ba-501fd1a44...@g18g2000yqk.googlegroups.com, James

 Harris wrote:
  On 29 Sep, 18:20, Seebs usenet-nos...@seebs.net wrote:

  On 2010-09-29, Tracubik affdfsdfds...@b.com wrote:

  button = gtk.Button((False,, True,)[fill==True])

  Oh, what a nasty idiom.

  I'm surprised you don't like this construct. I hadn't seen it until I
  read the OP's question just now. However, it's meaning was immediately
  apparent.

 I’ve used it a lot, from habit because I only started heavily using Python
 with version 2.4.

 I’m still not sure I’m comfortable with “true-part if cond else false-
 part”, when just about every other language manages to standardize on
 “cond ? true-part : false-part”.

For the bit you are not comfortable with do you mean

  (false-part, true-part)[cond]

Of course, this is just an expression containing a selection.
Arbitrarily complex tests can be dealt with in languages where if
statements and case statements can be expressions. IIRC the great
Algol 60 allowed if statements to return a value. I can't say I can
see why a number of subsequent languages don't allow this.

James
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Expression problem.

2010-10-06 Thread Sebastiaan de Haan

Thank you Chris,

I'll try and find the attribute in the code. That was my conclusion
aswell... The original author must have defined it somewhere...

Thanks.

On Wed, Oct 6, 2010 at 10:59 AM, Chris Rebert c...@rebertia.com wrote:
 On Wed, Oct 6, 2010 at 1:32 AM, Nethirlon . nethir...@gmail.com wrote:
 Hi,

 I am having trouble with an expression.

 I have the following line of code:

 self.failUnless(c.as == 65215)

 What happens when you compile this is that you get a syntax error.
 This is because as has been made a keyword. failUnless is from the
 module unittest.

 Now my problem is this. the .as is no where defined in the code. The
 code builds just fine if you removed it. But the origigal programmer
 must have put it in for a reason. I just cant understand what that is.

 Can anyone point me into the right direction? was .as before it
 became a keyword some kind of string manipulator?

 Nope, it was just normal attribute syntax. I would assume the original
 author just named some object attribute as for whatever reason, but
 the fact that removing it doesn't cause a test failure is just
 bizarre. Perhaps you should examine the code for c's class (and/or its
 ancestors)? (Sounds like you might have already done that though, in
 which case: o_O *shrug*)

 Cheers,
 Chris
 --
 http://blog.rebertia.com

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

2010-10-06 Thread Chris Withers


On 06/10/2010 05:28, Dennis Lee Bieber wrote:

On Tue, 05 Oct 2010 23:54:00 -0400,fkr...@aboutrafi.net23.net
declaimed the following in gmane.comp.python.general:


plz can u convert this cpp file into python i need that badly as soon as
possible... I am new to python. I just wanna learn it


Step one... DON'T TRY TO PORT C++ to Python... the object models are
quite different.


Don't be rediculous...

Chris
--
http://mail.python.org/mailman/listinfo/python-list

Re: if the else short form

2010-10-06 Thread Antoon Pardon

On Wed, Oct 06, 2010 at 09:31:48PM +1300, Lawrence D'Oliveiro wrote:
 In message mailman.1384.1286348190.29448.python-l...@python.org, Antoon 
 Pardon wrote:
 
  A lot of times someone comes with code like the following:
  
if len(lst) != 0:
  ...
  
  
  and than gets the advise to write it as follows:
  
if lst:
  ...
  
  Do you mean that this second piece of code is incorrectly written ...
 
 Yes.

OK, but you do realise this is a minority opinion within the python
community?

-- 
Antoon Pardon
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Expression problem.

2010-10-06 Thread Peter Otten

Sebastiaan de Haan wrote:

 Thank you Chris,
 
 I'll try and find the attribute in the code. That was my conclusion
 aswell... The original author must have defined it somewhere...

Don't forget to check whether the object's class (or any of its bases) has a 
__getattr__() or __getattribute__() method.

 class A(object):
... def __getattr__(self, name):
... return 42
...
 a = A()
 a.as
  File stdin, line 1
a.as
   ^
SyntaxError: invalid syntax

Note tha you can still access such an attribute using getattr()

 getattr(a, as)
42

Peter
-- 
http://mail.python.org/mailman/listinfo/python-list

C++ vs. Python Was: Re: help!!!

2010-10-06 Thread Hans-Peter Jansen

On Wednesday 06 October 2010, 06:28:51 Dennis Lee Bieber wrote:
 On Tue, 05 Oct 2010 23:54:00 -0400, fkr...@aboutrafi.net23.net

 declaimed the following in gmane.comp.python.general:
  plz can u convert this cpp file into python i need that badly as soon
  as possible... I am new to python. I just wanna learn it

   Step one... DON'T TRY TO PORT C++ to Python... the object models are
 quite different.

I do this all the time without any adverse effects (other than being glad to 
only rarely having the need of doing it the other way around ;-)).

And the models aren't _that_ different, the syntax is.

Check yourself:
http://doc.qt.nokia.com/qtmobility-1.0/lightmaps.html vs.
http://www.riverbankcomputing.com/pipermail/pyqt/2010-October/028040.html

Pete
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: [Python-ideas] [Python-Dev] Inclusive Range

2010-10-06 Thread Antoon Pardon

On Tue, Oct 05, 2010 at 01:52:39PM -0700, Chris Rebert wrote:
 On Tue, Oct 5, 2010 at 1:31 PM, Wolfgang Rohdewald
 wolfg...@rohdewald.de wrote:
  On Dienstag 05 Oktober 2010, MRAB wrote:
   About notation, even if loved right-hand-half-open
   intervals, I would wonder about [a,b] noting it. I guess
   99.9% of programmers and novices (even purely amateur) have
   learnt about intervals at school in math courses. Both
   notations I know of use [a,b] for closed intervals, while
   half-open ones are noted either [a,b[ or [a,b). Thus, for
   me, the present C/python/etc notation is at best
   misleading. So, what about a hypothetical language using
   directly math unambiguous notation, thus also letting
   programmers chose their preferred semantics (without
   fooling others)? End of war?
 
  Dijkstra came to his conclusion after seeing the results of
  students using the programming language Mesa, which does
  support all 4 forms of interval.
 
  what was his conclusion?
 
 That right-hand-half-open intervals (i.e. a = i  b, equivalently [a,
 b) ), which are what Python uses, are to be preferred.
 (See aforelinked PDF: http://www.cs.utexas.edu/users/EWD/ewd08xx/EWD831.PDF)

The problem is that the slice notation is sometimes handy in situations where
an open interval doesn't allow easily to mark what you want.

For instance I have at one time implemted a Tree. This is a dict like structure
but it allows to visit the keys in order. Because there is an order, slice
notation can make sense. e.g. if T is a tree with names as keys, T['bea':'mike']
is a subtree where we have for each key that 'bea' = key  'mike'.

But what if I wanted a subtree where 'mike' was still included, but nothing 
further?
Or what if the keys were floats or tuples and I wanted an inclusive upper 
boundary?

And what if you needed the reverse sequence. If you start with inclusive limit,
the reverse of a = item = b is b = item = a. If the second limit is to be
exclusive the reverse of a = item  b becomes (b - 1) = item  (a - 1).

So what do you do in python, if you are given a list, a lower inclusive and an
upper exclusive limit and you have to return the reverse slice. Better don't
use L[b-1:a-1:-1], because that may result in a nasty surprise, a surprise that
could have been avoided by allowing the second limit to be inclusive.

So I don't think the results in MESA are that relevant when you are working
in an environment that is not limited to integers in upgoing sequences.

-- 
Antoon Pardon
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: meta-class review

2010-10-06 Thread Jorgen Grahn

On Wed, 2010-10-06, Ethan Furman wrote:
 MRAB wrote:
 On 06/10/2010 00:17, Ethan Furman wrote:
   [snip]
   Any comments appreciated, especially ideas on how to better handle
   class- and staticmethods
  
 I think that's a bit of overkill. The problem lies in the printing
 part, but you're spreading the solution into the rest of the
 application! (A case of the tail wagging the dog, perhaps? :-))
 
 IMHO you should just use a simple function when printing:
 
 def dash_zero(x):
 return str(x) if x else '-'
 
 '%-25s: %7s' % ('DPV Failure', dash_zero(counts['D']))

 Yes, simple is better than complex, isn't it?  :)  And certainly a *lot* 
 less code!

 Thank you for pointing that out -- hopefully my blush of embarassment 
 will fade by morning.

IMHO wrapping it in a class made much sense -- I just didn't see why
it exploded with more and more.  There are a few classes like that which
I frequently use:

a. statistics counters which are like ints, but can only be incremented
   and printed (or placed into SNMP messages, or whatever the system
   uses)

b. integers to be printed right-aligned in tables of a certain width,
   and as '-' or 'n/a' or '' when they are zero.  If they are so
   int-like that you can't do (a), then just build them on-the-fly
   when you're printing:
  
   f.write('%s: %s\n' % (name, MyFormatted(value)))

   Class MyFormatted here is very much like dash_zero above; it
   has no methods except __init__ and __str__.

I mostly do this in C++; perhaps it makes more sense in a language with
static typing, overloading and templates.

/Jorgen

-- 
  // Jorgen Grahn grahn@  Oo  o.   .  .
\X/ snipabacken.se   O  o   .
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Expression problem.

2010-10-06 Thread Nethirlon .

On 6 okt, 11:53, Peter Otten __pete...@web.de wrote:
 Sebastiaan de Haan wrote:
  Thank you Chris,

  I'll try and find the attribute in the code. That was my conclusion
  aswell... The original author must have defined it somewhere...

 Don't forget to check whether the object's class (or any of its bases) has a
 __getattr__() or __getattribute__() method.

  class A(object):

 ...     def __getattr__(self, name):
 ...             return 42
 ... a = A()
  a.as

   File stdin, line 1
     a.as
        ^
 SyntaxError: invalid syntax

 Note tha you can still access such an attribute using getattr()

  getattr(a, as)

 42

 Peter

Thank you Peter,

While searching the document I found the following code:

class Open(dpkt.Packet):
__hdr__ = (
('v', 'B', 4),
('as', 'H', 0),
('holdtime', 'H', 0),
('identifier', 'I', 0),
('param_len', 'B', 0)
)

So, I am new at programming with Python, but doing my best to grasp
the concept here. From what I am understanding is that the __hdr__ is
something that the original programmer cameup with for him self. I am
just curious as to weather the as in this piece of code is the one I
am searching for.

Thanks in advance.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: [C-API] Weird sys.exc_info reference segfault

2010-10-06 Thread Antoine Pitrou

On Tue, 05 Oct 2010 16:17:57 +0200
Jonas H. jo...@lophus.org wrote:
 
 Right now I have this minimal struct:
 
 static PyTypeObject StartResponse_Type = {
  PyObject_HEAD_INIT(PyType_Type)
  0,  /* ob_size */
  start_response,   /* tp_name */
  sizeof(StartResponse),  /* tp_basicsize */
  0,  /* tp_itemsize */
  (destructor)PyObject_FREE,  /* tp_dealloc */
  0, 0, 0, 0, 0, 0, 0, 0, 0,  /* tp_print, tp_{get,set}attr, stuff */
  start_response  /* tp_call */
 };
 
 I'm not sure about the `PyObject_HEAD_INIT` argument, but passing NULL 
 to it made `dir(obj)` crash. 

It shouldn't. Are you sure you're calling PyType_Ready in the module
initialization routine?

By the way, it is recommended to use at least Py_TPFLAGS_DEFAULT for
tp_flags.

 So does setting `GenericGetAttr` as 
 `tp_getattr`.

tp_getattr has the same signature as PyObject_GetAttrString. You're
looking for tp_getattro, which takes the attribute name as a PyObject *
rather than as a char *.

However, if you want your type to have a __dict__, what you need to do
is to have a PyObject *dict member (the name is not important, of
course), and initialize tp_dictoffset to offsetof(StartResponse, dict).
You don't have to set tp_getattr, PyType_Ready() should do the right
thing.

Regards

Antoine.


-- 
http://mail.python.org/mailman/listinfo/python-list

Re: sequence multiplied by -1

2010-10-06 Thread Albert van der Horst

In article 4ca6bd15$0$2$c3e8...@news.astraweb.com,
Steven D'Aprano  st...@remove-this-cybersource.com.au wrote:
On Fri, 01 Oct 2010 14:56:52 +0200, Antoon Pardon wrote:

 Think about the following possibility.

 Someone provides you with a library of functions that act on sequences.
 They rely on the fact that '+' concatenates.

 Someone else provides you with a library of functions that act on
 numbers. They rely on the fact that '+' provides addition.

 Now however you write your sequence like numbers or number like
 sequences one of those libraries will be useless for it.

And? So what? Sequences aren't numbers. Numbers aren't sequences. You
can't expect every library to correctly work with every data type
regardless of the polymorphism of operators.

If you have no idea what x is, you can't possibly expect to know what
function(x) does, *for any function*.

(Actually, there may be one or two exceptions, like id(x). But fewer than
you think -- even str(x) is not guaranteed to work for arbitrary types.)

If you don't know whether x is a number or a sequence, you can't know
what x.sort() will do, or math.sqrt(x), or x+x. Why single out x+x as
more disturbing than the other examples?


 -- which would it do with only one
 symbol?

 But why limit ourselves to one symbol for different kind of operations,
 to begin with?

Because the more symbols you have, the higher the learning curve to
become proficient in the language, and the more like line-noise the code
becomes. If you want APL or Perl, you know where to find them -- they're
perfectly reasonable languages, but they have made design choices that
are not Python's design choices.

We use operators, because for certain common operations it is more
convenient and natural to use infix notation than function notation. And
polymorphism is useful, because it reduces the size of namespaces and
therefore the burden on the programmer. Putting these two factors
together, instead of:

There is one more important argument.
Suppose + on a certain type of a objects generates the same type
of object.
Suppose (x+y)+z = x+(y+z) (always)
This is called associativity.

Then we can forget about the brackets.
A simple expression like
y = [1,2,3] + x + [4,5,6] + z
becomes a mess without leaning on this associativity law.

Note that concatenation is by nature associative. It is so natural
that you almost must be a mathematician to realize that.


concat_lists
concat_tuples
concat_strings
concat_bytes
add_floats
add_ints
add_rationals
add_decimals

plus mixed-operand versions of at least some of them, we have a single
symbol, +, for all of these. Arguing about whether it should be a single
operator + or two operators +  is a comparatively trivial matter. I
believe that the similarity between concatenation and addition is close
enough that it is appropriate to use one symbol for both, and likewise
between repetition and multiplication. I'm glad that Guido apparently
agrees with me.

The important thing is that manipulations are the same such
that
a += b
a += c
a += d
can be replaced by
a = b + c + d
without much thought to what a b c and + represent.
In other words reuse of the important brain resource of pattern
recognition.

--
Steven

Groetjes Albert

--
-- 
Albert van der Horst, UTRECHT,THE NETHERLANDS
Economic growth -- being exponential -- ultimately falters.
alb...@spearc.xs4all.nl =n http://home.hccnet.nl/a.w.m.van.der.horst

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: resource module returns just zeros

2010-10-06 Thread Adam Tauno Williams

On Tue, 2010-10-05 at 09:49 +1100, Cameron Simpson wrote: 
 On 04Oct2010 09:02, Adam Tauno Williams awill...@whitemice.org wrote:
 | I'm using a call to the resource module's getrusage method.  On openSUSE
 | this works, on CentOS [python26-2.6.5-3.el5] it 'works' but just returns
 | zeros for the memory utilization values.
 | resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
 | openSUSE: returns 5512
 | CentOS:   returns 0
 | Anyone know what condition causes this?  Or is there a better /
 | more-reliable way to check memory utilization of the current process?
 Long standing Linux shortcoming. man getrusage on a handy Gentoo box
 says:
   The structure definition shown at the start of this page was taken from
   4.3BSD Reno.  Not all fields are meaningful under Linux.  In Linux  2.4
   only  the fields ru_utime, ru_stime, ru_minflt, and ru_majflt are
   maintained.  Since Linux 2.6, ru_nvcsw and ru_nivcsw are  also maintained. 
   Since Linux 2.6.22, ru_inblock and ru_oublock are also maintained.
 I ran across this deficiency a few years back hoping to get some memory
 stats for some software engineeers in a former life.
 Also look in /proc - the info may be available there - I expect that's
 where a Linux ps gets a lot of info.

Yep, I went that route.

def get_rss_size():
  rss = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss * 1000
  if (rss == 0):
# NOTE: This means RSS via getrusage is not working on this system
#   So we try our fallback method or reading proc/{pid}/statm
try:
  handle = open('/proc/{0}/statm'.format(os.getpid()), 'rb')
  data = handle.read(512)
  handle.close()
  rss = int(data.split(' ')[1]) * 4000
except Exception, e:
  rss = 0
  return rss

Both the /proc and getrusage produce the same value, and that value
corresponds to what is seen in ps, top, or gnome-system-monitor.
-- 
Adam Tauno Williams awill...@whitemice.org LPIC-1, Novell CLA
http://www.whitemiceconsulting.com
OpenGroupware, Cyrus IMAPd, Postfix, OpenLDAP, Samba

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: [C-API] Weird sys.exc_info reference segfault

2010-10-06 Thread Jonas H.


On 10/06/2010 02:01 PM, Antoine Pitrou wrote:

It shouldn't. Are you sure you're calling PyType_Ready in the module
initialization routine?


Yeah. The problem was that the type struct was declared 'static' in 
another module so the changes `PyType_Ready` made to the struct weren't 
applied correctly.




By the way, it is recommended to use at least Py_TPFLAGS_DEFAULT for
tp_flags.


Thanks, but I chose not to use that flags. I don't need any.


tp_getattr has the same signature as PyObject_GetAttrString. You're
looking for tp_getattro, which takes the attribute name as a PyObject *
rather than as a char *.


Thanks again, my fault :-)

I think my problems are solved and my questions answered -- thank you so 
much for you patience!


Jonas
--
http://mail.python.org/mailman/listinfo/python-list

Re: Expression problem.

2010-10-06 Thread Peter Otten

Nethirlon . wrote:

 On 6 okt, 11:53, Peter Otten __pete...@web.de wrote:
 Sebastiaan de Haan wrote:
  Thank you Chris,

  I'll try and find the attribute in the code. That was my conclusion
  aswell... The original author must have defined it somewhere...

 Don't forget to check whether the object's class (or any of its bases)
 has a __getattr__() or __getattribute__() method.

  class A(object):

 ... def __getattr__(self, name):
 ... return 42
 ... a = A()
  a.as

 File stdin, line 1
 a.as
 ^
 SyntaxError: invalid syntax

 Note tha you can still access such an attribute using getattr()

  getattr(a, as)

 42

 Peter
 
 Thank you Peter,
 
 While searching the document I found the following code:
 
 class Open(dpkt.Packet):
 __hdr__ = (
 ('v', 'B', 4),
 ('as', 'H', 0),
 ('holdtime', 'H', 0),
 ('identifier', 'I', 0),
 ('param_len', 'B', 0)
 )
 
 So, I am new at programming with Python, but doing my best to grasp
 the concept here. From what I am understanding is that the __hdr__ is
 something that the original programmer cameup with for him self. I am
 just curious as to weather the as in this piece of code is the one I
 am searching for.

Side note: if the code you have questions about is publicly available it's 
always a good idea to give the url. I am assuming that you are referring to 
an older version to this beast:

http://code.google.com/p/dpkt/source/browse/trunk/dpkt/bgp.py

Here's where your problem was fixed/adjusted to newer Python versions:
http://code.google.com/p/dpkt/source/detail?r=51

The __hdr__ is indeed an invention of the author of the package, and is feed 
to the metaclass* of dpkt.Packet. The metaclass uses it to create __slots__ 
that are filled dynamically in Packet.__init__(). 

I recommend that you read the docstring of the Packet class

http://code.google.com/p/dpkt/source/browse/trunk/dpkt/dpkt.py

but only bother about the implementation if you cannot avoid it.
You can always have a second look after you have gained some Python 
experience.

Peter

(*) Every class in Python is an instance of its metaclass, i. e. the 
relation between metaclass and class is the same as between class and 
instance. Custom metaclasses are a powerful feature, but tend to make Python 
code harder to grasp.

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Expression problem.

2010-10-06 Thread Nethirlon .

On 6 okt, 15:25, Peter Otten __pete...@web.de wrote:
 Nethirlon . wrote:
  On 6 okt, 11:53, Peter Otten __pete...@web.de wrote:
  Sebastiaan de Haan wrote:
   Thank you Chris,

   I'll try and find the attribute in the code. That was my conclusion
   aswell... The original author must have defined it somewhere...

  Don't forget to check whether the object's class (or any of its bases)
  has a __getattr__() or __getattribute__() method.

   class A(object):

  ...     def __getattr__(self, name):
  ...             return 42
  ... a = A()
   a.as

  File stdin, line 1
  a.as
  ^
  SyntaxError: invalid syntax

  Note tha you can still access such an attribute using getattr()

   getattr(a, as)

  42

  Peter

  Thank you Peter,

  While searching the document I found the following code:

  class Open(dpkt.Packet):
          __hdr__ = (
              ('v', 'B', 4),
              ('as', 'H', 0),
              ('holdtime', 'H', 0),
              ('identifier', 'I', 0),
              ('param_len', 'B', 0)
              )

  So, I am new at programming with Python, but doing my best to grasp
  the concept here. From what I am understanding is that the __hdr__ is
  something that the original programmer cameup with for him self. I am
  just curious as to weather the as in this piece of code is the one I
  am searching for.

 Side note: if the code you have questions about is publicly available it's
 always a good idea to give the url. I am assuming that you are referring to
 an older version to this beast:

 http://code.google.com/p/dpkt/source/browse/trunk/dpkt/bgp.py

 Here's where your problem was fixed/adjusted to newer Python 
 versions:http://code.google.com/p/dpkt/source/detail?r=51

 The __hdr__ is indeed an invention of the author of the package, and is feed
 to the metaclass* of dpkt.Packet. The metaclass uses it to create __slots__
 that are filled dynamically in Packet.__init__().

 I recommend that you read the docstring of the Packet class

 http://code.google.com/p/dpkt/source/browse/trunk/dpkt/dpkt.py

 but only bother about the implementation if you cannot avoid it.
 You can always have a second look after you have gained some Python
 experience.

 Peter

 (*) Every class in Python is an instance of its metaclass, i. e. the
 relation between metaclass and class is the same as between class and
 instance. Custom metaclasses are a powerful feature, but tend to make Python
 code harder to grasp.

Peter,

Thank you very much, I did not know that the code was available
online, and also did not know that the author updated it online.

The package I was using came from the openSuse python repository,
given to me by one of the maintainers of that repository.

I am having a hard time understanding the concept of classes, so I
think that I should focus on that first, before continueing to try and
contribute.

Thank you very much for your help!

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Re: Re: How to save a binary file?

When you put the 'wb' extension you have to pass a Encode the string Python  
does not accept a string on a wb file, Python3


On Oct 6, 2010 1:01am, Chris Rebert c...@rebertia.com wrote:

 On Oct 5, 2010 8:03pm, MRAB pyt...@mrabarnett.plus.com wrote:



 On 05/10/2010 23:50, hid...@gmail.com wrote:


 I did but the mistake is: Error interpreting JPEG image file (Not a  
JPEG



 file: starts with 0x5c 0x6e)







 I think the problem is maybe in the binary code here is:





  On Oct 5, 2010 6:18pm, Jonas H. jo...@lophus.org wrote:



   On 10/05/2010 11:11 PM, hid...@gmail.com wrote:



   Hello, how i can save a binary file, i read in the manual in the IO



 area



   but doesn' t show how to save it.







   Here is the code what i am using:



   s = open('/home/hidura/test.jpeg', 'wb')



   s.write(str.encode(formFields[5]))



   s.close()





 Why are you encoding it? A JPEG file should contain the binary data,



 not a textual encoding of its bytes. The error message you got said



 that the contents of the file started with a backslash.







 If you print out, say, repr(str[ : 10]) you should get something like







 'ÿØÿà\x00\x10JFIF'.







 Try this instead:







 s = open('/home/hidura/test.jpeg', 'wb')



 s.write(str)



 s.close()







 Incidentally, 'str' is a bad name for a variable because it's the name



 of the built-in string type.





On Tue, Oct 5, 2010 at 9:53 PM, hid...@gmail.com wrote:



 I has to use repr to convert in this string: ÿØÿà\x00\x10JFIF?





No, you don't/shouldn't convert it at all. Read/use the 3 lines of



suggested code that MRAB gave:



s = open('/home/hidura/test.jpeg', 'wb')



s.write(str)



s.close()





Cheers,



Chris


-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Module loading trickery

2010-10-06 Thread Thomas Jollans

On Wednesday 06 October 2010, it occurred to Dave Angel to exclaim:
 On 2:59 PM, Thomas Jollans wrote:
  snip
  % cat a.py
  foo = 'Meh.'
  import b
  
  % cat b.py
  from a import foo
  
  print(foo)
  
  % python a.py
  Meh.
  %
 
 But there are now two modules containing separate items foo, one is
 called __main__, and the other is called a.

Good point. So let's change the example to match the intentions.

% cat a.py
foo = 'Meh.'
import b

% cat b.py
from a import foo

print(foo)

% cat main.py 
import a

% python3 main.py 
Meh.
% 


 
 The former is the script you ran, and the latter is the module imported
 by b.  Several problems could occur, including if foo were a list, and b
 appended to it, the original script wouldn't see the change.
 
 DaveA
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: if the else short form

2010-10-06 Thread BartC

James Harris james.harri...@googlemail.com wrote in message 
news:e8b46ea8-8d1e-4db9-91ba-501fd1a44...@g18g2000yqk.googlegroups.com...

On 29 Sep, 18:20, Seebs usenet-nos...@seebs.net wrote:

On 2010-09-29, Tracubik affdfsdfds...@b.com wrote:

 Hi all,
 I'm studying PyGTK tutorial and i've found this strange form:

 button = gtk.Button((False,, True,)[fill==True])

 the label of button is True if fill==True, is False otherwise.

 i have googled for this form but i haven't found nothing, so can any of
 you pass me any reference/link to this particular if/then/else form?

Oh, what a nasty idiom.

Here's the gimmick.
(False,, True,)
is a tuple.  That means you can index it.  For instance:
(False,, True,)[0]
is the string False,.

So, what is the numeric value of fill == True?  Apparently, at least
at the time this was written, it was 0 if fill was not equal to True,
and 1 if fill was equal to True.

Let me say, though, that I'm a C programmer, so I'm coming from a 
language

where the result of 0-or-1 for test operators is guaranteed, and I still
wouldn't use this in live code.  It's insufficiently legible.


I'm surprised you don't like this construct. I hadn't seen it until I
read the OP's question just now. However, it's meaning was immediately
apparent.

I should say where I'm coming from. Contrast the following C and
Python:

 text = fill == true ? True, : False,;   (C)
 text = (False,, True,)[fill == true](Python)


Surely the C should be:  fill ? True, : False,;   ?


I never liked C's ?: construct partly because it doesn't scale well.
To accept more than two options it requires the programmer to build a
small hierarchy which can be awful to read and may be best expressed
as a separate function. I'd rather have a language change a predicate
to a small integer and use that to index a set of results - and this
is exactly what the OP's tutorial does.


I use this syntax where there are two possibilities chosen according to 
condition 'a':


(a | b | c)

similar to C's ?: operator. Where there are N possibilities chosen from a 
linear set, I use:


(i | a, b, c, ... |z)  # indexed from 1, default to z

(I think from Algol68 originally.)

The difference from what the Python is doing above, is that only one of the 
possibilities is ever evaluated. Extrapolating the syntax a little, Python I 
think will evaluate all N expressions (maybe even construct the tuple), 
before choosing one.


And I'm not sure there is provision for  a default value either, without 
having a far more complex expression:


x = (One,Two,Three) [i-1]

While this works for i = 1,2,3, it goes funny for i=0,-1,-2, and generates 
an error for the rest (I'm sure Python has myriad ways of achieving this 
succinctly,  but this isn't it...)



As another hypothetical example where sgn() returns -1, 0 or +1

 position = (less, equal, greater)[sgn(a - b) + 1]



Though where the list gets much longer it would be good to be able to
label the cases for legibility.


You can do, until you want to insert an item in the middle and have to 
re-label everything...


For more complex cases I'd just use a conventional case or switch expression 
which (in my syntax at least), also evaluates just one expression, and 
returns that value. But then you can also start using if-else chains, so 
this is no longer a compact construction useful in an expression.


--
Bartc 


--
http://mail.python.org/mailman/listinfo/python-list

SAML2 support in Python

2010-10-06 Thread Roland Hedberg

Hi!

For those that are interested in making there web applications work in a SAML2 
federated environment I have two things to offer:

1) PySAML2 - a not complete but working implementation of SAML2 in Python. 
Started with implementing the SP part and are now slowly doing the IdP 
part too.

https://code.launchpad.net/~roland-hedberg/pysaml2/main

For those using Django you should take notice of what Lorenzo Gil 
Sanchez is doing using PySAML2.
https://code.launchpad.net/~lgs/pysaml2/main

2) IdPproxy - a gateway between social media and the SAML2 world.
To the SPs in a SAML2 federation it looks like a normal IdP, but it 
allows the user to authenticate using
Twitter, Facebook, Google, OpenID and Windows Live ID.
Work in progress, alpha quality.

https://code.launchpad.net/~roland-hedberg/+junk/IdPproxy

-- Roland
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Re: Re: Re: How to save a binary file?

How i get the code what MRAB says theres any manual or example?, because i  
was trying in Python2.x to do it and give me the same mistake, when i try  
to use repr that give me more backslash


On Oct 6, 2010 10:25am, hid...@gmail.com wrote:
When you put the 'wb' extension you have to pass a Encode the string  
Python does not accept a string on a wb file, Python3



On Oct 6, 2010 1:01am, Chris Rebert c...@rebertia.com wrote:
  On Oct 5, 2010 8:03pm, MRAB pyt...@mrabarnett.plus.com wrote:

  On 05/10/2010 23:50, hid...@gmail.com wrote:

  I did but the mistake is: Error interpreting JPEG image file (Not a  
JPEG


  file: starts with 0x5c 0x6e)

 

  I think the problem is maybe in the binary code here is:



   On Oct 5, 2010 6:18pm, Jonas H. jo...@lophus.org wrote:

On 10/05/2010 11:11 PM, hid...@gmail.com wrote:

Hello, how i can save a binary file, i read in the manual in the  
IO


  area

but doesn' t show how to save it.

 

Here is the code what i am using:

s = open('/home/hidura/test.jpeg', 'wb')

s.write(str.encode(formFields[5]))

s.close()



  Why are you encoding it? A JPEG file should contain the binary data,

  not a textual encoding of its bytes. The error message you got said

  that the contents of the file started with a backslash.

 

  If you print out, say, repr(str[ : 10]) you should get something like

 

  'ÿØÿà\x00\x10JFIF'.

 

  Try this instead:

 

  s = open('/home/hidura/test.jpeg', 'wb')

  s.write(str)

  s.close()

 

  Incidentally, 'str' is a bad name for a variable because it's the  
name


  of the built-in string type.



 On Tue, Oct 5, 2010 at 9:53 PM, hid...@gmail.com wrote:

  I has to use repr to convert in this string: ÿØÿà\x00\x10JFIF?



 No, you don't/shouldn't convert it at all. Read/use the 3 lines of

 suggested code that MRAB gave:

 s = open('/home/hidura/test.jpeg', 'wb')

 s.write(str)

 s.close()



 Cheers,

 Chris

-- 
http://mail.python.org/mailman/listinfo/python-list

Python shelve with a file handle

2010-10-06 Thread Adam Tauno Williams

shelve has open({filename}).  Is there anyway to open a shelve
'database' using a file handle?

Specifically I'd like to create a shelve database via a file handle
acquired from a call to SpooledTemporaryFile.

-- 
http://mail.python.org/mailman/listinfo/python-list

suggestions please what should i watch for/guard against' in a file upload situation?

2010-10-06 Thread geekbuntu

in general, what are things i would want to 'watch for/guard against'
in a file upload situation?

i have my file upload working (in the self-made framework @ work
without any concession for multipart form uploads), but was told to
make sure it's cleansed and cannot do any harm inside the system.

my checklist so far is basically to check the extension - ensure it
has 3 places, ensure it's in the allowed list (like jpg gif etc...).

not sure what else i could do to guard against anything bad
happening.  maybe the file name itself could cause greif?

not sure but any suggestions or examples are most welcome :)
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: direct print to log file

2010-10-06 Thread Sion Arrowsmith

Dave Angel  da...@ieee.org wrote:
If you want to be able to go back to the original, then first bind 
another symbol to it.

Or restore from sys.__stdout__, as long as you're sure that nothing
else has rebound sys.stdout first (or don't mind clobbering it).

-- 
\S

   under construction

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: meta-class review

2010-10-06 Thread Ethan Furman


Carl Banks wrote:

On Oct 5, 4:17 pm, Ethan Furman et...@stoneleaf.us wrote:

class DashInt(int):
 __metaclass__ = Perpetuate
 def __str__(x):
 if x == 0:
 return '-'
 return int.__str__(x)


Well, it's definitely overkill for printing a dash instead of a zero,
but a lot of people have asked how to create a subtype of int (or
other builtin) that coerces the other operand, and your idea is
interesting in that you don't have to write boilerplate to override
all the operations.

Main drawback is that it's incomplete.  For example, it doesn't coerce
properties.  int.real returns the real part of the int (i.e., the int
itself).  A subclass's real attribute should return an instance of the
subclass, but it won't.


Python 2.5.4 (r254:67916, Dec 23 2008, 15:10:54) [MSC v.1310 32 bit 
(Intel)] on win32

Type help, copyright, credits or license for more information.
 a = int()
 a
0
 a.real
Traceback (most recent call last):
  File stdin, line 1, in module
AttributeError: 'int' object has no attribute 'real'
 int.real()
Traceback (most recent call last):
  File stdin, line 1, in module
AttributeError: type object 'int' has no attribute 'real'

What am I missing here?


Another example is float.__divmod__, which
returns a tuple.  Your coercive type would fail to convert the items
of that tuple.  


Good point -- I'll get that included.


A metaclass like this I think would be possible, with
the understanding that it can never be foolproof, but it needs more
work.

Pointers:
Defining __init__ isn't necessary for this metaclass.

The len(cls_bases)  1 test can be thwarted if the base type
multiply inherits from other types itself.  The best thing to do is
handle the case of arbitrary type hierarchies, but if you don't want
to do that then the right way to catch it is to create the subtype
then check that the __mro__ is (type, base_type, object).


Thanks for the tips, Carl.

What I had wanted was to be able to specify which type(s) to look for in 
cases of multiple inheritance, but I'm not sure how to pass parameters 
to the metaclass in python2...


Can anybody shed some light on that?

Thanks!

~Ethan~
--
http://mail.python.org/mailman/listinfo/python-list

Re: suggestions please what should i watch for/guard against' in a file upload situation?

On 2010-10-06, geekbuntu gmi...@gmail.com wrote:
 in general, what are things i would want to 'watch for/guard against'
 in a file upload situation?

This question has virtually nothing to do with Python, which means you
may not get very good answers.

 my checklist so far is basically to check the extension - ensure it
 has 3 places, ensure it's in the allowed list (like jpg gif etc...).

This strikes me as 100% irrelevant.  Who cares what the extension is?

 not sure what else i could do to guard against anything bad
 happening.  maybe the file name itself could cause greif?

Obvious things:

* File name causes files to get created outside some particular
  upload directory (../foo)
* File name has spaces
* Crazy stuff like null bytes in file name
* File names which might break things if a user carelessly interacts
  with them, such as foo.jpg /etc/passwd bar.jpg (all one file name
  including two spaces).

Basically, the key question is, could a hostile user come up with
input to your script which could break something?

-s
-- 
Copyright 2010, all wrongs reversed.  Peter Seebach / usenet-nos...@seebs.net
http://www.seebs.net/log/ -- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) -- get educated!
I am not speaking for my employer, although they do rent some of my opinions.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: How to save a binary file?

2010-10-06 Thread MRAB


On 06/10/2010 15:25, hid...@gmail.com wrote:

When you put the 'wb' extension you have to pass a Encode the string
Python does not accept a string on a wb file, Python3


[snip]
You are using Python 3 and type(str) returns class 'type'?

Binary data in Python 3 should be an instance of the 'bytes' class, not
an instance of the 'str' class.

If you can't fix that, you could turn the string into bytes using:

data = bytes(ord(c) for c in str)

or by carefully choosing an encoding which would give the same result:

data = str.encode('latin-1')

Then you can save it:

s = open('/home/hidura/test.jpeg', 'wb')
s.write(data)
s.close()

I asked you to look at the result of repr so that you could see more
clearly what the data actually looked like, an instance of str or an
instance of bytes.
--
http://mail.python.org/mailman/listinfo/python-list

Re: Strong typing vs. strong testing

2010-10-06 Thread Keith H Duggar

On Sep 29, 9:01 pm, RG rnospa...@flownet.com wrote:
 That the problem is elsewhere in the program ought to be small
 comfort.  But very well, try this instead:

 [...@mighty:~]$ cat foo.c
 #include stdio.h

 int maximum(int a, int b) { return a  b ? a : b; }

 int main() {
   long x = 8589934592;
   printf(Max of %ld and 1 is %d\n, x, maximum(x,1));
   return 0;}

 [...@mighty:~]$ gcc -Wall foo.c
 [...@mighty:~]$ ./a.out
 Max of 8589934592 and 1 is 1

$ gcc -Wconversion -Werror foo.c
cc1: warnings being treated as errors
foo.c: In function 'main':
foo.c:5: warning: passing argument 1 of 'maximum' with different width
due to prototype

It's called learning to compile. And, yes, those warnings (and
nearly
every other one) should be enabled and treated as errors if a shop
wants
maximum protection. I only wish more (library) vendors did so.

KHD
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: toy list processing problem: collect similar terms

2010-10-06 Thread sln

On Sat, 25 Sep 2010 21:05:13 -0700 (PDT), Xah Lee xah...@gmail.com wrote:

here's a interesting toy list processing problem.

I have a list of lists, where each sublist is labelled by
a number. I need to collect together the contents of all sublists
sharing
the same label. So if I have the list

((0 a b) (1 c d) (2 e f) (3 g h) (1 i j) (2 k l) (4 m n) (2 o p) (4 q
r) (5 s t))

where the first element of each sublist is the label, I need to
produce:

output:
((a b) (c d i j) (e f k l o p) (g h) (m n q r) (s t))

[snip]

anyone care to give a solution in Python, Perl, javascript, or other
lang? am guessing the scheme solution can be much improved... perhaps
using some lib but that seems to show scheme is pretty weak if the lib
is non-standard.


Crossposting to Lisp, Python and Perl because the weird list of lists looks
like Lisp or something else, and you mention other languages so I'm throwing
this out for Perl.

It appears this string you have there is actually list syntax in another 
language.
If it is, its the job of the language to parse the data out. Why then do you
want to put it into another language form? At runtime, once the data is in 
variables,
dictated by the syntax, you can do whatever data manipulation you want
(combining arrays, etc..).

So, in the spirit of a preprocessor, given that the text is balanced, with 
proper closure,
ie:   ( (data) (data) )is ok.
  ( data (data) )  is not ok.

the below does simple text manipulation, joining like labeled sublists, without 
going into
the runtime guts of internalizing the data itself. Internally, this is too 
simple.

-sln
-
Alternate input:
(
  (
(0 a b) (1 c d) (2 e f )
  )
  (3 g h) (1 i j) (2 k l) (4 m n) (2 o p) (4 q r) (5 s t)
)
--
use strict;
use warnings;

my $input = EOI;
((0 a b) (1 c d) (2 e f) (3 g h) (1 i j) (2 k l) (4 m n) (2 o p) (4 q r)
 (5 s t))
EOI
my $output = $input;

my $regxout = qr/
  ( (?: \( \s* [^()]+ \s* \) (\s*) )+ )
/x;


$output =~ 
s{ $regxout }
 {
my ( $list, $format ) = ( $1, $2 );
my ( %hseen,
 @order,
 $replace
);
while ($list =~  /\(\s* (\S+) \s* (.+?) \s*\)/xsg) {
if ( exists $hseen{$1} ) {
$hseen{$1} .=  $2;
next;
}
push @order, $1;
$hseen{$1} = $2;
}
for my $id (@order) {
$replace .= ($hseen{$id}) ;
}
$replace =~ s/ $//;
$replace . $format
 }xeg;

print Input  -\n$input\n;
print Output -\n$output;

__END__

Input  -
((0 a b) (1 c d) (2 e f) (3 g h) (1 i j) (2 k l) (4 m n) (2 o p) (4 q r)
 (5 s t))

Output -
((a b) (c d i j) (e f k l o p) (g h) (m n q r) (s t))


-- 
http://mail.python.org/mailman/listinfo/python-list

SysLogHandler message formatting

2010-10-06 Thread Dustin C. Hatch

I have a daemon that uses the built-in SysLogHandler logging handler
class to log messages to the host's syslog. Unfortunately, I am having
trouble getting it to work with Metalog[1].  At first, I thought the
problem was Metalog's fault because everything works as expected with
syslog-ng. Upon further investigation, I have come to the conclusion
that the SysLogHandler may be sending invalid syslog messages. When I
disabled all filtering in Metalog, my messages started appearing in
Metalog's output logs, but they were displayed inappropriately.
Namely, the entire message was appearing where the program name should
appear. Entries in the output file generally look like this:

%b %d %H:%M:%S [%(ident)s] %(message)s

For example, here is an entry from sshd:

Oct 06 12:19:45 [sshd] Connection from 127.0.0.1 port 34142

In contrast, here is the entry generated by my program:

Oct 06 11:41:05 [INFO Started an Idler for sysattend on
mail.gosupertechs.com] 993 using SSL

Here is the snippet of code I am using to set up the logger:

root_logger = logging.getLogger()
root_logger.setLevel(config.get_value(log_level))
syslog_hdlr = SysLogHandler(address='/dev/log',
facility=SysLogHandler.LOG_DAEMON)
syslog_hdlr.setLevel(logging.DEBUG)
formatter = logging.Formatter('%(name)s: %(levelname)s %
(message)s')
syslog_hdlr.setFormatter(formatter)
root_logger.addHandler(syslog_hdlr)

logger = logging.getLogger(imapcd.daemon)
logger.debug('test')

I believe that the issue is LogRecords formatted using the Formatter
class, but are not modified into a valid syslog message. I set up a
fake syslog daemon that just listened on /dev/log and echoed
everything it received to the console. When my program logs a message,
it comes through like thist:

31imapcd.daemon: DEBUG test

which is exactly how the Formatter formatted the message. Other
programs that log to syslog, on the other hand, send messages that
look like this:

149Oct  6 11:17:19 sudo:   dhatch : TTY=pts/7 ; PWD=/home/dhatch ;
USER=root ; COMMAND=/usr/bin/whoami

If I adjust the Formatter definition to mimic that, like so:

formatter = logging.Formatter('%(asctime)s %(name)s: %(levelname)s
%(message)s', '%b %e %H:%M:%S')

then all works well.

My question, therefore, is where does this problem lie? Is it a bug in
Metalog that it doesn't properly parse the message, or is it a bug in
SysLogHandler that it doesn't properly format it? I guess it could
also be that if one wants to use the SysLogHandler, then that
particular format string must be used to ensure compatibility with all
syslog daemons. I found a couple of examples[2][3] of people
describing the usage of SysLogHandler, but none of them mention a
problem with formatting.

Any thoughts or suggestions would be appreciated. I will patch my
program to use the latter format string for now, but I  would still
like to find the root cause for this problem.

Regards,
Dustin C. Hatch

[1] http://metalog.sourceforge.net/
[2] 
http://scottbarnham.com/blog/2008/01/01/sysloghandler-not-writing-to-syslog-with-python-logging/
[3] 
http://www.mechanicalcat.net/richard/log/Python/Simple_usage_of_Python_s_logging_module
-- 
http://mail.python.org/mailman/listinfo/python-list

hashkey/digest for a complex object

2010-10-06 Thread kj



The short version of this question is: where can I find the algorithm
used by the tuple class's __hash__ method?

Now, for the long version of this question, I'm working with some
complext Python objects that I want to be able to compare for
equality easily.

These objects are non-mutable once they are created, so I would
like to use a two-step comparison for equality, based on the
assumption that I can compute (either at creation time, or as needed
and memoized) a hashkey/digest for each object.  The test for
equality of two of these objects would first compare their hashkeys.
If they are different, the two objects are declared different; if
they match, then a more stringent test for equality is performed.

So the problem is to come up with a reasonable hashkey for each of
these objects.  The objects have two significant attributes, and
two of these objects should be regarded as equal if these attributes
are the same in both.  The first attribute is a simple dictionary
whose keys are integers and values are strings.  The second attribute
is more complicated.  It is a tree structure, represented as a
dictionary of dictionaries of dictionaries... until we get to the
leaf elements, which are frozensets of strings.  The keys at every
level of this structure are strings.  E.g. a simple example of such
an attribute would look like:

{'A': {'a': set(['1', '2', '3']),
   'b': set(['4', '5'])},
 'B': set(['6', '7', '8'])}

I'm looking for a good algorithm for computing a hash key for
something like this?  (Basically I'm looking for a good way to
combine hashkeys.)

Thanks!

kj










-- 
http://mail.python.org/mailman/listinfo/python-list

Re: C++ vs. Python Was: Re: help!!!

2010-10-06 Thread Krister Svanlund

On Wed, Oct 6, 2010 at 12:16 PM, Hans-Peter Jansen h...@urpla.net wrote:
 On Wednesday 06 October 2010, 06:28:51 Dennis Lee Bieber wrote:
 On Tue, 05 Oct 2010 23:54:00 -0400, fkr...@aboutrafi.net23.net

 declaimed the following in gmane.comp.python.general:
  plz can u convert this cpp file into python i need that badly as soon
  as possible... I am new to python. I just wanna learn it

       Step one... DON'T TRY TO PORT C++ to Python... the object models are
 quite different.

 I do this all the time without any adverse effects (other than being glad to
 only rarely having the need of doing it the other way around ;-)).

I have on occasion translated a few algorithms from python to c++ and
only needed to spend minimal time pythonize the code. Generally I
believe that porting from python to c++ and the other way around can
be done pretty nicely but you always have to take care to restructure
what has to be restructured.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: suggestions please what should i watch for/guard against' in a file upload situation?

2010-10-06 Thread Tim Chase


On 10/06/10 12:14, Seebs wrote:

not sure what else i could do to guard against anything bad
happening.  maybe the file name itself could cause greif?


Obvious things:

* File name causes files to get created outside some particular
   upload directory (../foo)
* File name has spaces
* Crazy stuff like null bytes in file name
* File names which might break things if a user carelessly interacts
   with them, such as foo.jpg /etc/passwd bar.jpg (all one file name
   including two spaces).


And depending on the system, Win32 chokes on filenames like 
nul, con, com1...comN, lpt1...lptN, and a bunch of 
others.


-tkc




--
http://mail.python.org/mailman/listinfo/python-list

python-2.6.6 coredump running newspipe

2010-10-06 Thread Thomas Klausner

Hi!

I'm running newspipe-1.1.9, an RSS reader
(http://newspipe.sourceforge.net/), on NetBSD-5.99.11/amd64 using
Python-2.6.6.

Sometimes, it core dumps with particular feeds in the configuration (I
guess depending on the feed, because when I comment out the offending
feed in the opml file, it runs through to completion).

The backtrace looks like this:
Core was generated by `python'.
Program terminated with signal 10, Bus error.
#0  0x7f7ffdc35a21 in PyOS_snprintf (str=0x7f7ff5dfe3d8 @, size=120, 
format=0x1 Address 0x1 out of bounds) at Python/mysnprintf.c:43
43  {
(gdb) bt
#0  0x7f7ffdc35a21 in PyOS_snprintf (str=0x7f7ff5dfe3d8 @, size=120, 
format=0x1 Address 0x1 out of bounds) at Python/mysnprintf.c:43
#1  0x7f7ffdc471a6 in PyOS_ascii_formatd (buffer=0x7f7ff5dfe3d8 @, 
buf_size=120, format=0x7f7ff5dfe388 %.2f, d=0.15256118774414062) at 
Python/pystrtod.c:455
#2  0x7f7ffdbaa7fa in formatfloat (buf=0x7f7ff5dfe3d8 @, buflen=120, 
flags=16, prec=2, type=102, v=0x7f7ffcc6d510) at Objects/stringobject.c:4378
#3  0x7f7ffdbabd32 in PyString_Format (format=0x7f7ffc8144e0, 
args=0x7f7ffcc6d510) at Objects/stringobject.c:4943
#4  0x7f7ffdbaa3b0 in string_mod (v=0x7f7ffc8144e0, w=0x7f7ffcc6d510) at 
Objects/stringobject.c:4116
#5  0x7f7ffdb459db in binary_op1 (v=0x7f7ffc8144e0, w=0x7f7ffcc6d510, 
op_slot=32) at Objects/abstract.c:917
#6  0x7f7ffdb45c81 in binary_op (v=0x7f7ffc8144e0, w=0x7f7ffcc6d510, 
op_slot=32, op_name=0x7f7ffdc6c089 %) at Objects/abstract.c:969
#7  0x7f7ffdb467ad in PyNumber_Remainder (v=0x7f7ffc8144e0, 
w=0x7f7ffcc6d510) at Objects/abstract.c:1221
#8  0x7f7ffdc08a03 in PyEval_EvalFrameEx (f=0x7f7fefa1dab0, throwflag=0) at 
Python/ceval.c:1180
#9  0x7f7ffdc1175f in fast_function (func=0x7f7ff8a9bed8, 
pp_stack=0x7f7ff5dfeae8, n=1, na=1, nk=0) at Python/ceval.c:3836
#10 0x7f7ffdc11565 in call_function (pp_stack=0x7f7ff5dfeae8, oparg=1) at 
Python/ceval.c:3771
#11 0x7f7ffdc0d81f in PyEval_EvalFrameEx (f=0x7f7fee920420, throwflag=0) at 
Python/ceval.c:2412
#12 0x7f7ffdc0f715 in PyEval_EvalCodeEx (co=0x7f7ffcc247b0, 
globals=0x7f7ffd1c5880, locals=0x0, args=0x7f7ff5b0aac8, argcount=8, 
kws=0x7f7ff5b0ab08, kwcount=0, defs=0x7f7ff8d3c4e8,
defcount=5, closure=0x0) at Python/ceval.c:3000
#13 0x7f7ffdc1184a in fast_function (func=0x7f7ff8a9cc80, 
pp_stack=0x7f7ff5dfeff8, n=8, na=8, nk=0) at Python/ceval.c:3846
#14 0x7f7ffdc11565 in call_function (pp_stack=0x7f7ff5dfeff8, oparg=7) at 
Python/ceval.c:3771
#15 0x7f7ffdc0d81f in PyEval_EvalFrameEx (f=0x7f7ff5b0a820, throwflag=0) at 
Python/ceval.c:2412
#16 0x7f7ffdc1175f in fast_function (func=0x7f7ff8a9e140, 
pp_stack=0x7f7ff5dff358, n=1, na=1, nk=0) at Python/ceval.c:3836
#17 0x7f7ffdc11565 in call_function (pp_stack=0x7f7ff5dff358, oparg=0) at 
Python/ceval.c:3771
#18 0x7f7ffdc0d81f in PyEval_EvalFrameEx (f=0x7f7ff5b0a420, throwflag=0) at 
Python/ceval.c:2412
#19 0x7f7ffdc1175f in fast_function (func=0x7f7ffca1db90, 
pp_stack=0x7f7ff5dff6b8, n=1, na=1, nk=0) at Python/ceval.c:3836
#20 0x7f7ffdc11565 in call_function (pp_stack=0x7f7ff5dff6b8, oparg=0) at 
Python/ceval.c:3771
#21 0x7f7ffdc0d81f in PyEval_EvalFrameEx (f=0x7f7ff5b03190, throwflag=0) at 
Python/ceval.c:2412
#22 0x7f7ffdc0f715 in PyEval_EvalCodeEx (co=0x7f7ffca0d4e0, 
globals=0x7f7ffca473a0, locals=0x0, args=0x7f7ff04d3e68, argcount=1, kws=0x0, 
kwcount=0, defs=0x0, defcount=0, closure=0x0)
at Python/ceval.c:3000
#23 0x7f7ffdb7a612 in function_call (func=0x7f7ffca1daa0, 
arg=0x7f7ff04d3e50, kw=0x0) at Objects/funcobject.c:524
#24 0x7f7ffdb495e8 in PyObject_Call (func=0x7f7ffca1daa0, 
arg=0x7f7ff04d3e50, kw=0x0) at Objects/abstract.c:2492
#25 0x7f7ffdb5eca0 in instancemethod_call (func=0x7f7ffca1daa0, 
arg=0x7f7ff04d3e50, kw=0x0) at Objects/classobject.c:2579
#26 0x7f7ffdb495e8 in PyObject_Call (func=0x7f7ff8ac2a00, 
arg=0x7f7ffd112050, kw=0x0) at Objects/abstract.c:2492
#27 0x7f7ffdc10cd3 in PyEval_CallObjectWithKeywords (func=0x7f7ff8ac2a00, 
arg=0x7f7ffd112050, kw=0x0) at Python/ceval.c:3619
#28 0x7f7ffdc4e69f in t_bootstrap (boot_raw=0x7f7ffd1b4590) at 
./Modules/threadmodule.c:428
#29 0x7f7ffd90ba32 in pthread_setcancelstate () from 
/usr/lib/libpthread.so.1
#30 0x7f7ffd26e9b0 in ___lwp_park50 () from /usr/lib/libc.so.12
#31 0x in ?? ()
(gdb) fr 1
#1  0x7f7ffdc471a6 in PyOS_ascii_formatd (buffer=0x7f7ff5dfe3d8 @, 
buf_size=120, format=0x7f7ff5dfe388 %.2f, d=0.15256118774414062) at 
Python/pystrtod.c:455
455 PyOS_snprintf(buffer, buf_size, format, d);
(gdb) l
450 format = tmp_format;
451 }
452
453
454 /* Have PyOS_snprintf do the hard work */
455 PyOS_snprintf(buffer, buf_size, format, d);
456
457 /* Do various fixups on the return string */
458
459 /* Get the current locale, and find the decimal point string.
(gdb) p format
$1 = 0x7f7ff5dfe388 %.2f
(gdb) fr 0
#0

Re: help!!!

fkr...@aboutrafi.net23.net writes:

 plz can u convert this cpp file into python i need that badly as soon as 
 possible... I am new to python. I just wanna learn it

For such an aspiring student of the art of computer programming, I have
the strange feeling of lack-of-effort-showing here. Do I have to lose my
faith in youth?

Diez
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Re: How to save a binary file?

Ppl thanyou, for all your help finally i did it! thanks, another thing  
to i have to send a propouse code, i can fixed the litle problem of the  
wsig.input in Python 3 i will tested in the next months but i want to share  
the code with the comunnity, how i can do that?


On Oct 6, 2010 1:45pm, MRAB pyt...@mrabarnett.plus.com wrote:

On 06/10/2010 15:25, hid...@gmail.com wrote:




When you put the 'wb' extension you have to pass a Encode the string



Python does not accept a string on a wb file, Python3






[snip]



You are using Python 3 and type(str) returns ?





Binary data in Python 3 should be an instance of the 'bytes' class, not



an instance of the 'str' class.





If you can't fix that, you could turn the string into bytes using:





data = bytes(ord(c) for c in str)





or by carefully choosing an encoding which would give the same result:





data = str.encode('latin-1')





Then you can save it:





s = open('/home/hidura/test.jpeg', 'wb')



s.write(data)



s.close()





I asked you to look at the result of repr so that you could see more



clearly what the data actually looked like, an instance of str or an



instance of bytes.



--



http://mail.python.org/mailman/listinfo/python-list


-- 
http://mail.python.org/mailman/listinfo/python-list

Re: hashkey/digest for a complex object

2010-10-06 Thread Duncan Booth

kj no.em...@please.post wrote:

 The short version of this question is: where can I find the algorithm
 used by the tuple class's __hash__ method?
 

http://svn.python.org/view/python/trunk/Objects/tupleobject.c?revision=81029view=markup

static long
tuplehash(PyTupleObject *v)
{
register long x, y;
register Py_ssize_t len = Py_SIZE(v);
register PyObject **p;
long mult = 103L;
x = 0x345678L;
p = v-ob_item;
while (--len = 0) {
y = PyObject_Hash(*p++);
if (y == -1)
return -1;
x = (x ^ y) * mult;
/* the cast might truncate len; that doesn't change hash stability */
mult += (long)(82520L + len + len);
}
x += 97531L;
if (x == -1)
x = -2;
return x;
}



 I'm looking for a good algorithm for computing a hash key for
 something like this?  (Basically I'm looking for a good way to
 combine hashkeys.)

If you want to combine the hashes from several objects then the 
easiest way is just to create a tuple of the objects and hash it.

-- 
Duncan Booth http://kupuguy.blogspot.com
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Re: Re: How to save a binary file?

Ppl thanyou, for all your help finally i did it! thanks, another thing  
to who i can send a propose code, i fixed the little problem of the  
wsig.input in Python 3 i will tested in the next months but i want to share  
the code with the community, how i can do that?


On Oct 6, 2010 3:13pm, hid...@gmail.com wrote:
Ppl thanyou, for all your help finally i did it! thanks, another  
thing to i have to send a propouse code, i can fixed the litle problem of  
the wsig.input in Python 3 i will tested in the next months but i want to  
share the code with the comunnity, how i can do that?



On Oct 6, 2010 1:45pm, MRAB pyt...@mrabarnett.plus.com wrote:
 On 06/10/2010 15:25, hid...@gmail.com wrote:


 When you put the 'wb' extension you have to pass a Encode the string

 Python does not accept a string on a wb file, Python3




 [snip]

 You are using Python 3 and type(str) returns ?



 Binary data in Python 3 should be an instance of the 'bytes' class, not

 an instance of the 'str' class.



 If you can't fix that, you could turn the string into bytes using:



 data = bytes(ord(c) for c in str)



 or by carefully choosing an encoding which would give the same result:



 data = str.encode('latin-1')



 Then you can save it:



 s = open('/home/hidura/test.jpeg', 'wb')

 s.write(data)

 s.close()



 I asked you to look at the result of repr so that you could see more

 clearly what the data actually looked like, an instance of str or an

 instance of bytes.

 --

 http://mail.python.org/mailman/listinfo/python-list

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: suggestions please what should i watch for/guard against' in a file upload situation?

Seebs usenet-nos...@seebs.net writes:

 On 2010-10-06, geekbuntu gmi...@gmail.com wrote:
 in general, what are things i would want to 'watch for/guard against'
 in a file upload situation?

 This question has virtually nothing to do with Python, which means you
 may not get very good answers.

In contrast to comp.super.web.experts? There are quite a few people
with web-experience here I'd say. 


 my checklist so far is basically to check the extension - ensure it
 has 3 places, ensure it's in the allowed list (like jpg gif etc...).

 This strikes me as 100% irrelevant.  Who cares what the extension is?

Given that most people are not computer savvy (always remember, the
default for windows is to hide extensions..), using it client-side can
be valuable to prevent long uploads that eventuall need to be rejected
otherwise (no mom, you can't upload word-docs as profile pictures).

 not sure what else i could do to guard against anything bad
 happening.  maybe the file name itself could cause greif?

 Obvious things:

 * File name causes files to get created outside some particular
   upload directory (../foo)

Or rather just store that as a simple meta-info, as allowing even the
best-intended me-in-cool-pose.jpg to overwrite that of the one other
cool guy using the website isn't gonna fly anyway.

 * File name has spaces

See above, but other then that - everything but shell-scripts deal well
with it.

 * Crazy stuff like null bytes in file name
 * File names which might break things if a user carelessly interacts
   with them, such as foo.jpg /etc/passwd bar.jpg (all one file name
   including two spaces).

Your strange focus on file-names that are pure meta information is a
little bit concerning... 

 Basically, the key question is, could a hostile user come up with
 input to your script which could break something?

Certainly advice. But that's less focussed on filenames or file-uploads, but
on the whole subject of processing HTTP-requestst. Which would make a
point for *not* using a home-grown framework.

But then, Python is a bit less likely to suffer from buffer overflow or 
similar kind of attacks.

Diez
-- 
http://mail.python.org/mailman/listinfo/python-list

list parameter of a recursive function

Hi,

I have a function f that calls itself recursively. It has a list as second 
argument, with default argument equal to None (and not [], as indicated at:
http://www.ferg.org/projects/python_gotchas.html#contents_item_6 )

This is the outline of my function:

def f ( argument, some_list = None ):

   if some_list == None:
  some_list = []
   [...]
   # creation of a new_argument
   # the function is called recursively only if some condition is respected
   if some_condition:
  some_list.append( elem )
  f( new_argument, some_list )
   # otherwise, we have reached a leaf of the a branch of the recursive tree
   # (said differently, terminal condition has been reached for this branch)
   print Terminal condition

The problem is that when the terminal condition is reached, we return back 
to some other branch of the recursive tree, but some_list has the value 
obtained in the previous branch!
So, it seems that there is only one some_list list for all the recursive 
tree.
To get rid of this behavior, I have been compelled to do at the beginning of 
f:

import copy from copy
some_list = copy( some_list )

I suppose this is not a surprise to you: I am compelled to create a new 
some_list with the same content.
So, if I am right, all is happening as if the parameters of a function are 
always passed by address to the function. Whereas in C, they are always 
passed by copy (which gives relevance to pointers).

Am I right?

Julien

-- 
python -c print ''.join([chr(154 - ord(c)) for c in '*9(9(18%.\
91+,\'Z4(55l4('])

When a distinguished but elderly scientist states that something is
possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong. (first law of AC Clarke)
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: hashkey/digest for a complex object

2010-10-06 Thread geremy condra

On Wed, Oct 6, 2010 at 11:58 AM, kj no.em...@please.post wrote:


 The short version of this question is: where can I find the algorithm
 used by the tuple class's __hash__ method?

From Objects/tuple.c, line 315 in Python3.2:

static long
tuplehash(PyTupleObject *v)
{
register long x, y;
register Py_ssize_t len = Py_SIZE(v);
register PyObject **p;
long mult = 103L;
x = 0x345678L;
p = v-ob_item;
while (--len = 0) {
y = PyObject_Hash(*p++);
if (y == -1)
return -1;
x = (x ^ y) * mult;
/* the cast might truncate len; that doesn't change hash stability */
mult += (long)(82520L + len + len);
}
x += 97531L;
if (x == -1)
x = -2;
return x;
}

 Now, for the long version of this question, I'm working with some
 complext Python objects that I want to be able to compare for
 equality easily.

 These objects are non-mutable once they are created, so I would
 like to use a two-step comparison for equality, based on the
 assumption that I can compute (either at creation time, or as needed
 and memoized) a hashkey/digest for each object.  The test for
 equality of two of these objects would first compare their hashkeys.
 If they are different, the two objects are declared different; if
 they match, then a more stringent test for equality is performed.

 So the problem is to come up with a reasonable hashkey for each of
 these objects.  The objects have two significant attributes, and
 two of these objects should be regarded as equal if these attributes
 are the same in both.  The first attribute is a simple dictionary
 whose keys are integers and values are strings.  The second attribute
 is more complicated.  It is a tree structure, represented as a
 dictionary of dictionaries of dictionaries... until we get to the
 leaf elements, which are frozensets of strings.  The keys at every
 level of this structure are strings.  E.g. a simple example of such
 an attribute would look like:

 {'A': {'a': set(['1', '2', '3']),
       'b': set(['4', '5'])},
  'B': set(['6', '7', '8'])}

 I'm looking for a good algorithm for computing a hash key for
 something like this?  (Basically I'm looking for a good way to
 combine hashkeys.)

Sounds like you're trying to hash mutable data structures, which is a
no-no, but assuming you've got that part all figured out then the easy
way out would be to print the whole thing and take the hash of the
resulting string. A (possibly) better way would be to do a Schwartzian
transform[1] and freeze everything. Other approaches may be better,
but those are the first two out of my head.

Geremy Condra

[1] http://en.wikipedia.org/wiki/Schwartzian_transform
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: hashkey/digest for a complex object

kj no.em...@please.post writes:

The short version of this question is: where can I find the algorithm
used by the tuple class's __hash__ method?

Surprisingly, in the source:

http://google.com/codesearch/p?hl=de#-2BKs-LW4I0/trunk/python/src/Objects/tupleobject.cq=python%20tuplehashsa=Ncd=1ct=rc

Now, for the long version of this question, I'm working with some
complext Python objects that I want to be able to compare for
equality easily.

These objects are non-mutable once they are created, so I would
like to use a two-step comparison for equality, based on the
assumption that I can compute (either at creation time, or as needed
and memoized) a hashkey/digest for each object. The test for
equality of two of these objects would first compare their hashkeys.
If they are different, the two objects are declared different; if
they match, then a more stringent test for equality is performed.

So the problem is to come up with a reasonable hashkey for each of
these objects. The objects have two significant attributes, and
two of these objects should be regarded as equal if these attributes
are the same in both. The first attribute is a simple dictionary
whose keys are integers and values are strings. The second attribute
is more complicated. It is a tree structure, represented as a
dictionary of dictionaries of dictionaries... until we get to the
leaf elements, which are frozensets of strings. The keys at every
level of this structure are strings. E.g. a simple example of such
an attribute would look like:

{'A': {'a': set(['1', '2', '3']),
'b': set(['4', '5'])},
'B': set(['6', '7', '8'])}

I'm looking for a good algorithm for computing a hash key for
something like this? (Basically I'm looking for a good way to
combine hashkeys.)

Creating tuples from dicts, recursively, and stabilized by using sorted
on items.

Diez
--
http://mail.python.org/mailman/listinfo/python-list

Re: hashkey/digest for a complex object

2010-10-06 Thread Robert Kern


On 10/6/10 1:58 PM, kj wrote:


The short version of this question is: where can I find the algorithm
used by the tuple class's __hash__ method?


The function tuplehash() in Objects/tupleobject.c, predictably enough.


Now, for the long version of this question, I'm working with some
complext Python objects that I want to be able to compare for
equality easily.

These objects are non-mutable once they are created, so I would
like to use a two-step comparison for equality, based on the
assumption that I can compute (either at creation time, or as needed
and memoized) a hashkey/digest for each object.  The test for
equality of two of these objects would first compare their hashkeys.
If they are different, the two objects are declared different; if
they match, then a more stringent test for equality is performed.


The most straightforward way to implement __hash__ for a complicated object is 
to normalize its relevant data to a tuple of hashable objects and then call 
hash() on that tuple. A straightforward way to compare such objects is to 
calculate that very same normalized tuple for each one and compare those tuples. 
Cache it if necessary. Don't bother hashing to implement __eq__ unless if you 
are really optimizing for space and time.


--
Robert Kern

I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth.
  -- Umberto Eco

--
http://mail.python.org/mailman/listinfo/python-list

Re: suggestions please what should i watch for/guard against' in a file upload situation?

2010-10-06 Thread Martin Gregorie

On Wed, 06 Oct 2010 09:02:21 -0700, geekbuntu wrote:

 in general, what are things i would want to 'watch for/guard against' in
 a file upload situation?
 
 i have my file upload working (in the self-made framework @ work without
 any concession for multipart form uploads), but was told to make sure
 it's cleansed and cannot do any harm inside the system.

Off the top of my head, and assuming that you get passed the exact 
filename that the user entered:

- The user may need to use an absolute pathname to upload a file
  that isn't in his current directory, so retain only the basename
  by discarding the rightmost slash and everything to the left of it:
/home/auser/photos/my_photo.jpg   === my_photo.jpg
c:\My Photos\My Photo.jpg === My Photo.jpg

- If your target system doesn't like spaces in names or you want to be
  on the safe side there, replace spaces in the name with underscores:
My Photo.jpg ===My_Photo.jpg

- reject any filenames that could cause the receiving system to do
  dangerous things, e.g. .EXE or .SCR if the upload target is Windows.
  This list will be different for each upload target, so make it 
  configurable.

  You can't assume anything about else about the extension. 
  .py .c .txt and .html are all valid in the operating systems I use
  and so are their capitalised equivalents. 

- check whether the file already exists. You need
  rules about what to do if it exists (do you reject the upload,
  silently overwrite, or alter the name, e.g. by adding a numeric
  suffix to make the name unique:

 my_photo.jpg  ===  my_photo-01.jpg

- run the application in your upload target directory and put the
  uploaded file there or, better, into a configured uploads directory
  by prepending it to the file name:

my_photo.jpg   ===  /home/upload_user/uploads/my_photo.jpg

- make sure you document the process so that a user can work out
  what has happened to his file and why if you have to reject it
  or alter its name.

 not sure but any suggestions or examples are most welcome :)

There's probably something I've forgotten, but that list should get you 
going.
 


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org   |
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: list parameter of a recursive function

2010-10-06 Thread Chris Torek

In article rsuun7-eml@rama.universe
TP  tribulati...@paralleles.invalid wrote:
I have a function f that calls itself recursively. It has a list as second 
argument, with default argument equal to None (and not [], as indicated at:
http://www.ferg.org/projects/python_gotchas.html#contents_item_6 )

This is the outline of my function:

def f ( argument, some_list = None ):

   if some_list == None:
  some_list = []
   [...]
   # creation of a new_argument
   # the function is called recursively only if some condition is respected
   if some_condition:
  some_list.append( elem )
  f( new_argument, some_list )
   # otherwise, we have reached a leaf of the a branch of the recursive tree
   # (said differently, terminal condition has been reached for this branch)
   print Terminal condition

The problem is that when the terminal condition is reached, we return back 
to some other branch of the recursive tree, but some_list has the value 
obtained in the previous branch!

Yes, this is the way it is supposed to work. :-)

So, it seems that there is only one some_list list for all the recursive 
tree.  To get rid of this behavior, I have been compelled to do at the
beginning of f:

import copy from copy

[from copy import copy, rather]

some_list = copy( some_list )

I suppose this is not a surprise to you: I am compelled to create a new 
some_list with the same content.

The above will work, or for this specific case, you can write:

some_list = list(some_list)

which has the effect of making a shallow copy of an existing list:

base = [1, 2]
l1 = base
l2 = list(l1)
l1 is l2
   False
l1[0] is l2[0]
   True
base.append(3)
l2
   [[1, 2, 3]]
   

but will also turn *any* iterator into a (new) list; the latter
may often be desirable.

So, if I am right, all is happening as if the parameters of a function are 
always passed by address to the function. Whereas in C, they are always 
passed by copy (which gives relevance to pointers).

Am I right?

Mostly.  Python distinguishes between mutable and immutable items.
Mutable items are always mutable, immutable items are never mutable,
and the mutability of arguments is attached to their fundamental
mutability rather than to their being passed as arguments.  This
is largely a point-of-view issue (although it matters a lot to
people writing compilers, for instance).

Note that if f() is *supposed* to be able to modify its second
parameter under some conditions, you would want to make the copy
not at the top of f() but rather further in, and in this case,
that would be trivial:

def f(arg, some_list = None):
if some_list is None:
some_list = []
...
if some_condition:
# make copy of list and append something
f(new_arg, some_list + [elem])
elif other_condition:
# continue modifying same list
f(new_arg, some_list)
...

(Note: you can use also the fact that list1 + list2 produces a new
list to make a copy by writing x = x + [], or x = [] + x, but
x = list(x) is generally a better idea here.)
-- 
In-Real-Life: Chris Torek, Wind River Systems
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W)  +1 801 277 2603
email: gmail (figure it out)  http://web.torek.net/torek/index.html
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Strong typing vs. strong testing

2010-10-06 Thread RG

In article 
1a172248-8aab-42f0-a8a2-3f00168f9...@u13g2000vbo.googlegroups.com,
 Keith H Duggar dug...@alum.mit.edu wrote:

 On Sep 29, 9:01 pm, RG rnospa...@flownet.com wrote:
  That the problem is elsewhere in the program ought to be small
  comfort.  But very well, try this instead:
 
  [...@mighty:~]$ cat foo.c
  #include stdio.h
 
  int maximum(int a, int b) { return a  b ? a : b; }
 
  int main() {
    long x = 8589934592;
    printf(Max of %ld and 1 is %d\n, x, maximum(x,1));
    return 0;}
 
  [...@mighty:~]$ gcc -Wall foo.c
  [...@mighty:~]$ ./a.out
  Max of 8589934592 and 1 is 1
 
 $ gcc -Wconversion -Werror foo.c
 cc1: warnings being treated as errors
 foo.c: In function 'main':
 foo.c:5: warning: passing argument 1 of 'maximum' with different width
 due to prototype
 
 It's called learning to compile.

It's called being late for the game.  This has already been raised and 
addressed.  Read the rest of the thread.

rg
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: list parameter of a recursive function

Chris Torek wrote:

import copy from copy
 
 [from copy import copy, rather]

Yes, sorry.

 Note that if f() is *supposed* to be able to modify its second
 parameter under some conditions, you would want to make the copy
 not at the top of f() but rather further in, and in this case,
 that would be trivial:
 
 def f(arg, some_list = None):
 if some_list is None:
 some_list = []
 ...
 if some_condition:
 # make copy of list and append something
 f(new_arg, some_list + [elem])
 elif other_condition:
 # continue modifying same list
 f(new_arg, some_list)

Thanks a lot Chris!
I think I prefer doing an explicit copy.copy, because it allows to remind 
the reader that it is very important to take care of that. But your trick is 
very interesting also.

Cheers,

Julien


-- 
python -c print ''.join([chr(154 - ord(c)) for c in '*9(9(18%.\
91+,\'Z4(55l4('])

When a distinguished but elderly scientist states that something is
possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong. (first law of AC Clarke)
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

On 2010-10-06, Diez B. Roggisch de...@web.de wrote:
fkr...@aboutrafi.net23.net writes:
 plz can u convert this cpp file into python i need that badly as soon as 
 possible... I am new to python. I just wanna learn it

 For such an aspiring student of the art of computer programming, I have
 the strange feeling of lack-of-effort-showing here. Do I have to lose my
 faith in youth?

Never!

Just be sure you are having faith in them to, well, be youth.  :)

-s
-- 
Copyright 2010, all wrongs reversed.  Peter Seebach / usenet-nos...@seebs.net
http://www.seebs.net/log/ -- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) -- get educated!
I am not speaking for my employer, although they do rent some of my opinions.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: suggestions please what should i watch for/guard against' in a file upload situation?

On 2010-10-06, Diez B. Roggisch de...@web.de wrote:
 Seebs usenet-nos...@seebs.net writes:
 On 2010-10-06, geekbuntu gmi...@gmail.com wrote:
 in general, what are things i would want to 'watch for/guard against'
 in a file upload situation?

 This question has virtually nothing to do with Python, which means you
 may not get very good answers.

 In contrast to comp.super.web.experts? There are quite a few people
 with web-experience here I'd say. 

Oh, certainly.  But in general, I try to ask questions in a group focused
on their domain, rather than merely a group likely to contain people who
would for other reasons have the relevant experience.  I'm sure that a great
number of Python programmers have experience with sex, that doesn't make
this a great newsgroup for sex tips.  (Well, maybe it does.)

 Given that most people are not computer savvy (always remember, the
 default for windows is to hide extensions..), using it client-side can
 be valuable to prevent long uploads that eventuall need to be rejected
 otherwise (no mom, you can't upload word-docs as profile pictures).

That's a good point.  On the other hand, there's a corollary; you may want
to look at the contents of the file in case they're not really what they're
supposed to be.

 Your strange focus on file-names that are pure meta information is a
 little bit concerning... 

If you're uploading files into a directory, then it is quite likely that
you're getting file names from somewhere.  Untrusted file names are a much
more effective attack vector, in most cases, than EXIF information.

 Certainly advice. But that's less focussed on filenames or file-uploads, but
 on the whole subject of processing HTTP-requestst. Which would make a
 point for *not* using a home-grown framework.

Well, yeah.  I was assuming that the home-grown framework was mandatory for
some reason.  Possibly a very important reason, such as otherwise we won't
have written it ourselves.

-s
-- 
Copyright 2010, all wrongs reversed.  Peter Seebach / usenet-nos...@seebs.net
http://www.seebs.net/log/ -- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) -- get educated!
I am not speaking for my employer, although they do rent some of my opinions.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

On Tue, 05 Oct 2010 23:54:00 -0400, fkrafi wrote:

 plz can u convert this cpp file into python i need that badly as soon as
 possible... I am new to python. I just wanna learn it

Good grief. It's bad enough to expect us to do your coding for you, 
without making even the *tiniest* effort to learn yourself, but then to 
add insult to injury you use text-speak.

ur nt sending sms now, learn to rite the wrds

If you want to learn Python, I suggest you work through some tutorials. 
Google is your friend: google on python tutorial and see what comes up.



-- 
Steven
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: list parameter of a recursive function

TP tribulati...@paralleles.invalid writes:

 Hi,

 I have a function f that calls itself recursively. It has a list as second 
 argument, with default argument equal to None (and not [], as indicated at:
 http://www.ferg.org/projects/python_gotchas.html#contents_item_6 )

 This is the outline of my function:

 def f ( argument, some_list = None ):

if some_list == None:
   some_list = []
[...]
# creation of a new_argument
# the function is called recursively only if some condition is respected
if some_condition:
   some_list.append( elem )
   f( new_argument, some_list )
# otherwise, we have reached a leaf of the a branch of the recursive tree
# (said differently, terminal condition has been reached for this branch)
print Terminal condition

 The problem is that when the terminal condition is reached, we return back 
 to some other branch of the recursive tree, but some_list has the value 
 obtained in the previous branch!
 So, it seems that there is only one some_list list for all the recursive 
 tree.
 To get rid of this behavior, I have been compelled to do at the beginning of 
 f:

 import copy from copy
 some_list = copy( some_list )

 I suppose this is not a surprise to you: I am compelled to create a new 
 some_list with the same content.
 So, if I am right, all is happening as if the parameters of a function are 
 always passed by address to the function. Whereas in C, they are always 
 passed by copy (which gives relevance to pointers).

 Am I right?

Yes and no. For some sensible definition of yes (this is to avoid the
*endless* discussions about python parameter passing semantics and it's
relation to common, yet misunderstood or unprecisely defined definitions
of parameter passing), passing around a mutable object (such as a list
or dictionary) will be like a pointer - mutations are visible to all
others having a reference to it.

You are wrong though that C-semantics are different, meaning that
passing by copy is not what happens. Some things are copied (primitive
types, structs that are passed directly). But not, for example - and
relevant to this case - arrays (as they are only pointers), lists (as they
don't exist, but are modeled by structs containing pointers).

Back to your example: your solution is perfectly fine, although a bit
costly and more error-prone if you happen to forget to create a copy.
A safer alternative for these cases is using tuples, because they are
immutable. 

Diez
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: suggestions please what should i watch for/guard against' in a file upload situation?

On Wed, 06 Oct 2010 09:02:21 -0700, geekbuntu wrote:

 in general, what are things i would want to 'watch for/guard against' in
 a file upload situation?
 
 i have my file upload working (in the self-made framework @ work without
 any concession for multipart form uploads), but was told to make sure
 it's cleansed and cannot do any harm inside the system.

Make sure *what* is cleansed? Your code? The uploaded files? Define 
cleansed.

Do you have to block viruses, malware, spybots, illegal pornography, 
legal pornography, illegal content, warez, copyright violations, stolen 
trade secrets, dirty words, pictures of cats?

What operating system are you uploading to?

What happens if somebody tries to upload a 1 TB file to your server?

What happens if they try to upload a billion 1 KB files instead?


 
 my checklist so far is basically to check the extension - ensure it has
 3 places, ensure it's in the allowed list (like jpg gif etc...).

Do you have something against file extensions like .gz or .jpeg ?

I'm not sure why you think you need to check the file extension.

 
 not sure what else i could do to guard against anything bad happening. 
 maybe the file name itself could cause greif?

You think? :)

What happens if the file name has characters in it that your file system 
can't deal with? Bad unicode, binary bytes, slashes, colons, question 
marks, asterisks, etc.

What about trying to break out of your file storage area using .. paths?

Without knowing what your file upload code actually does, it's hard to 
give specific advice.


-- 
Steven
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: list parameter of a recursive function

On Wed, 06 Oct 2010 23:00:10 +0200, TP wrote:

 I think I prefer doing an explicit copy.copy, because it allows to
 remind the reader that it is very important to take care of that. 

I think a comment is better for that. It's better to explicitly say 
something is important than to assume the reader will guess.

Besides, what if the caller wants to supply their own list, and they 
*want* it modified in place rather than a copy made? (I have no idea why 
they might want this, but anything is possible...) You should avoid 
making copies except in methods that are *for* making copies.


-- 
Steven
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: suggestions please what should i watch for/guard against' in a file upload situation?

Seebs usenet-nos...@seebs.net writes:

 On 2010-10-06, Diez B. Roggisch de...@web.de wrote:
 Seebs usenet-nos...@seebs.net writes:
 On 2010-10-06, geekbuntu gmi...@gmail.com wrote:
 in general, what are things i would want to 'watch for/guard against'
 in a file upload situation?

 This question has virtually nothing to do with Python, which means you
 may not get very good answers.

 In contrast to comp.super.web.experts? There are quite a few people
 with web-experience here I'd say. 

 Oh, certainly.  But in general, I try to ask questions in a group focused
 on their domain, rather than merely a group likely to contain people who
 would for other reasons have the relevant experience.  I'm sure that a great
 number of Python programmers have experience with sex, that doesn't make
 this a great newsgroup for sex tips.  (Well, maybe it does.)

As the OP asked about a Python web framework (self written or not), I
think all advice that can be given is certainly more related to Python
than to airy references to general web programming such as 
oh, make sure if your server side application environment hasn't any 
security issues.

Or, to be more concrete: what NG would you suggest for frameworks or webapps
written in python to ask this question?

 Given that most people are not computer savvy (always remember, the
 default for windows is to hide extensions..), using it client-side can
 be valuable to prevent long uploads that eventuall need to be rejected
 otherwise (no mom, you can't upload word-docs as profile pictures).

 That's a good point.  On the other hand, there's a corollary; you may want
 to look at the contents of the file in case they're not really what they're
 supposed to be.

For sure. But the focus of you and others seems to be the file-name,
as if that was anything especially dangerous. Matter of factly, it's a
paramteter to a multipart/form-data encoded request body parameter
definition, and as such has a rather locked-down in terms of
null-bytes and such. So you are pretty safe as long as you

 - use standard library request parsing modules such as cgi. If 
   one instist on reading streams bytewise and using ctypes to poke the
   results into memory, you can of course provoke unimaginable havoc..

 - don't use the filename for anything but meta-info. And ususally, they
   are simply regarded as nice that you've provided us with it, we try
make our best to fill an img alt attribute with the basename. 
   But not more. Worth pointing out to the OP to do that. But this is
   *not* a matter of mapping HTTP-request paths to directories I'd wager
   to say. 

Something that is of much more importance (I should have mentioned
earlier, shame on me) is of course file-size. Denying requests that come
with CONTENT_LENGTH over a specified limit, of course respecting
CONTENT_LENGTH and not reading beyond it, and possibly dealing with
chunked-encodings in similarily safe ways (I have to admit I haven't yet
dealt with  one of those myself on a visceral level - 
but as they are part of the HTTP-spec...) is important, 
as otherwise DOS attacks are possible.

 Your strange focus on file-names that are pure meta information is a
 little bit concerning... 

 If you're uploading files into a directory, then it is quite likely that
 you're getting file names from somewhere.  Untrusted file names are a much
 more effective attack vector, in most cases, than EXIF information.

The into a directory quote coming from where? And given that EXIF
information is probably read by some C-lib, I'd say it is much more
dangerous. This is a gut feeling only, but fed by problems with libpng a
year or two ago.

 Certainly advice. But that's less focussed on filenames or file-uploads, but
 on the whole subject of processing HTTP-requestst. Which would make a
 point for *not* using a home-grown framework.

 Well, yeah.  I was assuming that the home-grown framework was mandatory for
 some reason.  Possibly a very important reason, such as otherwise we won't
 have written it ourselves.

In Python, it's usually more along the lines of well, we kinda started,
and now we have it, and are reluctant to switch.

But of course one never knows...

Diez
-- 
http://mail.python.org/mailman/listinfo/python-list

mantissa and exponent in base 10

I want the mantissa and decimal exponent of a float, in base 10:

mantissa and exponent of 1.2345e7 
= (1.2345, 7)

(0.12345, 8) would also be acceptable.


The math module has a frexp() function, but it produces a base-2 exponent:

 math.frexp(1.2345e7)
(0.73581933975219727, 24)

Have I missed a built-in or math function somewhere?



-- 
Steven
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: suggestions please what should i watch for/guard against' in a file upload situation?

Martin Gregorie mar...@address-in-sig.invalid writes:

 On Wed, 06 Oct 2010 09:02:21 -0700, geekbuntu wrote:

 in general, what are things i would want to 'watch for/guard against' in
 a file upload situation?
 
 i have my file upload working (in the self-made framework @ work without
 any concession for multipart form uploads), but was told to make sure
 it's cleansed and cannot do any harm inside the system.

 Off the top of my head, and assuming that you get passed the exact 
 filename that the user entered:

 - The user may need to use an absolute pathname to upload a file
   that isn't in his current directory, so retain only the basename
   by discarding the rightmost slash and everything to the left of it:
 /home/auser/photos/my_photo.jpg   === my_photo.jpg
 c:\My Photos\My Photo.jpg === My Photo.jpg

 - If your target system doesn't like spaces in names or you want to be
   on the safe side there, replace spaces in the name with underscores:
 My Photo.jpg ===My_Photo.jpg

 - reject any filenames that could cause the receiving system to do
   dangerous things, e.g. .EXE or .SCR if the upload target is Windows.
   This list will be different for each upload target, so make it 
   configurable.

Erm, this assumes that the files are executed in some way. Why should
they? It's perfectly fine to upload *anything*, and of course filenames
mean nothing wrt to the actual file contents (Are you sure you want to
change the extension of this file?). 

It might make no sense for the user, because you can't shon an exe as profile
image. But safe-guarding against that has nothing to do with OS. And
even safe file formats such as PNGs have been attack
vectors. Precisely because they are processed client-side in the browser
through some library with security issues.

For serving the files, one could rely on the file-command or similar
means to determine the mime-type. So far, I've never done that - as
faking the extension for something else doesn't buy you something unless
there is a documented case of internet explorer ignoring mime-type, and
executing downloaded file as program.


   You can't assume anything about else about the extension. 
   .py .c .txt and .html are all valid in the operating systems I use
   and so are their capitalised equivalents. 

 - check whether the file already exists. You need
   rules about what to do if it exists (do you reject the upload,
   silently overwrite, or alter the name, e.g. by adding a numeric
   suffix to make the name unique:

  my_photo.jpg  ===  my_photo-01.jpg

Better, associate the file with the uploader and or it's hash. Use the
name as pure meta-information only.

 There's probably something I've forgotten, but that list should get you 
 going.

Dealing with to large upload requests I'd say is much more important, as
careless reading of streams into memory has at least the potential for a
DOS-attack.

Diez
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

Seebs usenet-nos...@seebs.net writes:

 On 2010-10-06, Diez B. Roggisch de...@web.de wrote:
fkr...@aboutrafi.net23.net writes:
 plz can u convert this cpp file into python i need that badly as soon as 
 possible... I am new to python. I just wanna learn it

 For such an aspiring student of the art of computer programming, I have
 the strange feeling of lack-of-effort-showing here. Do I have to lose my
 faith in youth?

 Never!

 Just be sure you are having faith in them to, well, be youth.  :)

I took the freedom to google a bit. If one can trust people on the
inter-tubes (and who would have heard you can't?), he's a rather skilled
student 

 http://www.aboutrafi.net23.net/

With an impressive amount of technological experience under his belt. So
I'm a bit aghast to see him struggle with this rather simple
problem. Thus my question...

Diez
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: if the else short form

In message i8i1h8$dc...@news.eternal-september.org, BartC wrote:

 I use this syntax where there are two possibilities chosen according to
 condition 'a':
 
 (a | b | c)

Algol 68!

 x = (One,Two,Three) [i-1]
 
 While this works for i = 1,2,3, it goes funny for i=0,-1,-2, and generates
 an error for the rest ...

x = {1 : One, 2 : Two, 3 : Three}.get(i, None Of The Above)
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: [Python-ideas] [Python-Dev] Inclusive Range

In message mailman.1390.1286363672.29448.python-l...@python.org, Antoon 
Pardon wrote:

 Or what if the keys were floats or tuples and I wanted an
 inclusive upper boundary?

If you’re expecting computer floats to behave as mathematically exact 
quantities, you’re asking for trouble.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

On 2010-10-06, Diez B. Roggisch de...@web.de wrote:
 With an impressive amount of technological experience under his belt. So
 I'm a bit aghast to see him struggle with this rather simple
 problem. Thus my question...

It does seem a bit odd.

I mean, if I had a short time line to get something converted to Python,
I'd probably ask for help, but then, I wouldn't take a gig where I needed to
quickly move something into an unfamiliar language.  I'm happily puttering
away slowly at converting a couple of things to Python to get the hang of it,
carefully selecting things with no impending deadlines.

Thus far, I've converted a shell script to Python.  It was... well, shell
turned out to be a poor language for it, but I do note that the shell
script, including all the here documents, was quite a bit smaller than the
Python.  On the other hand, I think the Python script is a lot more
maintainable, and this despite me not really knowing the language particularly
well.  It's an interesting tradeoff.  Still getting used to the Python
way of doing things.

-s
-- 
Copyright 2010, all wrongs reversed.  Peter Seebach / usenet-nos...@seebs.net
http://www.seebs.net/log/ -- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) -- get educated!
I am not speaking for my employer, although they do rent some of my opinions.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

Seebs usenet-nos...@seebs.net writes:

 On 2010-10-06, Diez B. Roggisch de...@web.de wrote:
 With an impressive amount of technological experience under his belt. So
 I'm a bit aghast to see him struggle with this rather simple
 problem. Thus my question...

 It does seem a bit odd.

 I mean, if I had a short time line to get something converted to Python,
 I'd probably ask for help, but then, I wouldn't take a gig where I needed to
 quickly move something into an unfamiliar language.  I'm happily puttering
 away slowly at converting a couple of things to Python to get the hang of it,
 carefully selecting things with no impending deadlines.

From the look of it... he's just trying to get a freebie on a homework
assignment. It certainly is no commercial/useful piece of code
whatsoever... just CS-101 read data from stdin and do stuff.

Diez
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

On 2010-10-06, Diez B. Roggisch de...@web.de wrote:
 From the look of it... he's just trying to get a freebie on a homework
 assignment. It certainly is no commercial/useful piece of code
 whatsoever... just CS-101 read data from stdin and do stuff.

Ooh, I should go help, then.

I *love* to help people on homework.  Although I may not know Python
well enough.

I once responded to a request for a thing that, given a number, says
something like The first digit is 3, the second digit is 2 with a program
that included a partial table of ln(x) for about 30 values between 0 and
900...  It worked, though!

-s
-- 
Copyright 2010, all wrongs reversed.  Peter Seebach / usenet-nos...@seebs.net
http://www.seebs.net/log/ -- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) -- get educated!
I am not speaking for my employer, although they do rent some of my opinions.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

2010-10-06 Thread Grant Edwards

On 2010-10-06, Steven D'Aprano steve-remove-t...@cybersource.com.au wrote:
 On Tue, 05 Oct 2010 23:54:00 -0400, fkrafi wrote:

 plz can u convert this cpp file into python i need that badly as soon as
 possible... I am new to python. I just wanna learn it

 Good grief. It's bad enough to expect us to do your coding for you, 
 without making even the *tiniest* effort to learn yourself, but then to 
 add insult to injury you use text-speak.

 ur nt sending sms now, learn to rite the wrds

LOL!

I was particularly impressed by the pithy subject line.  The extra
exclamation points are always the hallmark of the clueless and rude.

 If you want to learn Python, I suggest you work through some
 tutorials.  Google is your friend: google on python tutorial and
 see what comes up.

-- 
Grant

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: if the else short form

2010-10-06 Thread BartC




Lawrence D'Oliveiro l...@geek-central.gen.new_zealand wrote in message 
news:i8j0dg$lh...@lust.ihug.co.nz...

In message i8i1h8$dc...@news.eternal-september.org, BartC wrote:



x = (One,Two,Three) [i-1]

While this works for i = 1,2,3, it goes funny for i=0,-1,-2, and 
generates

an error for the rest ...


x = {1 : One, 2 : Two, 3 : Three}.get(i, None Of The Above)


Yes, I expected Python to come up with something (it always does).

However,  as I mentioned, one problem here is having to evaluate all the 
items in the list before selecting one:


def fna():
   print FNA CALLED
   return One
def fnb():
   print FNB CALLED
   return Two
def fnc():
   print FNC CALLED
   return Three

i=16
x = {1 : fna(), 2 : fnb(), 3 : fnc()}.get(i, None Of The Above)
print x

Other than efficiency concerns, sometimes you don't want the extra 
side-effects.


Probably there are workarounds here too, but I suspect the syntax won't be 
quite as pert as the Algol68-style example:


x = (i | Zero, One, Two | None of the above)  # 0-based

--
bartc 
--

http://mail.python.org/mailman/listinfo/python-list

Re: if the else short form

2010-10-06 Thread Mel

BartC wrote:

 
 
 Lawrence D'Oliveiro l...@geek-central.gen.new_zealand wrote in message
 news:i8j0dg$lh...@lust.ihug.co.nz...
 In message i8i1h8$dc...@news.eternal-september.org, BartC wrote:
 
 x = (One,Two,Three) [i-1]

 While this works for i = 1,2,3, it goes funny for i=0,-1,-2, and
 generates
 an error for the rest ...

 x = {1 : One, 2 : Two, 3 : Three}.get(i, None Of The Above)
 
 Yes, I expected Python to come up with something (it always does).
 
 However,  as I mentioned, one problem here is having to evaluate all the
 items in the list before selecting one:
 
 def fna():
 print FNA CALLED
 return One
 def fnb():
 print FNB CALLED
 return Two
 def fnc():
 print FNC CALLED
 return Three
 
 i=16
 x = {1 : fna(), 2 : fnb(), 3 : fnc()}.get(i, None Of The Above)
 print x
 
 Other than efficiency concerns, sometimes you don't want the extra
 side-effects.
 
 Probably there are workarounds here too,

The workaround would be (untested)
x = {1: fna, 2: fnb, 3: fnc}.get(i, lambda: None Of The Above) ()

Mel.

-- 
http://mail.python.org/mailman/listinfo/python-list

Re: if the else short form

On Thu, 07 Oct 2010 01:36:33 +0100, BartC wrote:


 However,  as I mentioned, one problem here is having to evaluate all the
 items in the list before selecting one:
 
 def fna():
 print FNA CALLED
 return One
 def fnb():
 print FNB CALLED
 return Two
 def fnc():
 print FNC CALLED
 return Three
 
 i=16
 x = {1 : fna(), 2 : fnb(), 3 : fnc()}.get(i, None Of The Above) 
 print x
 
 Other than efficiency concerns, sometimes you don't want the extra
 side-effects.

Try this instead:

i=16
x = {1 : fna, 2 : fnb, 3 : fnc}.get(i, None Of The Above)()
print x


Also known as the command dispatch pattern.


First class functions are a wonderful thing-ly y'rs, 


-- 
Steven
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Strong typing vs. strong testing

2010-10-06 Thread Pascal J. Bourguignon

Keith H Duggar dug...@alum.mit.edu writes:

 On Sep 29, 9:01 pm, RG rnospa...@flownet.com wrote:
 That the problem is elsewhere in the program ought to be small
 comfort.  But very well, try this instead:

 [...@mighty:~]$ cat foo.c
 #include stdio.h

 int maximum(int a, int b) { return a  b ? a : b; }

 int main() {
   long x = 8589934592;
   printf(Max of %ld and 1 is %d\n, x, maximum(x,1));
   return 0;}

 [...@mighty:~]$ gcc -Wall foo.c
 [...@mighty:~]$ ./a.out
 Max of 8589934592 and 1 is 1

 $ gcc -Wconversion -Werror foo.c
 cc1: warnings being treated as errors
 foo.c: In function 'main':
 foo.c:5: warning: passing argument 1 of 'maximum' with different width
 due to prototype

 It's called learning to compile. And, yes, those warnings (and
 nearly
 every other one) should be enabled and treated as errors if a shop
 wants
 maximum protection. I only wish more (library) vendors did so.

So you're wishing that they'd be active by default.


-- 
__Pascal Bourguignon__ http://www.informatimago.com/
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

On 2010-10-06, fkr...@aboutrafi.net23.net fkr...@aboutrafi.net23.net wrote:
 plz can u convert this cpp file into python i need that badly as soon as
 possible... I am new to python. I just wanna learn it

Having come to realize that this is a homework problem, I would of course
be glad to.

The original program:

#includecstdio

int main()
{
int a[100], n;
freopen(input.txt, r, stdin);
scanf(%d, n);
for(int i=1; i=n; i++)
scanf(%d, a[i]);
return 0;
}

So, let's convert this.

#!/usr/bin/python -w
import cstdio;

def main():
a = [random.randint(-2147483648,2147483647) for i in range(0,100)]
n = random.randint(-2147483648)
sys.stdin = open(input.txt, r)
raise IndexError

I'm not sure how much good this will do you.  It seems to me that you
might get better results translating a program which was not obviously
incorrect.

-s
-- 
Copyright 2010, all wrongs reversed.  Peter Seebach / usenet-nos...@seebs.net
http://www.seebs.net/log/ -- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) -- get educated!
I am not speaking for my employer, although they do rent some of my opinions.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

2010-10-06 Thread John Nagle


On 10/6/2010 8:02 PM, Seebs wrote:

On 2010-10-06,fkr...@aboutrafi.net23.net  fkr...@aboutrafi.net23.net  wrote:

plz can u convert this cpp file into python i need that badly as soon as
possible... I am new to python. I just wanna learn it


Having come to realize that this is a homework problem, I would of course
be glad to.

The original program:

#includecstdio

int main()
{
int a[100], n;
freopen(input.txt, r, stdin);
scanf(%d,n);
for(int i=1; i=n; i++)
scanf(%d,a[i]);
return 0;
}



   This guy doesn't know C very well, either.

   First, scanf was deprecated over five years ago.
And reopening stdin is rarely done, although
it is possible.

   Second, there's a buffer overflow.  n is obtained
from external input, then used to control the for
statement. If N is = 99, there will be a buffer
overflow on a.  Also, starting to fill a from 1
looks like an error.

   Third, the program doesn't actually do anything.
There's no output.

It looks like this approach to C came from

http://beej.us/guide/bgc/output/html/multipage/freopen.html

John Nagle
--
http://mail.python.org/mailman/listinfo/python-list

Re: help!!!

On 2010-10-07, John Nagle na...@animats.com wrote:
 First, scanf was deprecated over five years ago.

It was?  I mean, people have been telling me not to use it since the 80s,
but I wasn't aware that it had been deprecated, except in the sense of being
derided and dismissed as of no value.

-s
-- 
Copyright 2010, all wrongs reversed.  Peter Seebach / usenet-nos...@seebs.net
http://www.seebs.net/log/ -- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) -- get educated!
I am not speaking for my employer, although they do rent some of my opinions.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: list parameter of a recursive function

Diez B. Roggisch wrote:

 Back to your example: your solution is perfectly fine, although a bit
 costly and more error-prone if you happen to forget to create a copy.
 A safer alternative for these cases is using tuples, because they are
 immutable.

Thanks Diez for your explanation.
The problem with tuples is that it is not easy to modify them: in my case, I 
need to append a string to the tuple at each recursive step.
So, it seems to me that I need to write a loop to modify the tuple, because 
on a simple example:

 a=(foo, bar)
 b=(a[0],a[1],toto)
 b
(u'foo', u'bar', u'toto')

I do not find any other means to obtain that result for b. With lists, I can 
use .extend().
Am I right?


-- 
python -c print ''.join([chr(154 - ord(c)) for c in '*9(9(18%.\
91+,\'Z4(55l4('])

When a distinguished but elderly scientist states that something is
possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong. (first law of AC Clarke)
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: list parameter of a recursive function

Steven D'Aprano wrote:

 I think I prefer doing an explicit copy.copy, because it allows to
 remind the reader that it is very important to take care of that.
 
 I think a comment is better for that. It's better to explicitly say
 something is important than to assume the reader will guess.

Yes, you are right.

 Besides, what if the caller wants to supply their own list, and they
 *want* it modified in place rather than a copy made? (I have no idea why
 they might want this, but anything is possible...) You should avoid
 making copies except in methods that are *for* making copies.

My function gives a sensible result only if the list is not modified in 
place. In fact, this list is only used internally for the recursion. That is 
why I have made this function private:

def __relation_loop( sqlite_cursor
, table_name
, crossed_tables = None
, previous_step_link = None
, onetomany_allowed_depth = 1 ):

I give to the user (me!) only access to the public function:

def relation_loop( sqlite_cursor
, table_name
, onetomany_allowed_depth = 1 ):

return __relation_loop( sqlite_cursor
, table_name
, crossed_tables = None
, previous_step_link = None
, onetomany_allowed_depth = onetomany_allowed_depth )

So, crossed_tables and previous_step_link, are only used by the recursion 
process, they are not accessible to the user.

-- 
python -c print ''.join([chr(154 - ord(c)) for c in '*9(9(18%.\
91+,\'Z4(55l4('])

When a distinguished but elderly scientist states that something is
possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong. (first law of AC Clarke)
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: suggestions please what should i watch for/guard against' in a file upload situation?

In message
2ce3860b-ae21-48ae-9abc-cb169a6f1...@e20g2000vbn.googlegroups.com, 
geekbuntu wrote:

 in general, what are things i would want to 'watch for/guard against'
 in a file upload situation?

If you stored the file contents as a blob in a database field, you wouldn’t 
have to worry about filename problems.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Help with sets

In message 87bp79qdhk@rudin.co.uk, Paul Rudin wrote:

 Certainly you can model a set as a dictionary, but that's likely to be
 less efficient than using a set, and quite possibly you'll need to roll
 your own operations on your sets, whereas they're provided for the built
 in implementation.

Did you know that applying the “set” or “frozenset” functions to a dict 
return a set of its keys?

Seems a bit dodgy, somehow.
-- 
http://mail.python.org/mailman/listinfo/python-list

Re: Simple database explorer