Re: Proposal to extend PEP 257 (New Documentation String Spec)
Was tried at least once before:
http://www.python.org/dev/peps/pep-0287/
Check in here with your ideas:
http://www.python.org/community/sigs/current/doc-sig/
Have any other languages mandated the use of a specific documentation markup?
Michael
On Thu, Jul 14, 2011 at 7:02 PM, rantingrick rantingr...@gmail.com wrote:
Hello Folks,
Lately i have been musing over the ideas of method tagging.
Specifically i am referring to method identifiers. As most of you know
i had proposed to add syntactical markers to the language to deal
with the ambiguities that arise whist eyeball parsing sub classed
methods that clobber virtual methods. HOWEVER that idea caused some
fierce controversy within the community, and i can partly understand
why.
Although i strongly believe in proper documentation (even to the point
of forcing syntax on folks) i understand that we cannot implement such
a thing without major growing pains. So with that being said, i have
formulated a new battle plan to defeat this problem of ambiguity.
Unlike most languages out there we have doc-strings; and do we realize
how great this gift is? Sometimes i wonder because you folks should
really be using them like they are going out of style!
As we all know PEP 257 lays out some ground rules for documentation
strings HOWEVER i feel this PEP did no go far enough. Too many folks
are refusing to document properly and so i will take this time to
hammer out a spec. I would like to comments for or against.
---
New Syntax Specification For Documentation Strings
---
{DOC TAG HERE}: {MODULE_NAME|SHORT_SUMMARY_HERE}.
{NEWLINE}
{LONG_DESCRIPTION_HERE}
{NEWLINE}
Arguments: (if applicable)
{ARGUMNET_1} {TYPE}:
ARGUMENT_1_DESCRIPTION}
{ARGUMNET_2} {TYPE}:
ARGUMENT_2 DESCRIPTION}
{ARGUMNET_N} {TYPE}:
ARGUMENT_N_DESCRIPTION}
{NEWLINE}
As you can see my spec introduces some new ideas to writing doc-
strings. Specifically the DOC TAG and {ARG TYPES} are new. Also i've
found it much more useful to separate args and their respective
descriptions with a newline and indention.
---
Example: Module Documentation String.
---
Module simpledialog.py:
This module handles Tkinter dialog boxes.
It contains the following public symbols:
Dialog class:
A base class for dialogs.
askinteger function:
Get an integer from the user.
askfloat function:
Get a float from the user.
askstring function:
Get a string from the user.
I don't know how i feel about marking classes and functions since IF
we follow the python style guide we don;t need to; but that's IF we
FOLLOW it people, IF.
---
Example: Func/Meth Documentation String.
---
def askinteger(parent, title, prompt, **kw):
Interface: Get an integer from the user.
Return value is an integer.
Arguments:
title string:
the dialog title
prompt string|integer|float:
the label text
**kw:
see SimpleDialog class
---
Example: Class Inheritance Documentation Strings.
---
class Base():
def __init__(self):
Internal:
self.m1()
def m1(self, *args):
Overide:
pass
class Derived(Base):
def __init__(self):
Base.__init__(self)
def _m1(self):
Internal: blah
def m1(self):
Clobbered: see Base for detail
def m3(self):
Interface: Blah
---
Tags For Documentation Strings
---
Module:
The module tag is to be used for module doc strings.
Virtual:
The virtual tag is for methods residing in a base class
that are created specifically to be overridden. Of course as we
all know every Python methods/function is virtual by default
however the point of this is to make the code more readable!
Override:
This tag should be placed in a derived class's method which has
clobbered a base method. Typically you can just defer the reader
to look up the base class for more info.
Internal:
This tag should be used on all internal methods (psst: the ones
that
start with a single underscore *ahem* or SHOULD start with a
single
underscore!).
Interface:
This tag is be used for interface method/function doc strings.
This
is probably the most important tag. If you don't do any tagging AT
LEAST tag the interface methods and functions. However i must
remind you that all these tags are very important.
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Re: None versus MISSING sentinel -- request for design feedback
On Fri, Jul 15, 2011 at 3:28 PM, Steven D'Aprano
steve+comp.lang.pyt...@pearwood.info wrote:
My question is, should I accept None as the missing value, or a dedicated
singleton?
In favour of None: it's already there, no extra code required. People may
expect it to work.
Against None: it's too easy to mistakenly add None to a data set by mistake,
because functions return None by default.
I guess the question is: Why are the missing values there? If they're
there because some function returned None because it didn't have a
value to return, and therefore it's a missing value, then using None
as missing would make a lot of sense. But if it's a more explicit
concept of here's a table of values, and the user said that this one
doesn't exist, it'd be better to have an explicit MISSING. (Which I
assume would be exposed as yourmodule.MISSING or something.)
Agreed that float('nan') and and spam are all bad values for
Missings. Possibly should come out as 0, but spam should
definitely fail.
Chris Angelico
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Re: Multiplicity and Asininity in Tkinter Event API
On Fri, Jul 15, 2011 at 8:34 AM, rantingrick rantingr...@gmail.com wrote: KeyPress KeyRelease MouseClick MouseMotion MouseRelease MouseWheel That's it. Go ahead, try to prove me wrong! Does MouseClick mean Mouse Button Down, or does it mean Mouse Button Pressed Then Released Within A Short Time Without The Mouse Moving In Between? Both events are needed. Since you have MouseRelease, I am guessing that it's MouseButtonDown (or MousePress, to parallel your KeyPress/KeyRelease). If you only have MouseDown and MouseUp events (or MousePress and MouseRelease, whatever you wish to call them), then users have a lot of trouble implementing CUA-compliant mouse-click handlers. In the spirit of Ook and its predecessor, I propose one single event: InputEvent. It will have a parameter that specifies the key ID or mouse button that triggered the event; 0 means no key/button, and indicates a mouse movement event. It will contain the location of the mouse, and it's up to the program to keep track of the last known mouse location, to detect movement. The beauty of this system is that programmers can build interfaces that involve pointing at an object, holding the four keys D-R-A-G, and moving the mouse to another location and releasing those keys. This is far more intuitive than the classic mouse-button way of dragging objects around, and avoids the age-old debate of whether to drag with the left or right mouse button. Tkinter should provide this facility so that all new programs will be written with this in mind. Chris Angelico -- http://mail.python.org/mailman/listinfo/python-list
Re: list(), tuple() should not place at Built-in functions in documentation
On Fri, Jul 15, 2011 at 11:32 AM, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: Inside wrote: As telling in the subject,because list and tuple aren't functions,they are types.Is that right? Yes they are types. But they can still be used as functions. Does it matter? Python is duck-typed, even in its documentation. If Python describes something as a function, it means it can be used in place of func in here: result = func(arg1, arg2, arg3) It might be something created with def (a classic function). It might be something created with lambda. It might be an object with a __call__ method. It might be a type. class foo: def __call__(self): return lambda: print(asdf) bar=foo() quux=bar() quux() asdf How many functions are defined here? Chris Angelico -- http://mail.python.org/mailman/listinfo/python-list
Re: Please critique my script
On Fri, Jul 15, 2011 at 4:03 AM, Ellerbee, Edward eeller...@bbandt.com wrote: for makenewlist in range(0,count): sortlist.append(npalist.pop(0) + nxxlist.pop(0)) This can alternatively be done with map(): sortlist = map(lambda x,y: x+y, npalist, nxxlist) However, I'm not sure what your code is meant to do if the two lists have differing numbers of elements (if the two regexps turn up differing numbers of results). If you can assume that this won't happen, the simple map call will do the job. (It would have been a lot cleaner if Python exposed its operators as functions. In Pike, that lambda would simply be `+ (backtick-plus).) Chris Angelico -- http://mail.python.org/mailman/listinfo/python-list
Re: Proposal to extend PEP 257 (New Documentation String Spec)
On Fri, Jul 15, 2011 at 9:02 AM, rantingrick rantingr...@gmail.com wrote: Too many folks are refusing to document properly and so i will take this time to hammer out a spec. The tighter you squeeze your fist, Lord Rick, the more star programmers will slip through your fingers. Make it so docstrings HAVE to be in a particular format, and people will stop writing docstrings. Make it so Python functions HAVE to have docstrings, and people will stop writing Python functions. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Please critique my script
On Jul 15, 8:36 am, Chris Angelico ros...@gmail.com wrote: This can alternatively be done with map(): sortlist = map(lambda x,y: x+y, npalist, nxxlist) (It would have been a lot cleaner if Python exposed its operators as functions. from operator import add -- http://mail.python.org/mailman/listinfo/python-list
Re: list(), tuple() should not place at Built-in functions in documentation
On Jul 15, 4:58 am, Inside fancheyuj...@gmail.com wrote: Hey guy,thx for you feedback first. But I can't follow your opinion.Why?because of the list tuple are placed at built-in function,so before I type 'list' unintentionally on the pyshell and it show me type 'list', I never know that the name 'list' is a type,I used to consider it's a function to produce 'list' type. so,after I figure out this matter,I have to change all my code assert isinstance(someobj, (type([]), type((0, to assert isinstance(someobj, (list, tuple)),that's not a funny job. Are you sure you need such assertions in your code ? -- http://mail.python.org/mailman/listinfo/python-list
Re: list(), tuple() should not place at Built-in functions in documentation
On Jul 15, 9:27 am, bruno.desthuilli...@gmail.com bruno.desthuilli...@gmail.com wrote: On Jul 15, 4:58 am, Inside fancheyuj...@gmail.com wrote: Hey guy,thx for you feedback first. But I can't follow your opinion.Why?because of the list tuple are placed at built-in function,so before I type 'list' unintentionally on the pyshell and it show me type 'list', I never know that the name 'list' is a type,I used to consider it's a function to produce 'list' type. so,after I figure out this matter,I have to change all my code assert isinstance(someobj, (type([]), type((0, to assert isinstance(someobj, (list, tuple)),that's not a funny job. Are you sure you need such assertions in your code ? Sorry, Ben already mentionned this. Need more coffee obviously :-/ -- http://mail.python.org/mailman/listinfo/python-list
Python ++ Operator?
Hello all, I seem something like this on python code: for : for : spam[i][eggs] = ham ++i . . . What's the meaning of using i++? Even, does exist ++ operator in python? Bye -- http://mail.python.org/mailman/listinfo/python-list
Re: list(), tuple() should not place at Built-in functions in documentation
On Thursday, July 14, 2011 8:00:16 PM UTC-7, Terry Reedy wrote: I once proposed, I believe on the tracker, that 'built-in functions' be expanded to 'built-in function and classes'. That was rejected on the basis that people would then expect the full class documentation that is in the 'built-in types' section (which could now be called the built-isssn classes section. Built in functions and contructors? Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
On 15Jul2011 15:28, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: | In favour of None: it's already there, no extra code required. People may | expect it to work. Broadly, I like this one for the reasons you cite. | Against None: it's too easy to mistakenly add None to a data set by mistake, | because functions return None by default. This is a hazard everywhere, but won't such a circumstance normally break lots of stuff anyway? What's an example scenario for getting None by accident but still a bunch of non-None values? The main one I can imagine is a function with a return path that accidentally misses the value something, eg: def f(x): if blah: return 7 ... if foo: return 0 # whoops! I suppose there's no scope for having the append-to-the-list step sanity check for the sentinel (be it None or otherwise)? | In favour of a dedicated MISSING singleton: it's obvious from context. It's | not a lot of work to implement compared to using None. Hard to accidentally | include it by mistake. If None does creep into the data by accident, you | get a nice explicit exception. I confess to being about to discard None as a sentinel in a bit of my own code, but only to allow None to be used as a valid value, using the usual idiom: class IQ(Queue): def __init__(self, ...): self._sentinel = object() ... | Against MISSING: users may expect to be able to choose their own sentinel by | assigning to MISSING. I don't want to support that. Well, we don't have readonly values to play with :-( Personally I'd do what I did above: give it a private name like _MISSING so that people should expect to have inside (and unsupported, unguarenteed) knowledge if they fiddle with it. Or are you publishing the sentinal's name to your callers i.e. may they really return _MISSING legitimately from their functions? Cheers, -- Cameron Simpson c...@zip.com.au DoD#743 http://www.cskk.ezoshosting.com/cs/ What's fair got to do with it? It's going to happen.- Lawrence of Arabia -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
Steven D'Aprano wrote in news:4e1fd009$0$29986$c3e8da3 $54964...@news.astraweb.com in gmane.comp.python.general: I'm designing an API for some lightweight calculator-like statistics functions, such as mean, standard deviation, etc., and I want to support missing values. Missing values should be just ignored. E.g.: mean([1, 2, MISSING, 3]) = 6/3 = 2 rather than 6/4 or raising an error. If you can't make your mind up then maybe you shouldn't: MISSING = MissingObject() def mean( sequence, missing = MISSING ): ... Rob. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python ++ Operator?
2011/7/15 Rafael Durán Castañeda rafadurancastan...@gmail.com: What's the meaning of using i++? Even, does exist ++ operator in python? No it doesn't, which is a good thing. Python differentiates between expressions and variable assignments. i++ in C both assigns the value i + 1 to i AND evaluates to i. Pre and post-increments are almost always confusing unless they are used as the counter-variable inside for-loops. -- mvh/best regards Björn Lindqvist http://www.footballexperts.net/ -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
On Jul 15, 8:08 am, Chris Angelico ros...@gmail.com wrote:
Agreed that float('nan') and and spam are all bad values for
Missings. Possibly should come out as 0
In the face of ambiguity, refuse the temptation to guess.
As far as I'm concerned, I'd expect this to raise a TypeError...
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Re: Python ++ Operator?
2011/7/15 Rafael Durán Castañeda rafadurancastan...@gmail.com: Hello all, What's the meaning of using i++? Even, does exist ++ operator in python? ++i is legal Python but fairly useless. It's the unary + operator, applied twice. It doesn't increment the variable. Now, i+=1 IS valid Python, and WILL do what a C programmer expects it to. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Please critique my script
On Fri, Jul 15, 2011 at 5:19 PM, bruno.desthuilli...@gmail.com bruno.desthuilli...@gmail.com wrote: (It would have been a lot cleaner if Python exposed its operators as functions. from operator import add Ah yes, I forgot that module. Yep, that cleans up the code a bit. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
On Jul 14, 9:46 pm, Billy Mays no...@nohow.com wrote: I noticed that if a file is being continuously written to, the file generator does not notice it: def getLines(f): lines = [] for line in f: lines.append(line) return lines what's wrong with file.readlines() ? -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
On Jul 15, 7:28 am, Steven D'Aprano steve +comp.lang.pyt...@pearwood.info wrote: I'm designing an API for some lightweight calculator-like statistics functions, such as mean, standard deviation, etc., and I want to support missing values. Missing values should be just ignored. E.g.: (snip) Against None: it's too easy to mistakenly add None to a data set by mistake, because functions return None by default. Yeps. In favour of a dedicated MISSING singleton: it's obvious from context. It's not a lot of work to implement compared to using None. Hard to accidentally include it by mistake. If None does creep into the data by accident, you get a nice explicit exception. Against MISSING: users may expect to be able to choose their own sentinel by assigning to MISSING. I don't want to support that. What about allowing users to specificy their own sentinel in the simplest pythonic way: # stevencalc.py MISSING = object() def mean(values, missing=MISSING): your code here Or, if you want to make it easier to specify the sentinel once for the whole API: # stevencalc.py MISSING = object() class Calc(object): def __init__(self, missing=MISSING): self._missing = missing def mean(self, values): # your code here # default: _calc = Calc() mean = _calc.mean # etc... My 2 cents... -- http://mail.python.org/mailman/listinfo/python-list
Re: Python ++ Operator?
2011/7/15 Björn Lindqvist bjou...@gmail.com: Pre and post-increments are almost always confusing unless they are used as the counter-variable inside for-loops. I agree that they're often confusing (i+j) but there are several places where they're handy. array[count++]=value; or the more direct pointer management: *ptr++=value; However, Python doesn't work as close to the bare metal, so it doesn't have such constructs. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Freeze statically
Actually, there is a solution but not very clean. I was surprise by two différent tools: - Statifier (but it needs to be compiled without ASLR) - And ErminePro which is very powerful to transform dynamic executables to static. But if someone is aware about compiling python code to static more properly, I'm in! On Jul 11, 2:24 pm, Sebastien Dudek flux...@gmail.com wrote: Hi everyone! Let me explain you my big adventure. So I trying to make a static python executable using the native Python freeze. I've modified the file Modules/Setup.dist using this perl cli : perl -pi -e 's!(^# \*shared\*)!*static*\n$1!' Modules/Setup.dist Then ./configure, make make install If I'm using my python interpreter to build with freeze a simple project that we can call hello world. It works perfectly but it is still : dynamically linked (uses shared libs). So modifying the Makefile using '-static' for linking, I hopped I could make it static. But... it fail : +-- + ... /home/fluxius/Python-2.7.2/./Modules/pwdmodule.c:156: warning: Using 'setpwent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /home/fluxius/Python-2.7.2/./Modules/pwdmodule.c:168: warning: Using 'endpwent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/bin/ld: dynamic STT_GNU_IFUNC symbol `strcmp' with pointer equality in `/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/ 4.5.2/../../../libc.a(strcmp.o)' can not be used when making an executable; recompile with -fPIE and relink with -pie collect2: ld returned 1 exit status make: *** [hello] Erreur 1 +-- + Help me please!! =) -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
* 2011-07-15T15:28:41+10:00 * Steven D'Aprano wrote: I'm designing an API for some lightweight calculator-like statistics functions, such as mean, standard deviation, etc., and I want to support missing values. Missing values should be just ignored. E.g.: mean([1, 2, MISSING, 3]) = 6/3 = 2 rather than 6/4 or raising an error. My question is, should I accept None as the missing value, or a dedicated singleton? How about accepting anything but ignoring all non-numbers? -- http://mail.python.org/mailman/listinfo/python-list
Re: Installing PyPy alongside Python 2.7 on Windows?
Fair enough. FWIW I have struggled to install binary packages on PyPy on Windows. -- http://mail.python.org/mailman/listinfo/python-list
subprocess isql
Hello Python community, I am working on a project that retrieves data from remote Sybase. I have to use isql and subprocess to do this. Is the following correct? 1. call subprocess.popn to run isql, connect to Sybase 2. run sql (select ...from ...) 3. write retrieved data to subprocess.pipe 4. retrieve data from pipe Did anybody do similar work before? Any ideas (or code piece) to share? Thanks so much. -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
On Jul 15, 9:44 am, Cameron Simpson c...@zip.com.au wrote: On 15Jul2011 15:28, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: | Against MISSING: users may expect to be able to choose their own sentinel by | assigning to MISSING. I don't want to support that. Well, we don't have readonly values to play with :-( Personally I'd do what I did above: give it a private name like _MISSING so that people should expect to have inside (and unsupported, unguarenteed) knowledge if they fiddle with it. I think the point is to allow users to explicitely use MISSING in their data sets, so it does have to be public. But anyway: ALL_UPPER names are supposed to be treated as constants, so the warranty void if messed with still apply. -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
On Jul 15, 10:28 am, Teemu Likonen tliko...@iki.fi wrote: How about accepting anything but ignoring all non-numbers? Totally unpythonic. Better to be explicit about what you expect and crash as loudly as possible when you get anything unexpected. -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
Cameron Simpson wrote: On 15Jul2011 15:28, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: | In favour of None: it's already there, no extra code required. People | may expect it to work. Broadly, I like this one for the reasons you cite. | Against None: it's too easy to mistakenly add None to a data set by | mistake, because functions return None by default. This is a hazard everywhere, but won't such a circumstance normally break lots of stuff anyway? Maybe, maybe not. Either way, it has nothing to do with me -- I only care about what my library does if presented with None in a list of numbers. Should I treat it as a missing value, and ignore it, or treat it as an error? What's an example scenario for getting None by accident but still a bunch of non-None values? The main one I can imagine is a function with a return path that accidentally misses the value something, eg: [code snipped] Yes, that's the main example I can think of. It doesn't really matter how it happens though, only that it is more likely for None to accidentally get inserted into a list than it is for a module-specific MISSING value. My thoughts are, if my library gets presented with two lists: [1, 2, 3, None, 5, 6] [1, 2, 3, mylibrary.MISSING, 5, 6] which is less likely to be an accident rather than deliberate? That's the one I should accept as the missing value. Does anyone think that's the wrong choice? I suppose there's no scope for having the append-to-the-list step sanity check for the sentinel (be it None or otherwise)? It is not my responsibility to validate data during construction, only to do the right thing when given that data. The right thing being, raise an exception if values are not numeric, unless an explicit missing value (whatever that ends up being). | Against MISSING: users may expect to be able to choose their own | sentinel by assigning to MISSING. I don't want to support that. Well, we don't have readonly values to play with :-( Personally I'd do what I did above: give it a private name like _MISSING so that people should expect to have inside (and unsupported, unguarenteed) knowledge if they fiddle with it. Or are you publishing the sentinal's name to your callers i.e. may they really return _MISSING legitimately from their functions? Assuming I choose against None, and go with MISSING, it will be a public part of the library API. The idea being that callers will be responsible for ensuring that if they have data with missing values, they insert the correct sentinel, rather than whatever random non-numeric value they started off with. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
Rob Williscroft wrote: Steven D'Aprano wrote in news:4e1fd009$0$29986$c3e8da3 $54964...@news.astraweb.com in gmane.comp.python.general: I'm designing an API for some lightweight calculator-like statistics functions, such as mean, standard deviation, etc., and I want to support missing values. Missing values should be just ignored. E.g.: mean([1, 2, MISSING, 3]) = 6/3 = 2 rather than 6/4 or raising an error. If you can't make your mind up then maybe you shouldn't: Heh, good point. It's not so much that I can't make up my mind -- I have a preferred solution in mind, but I want to hear what sort of interface for dealing with missing values others expect, and I don't want to prejudice others too greatly. MISSING = MissingObject() def mean( sequence, missing = MISSING ): So you think the right API is to allow the caller to specify what counts as a missing value at runtime? Are you aware of any other statistics packages that do that? -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
On 15Jul2011 20:17, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: | Cameron Simpson wrote: | I suppose there's no scope for having the append-to-the-list step sanity | check for the sentinel (be it None or otherwise)? | | It is not my responsibility to validate data during construction, only to do | the right thing when given that data. The right thing being, raise an | exception if values are not numeric, unless an explicit missing value | (whatever that ends up being). Well there you go. You need to use MISSING, not None. As you say, None can easily be a mistake and you want to be sure. If what you describe as right is right, then I too would be using a special sentinal instead of None. -- Cameron Simpson c...@zip.com.au DoD#743 http://www.cskk.ezoshosting.com/cs/ The English language has a word to describe a group of anarcho-collectivists without resorting to spiffy hyphenated coined phrases: a mob. - Tim Mefford, t...@physics.orst.edu -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
Chris Angelico wrote: On Fri, Jul 15, 2011 at 3:28 PM, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: My question is, should I accept None as the missing value, or a dedicated singleton? In favour of None: it's already there, no extra code required. People may expect it to work. Against None: it's too easy to mistakenly add None to a data set by mistake, because functions return None by default. I guess the question is: Why are the missing values there? If they're there because some function returned None because it didn't have a value to return, and therefore it's a missing value, then using None as missing would make a lot of sense. But if it's a more explicit concept of here's a table of values, and the user said that this one doesn't exist, it'd be better to have an explicit MISSING. (Which I assume would be exposed as yourmodule.MISSING or something.) In general, you have missing values in statistics because somebody wouldn't answer a question, and the Ethics Committee frowns on researchers torturing their subjects to get information. They make you fill out forms. Seriously, missing data is just missing. Unknown. Lost. Not available. Like: NameAge Income Years of schooling == Bill42 150,00016 Susan 23 39,000 14 Karen unknown 89,000 15 Bob 31 0 7 George 79 12,000 unknown Sally 17 19,000 5 Fred66 unknown11 One might still like to calculate the average age as 43. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
* 2011-07-15T03:02:11-07:00 * bruno wrote: On Jul 15, 10:28 am, Teemu Likonen tliko...@iki.fi wrote: How about accepting anything but ignoring all non-numbers? Totally unpythonic. Better to be explicit about what you expect and crash as loudly as possible when you get anything unexpected. Sure, but sometimes an API can be accept anything if any kind of trash is expected. But it seems that not in this case, so you're right. -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
On Fri, Jul 15, 2011 at 8:46 PM, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: In general, you have missing values in statistics because somebody wouldn't answer a question, and the Ethics Committee frowns on researchers torturing their subjects to get information. They make you fill out forms. Which, then, is in support of an explicit User chose not to answer this question MISSING value. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
how to get Python to insert special characters in an xml file?
Hello all. I am currently developing a python application which reads and writes some data to an xml file. I use the elementTree library for doing this. My simple question is that if I have some thing like as in kk company as organisation name, how can I have Python take this as a litteral string including the sign and put in the orgname /orgname tag? Even same applies while reading the file. I would like to have the come as a part of the literal string. Happy hacking. Krishnakant. -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
On 07/15/2011 04:01 AM, bruno.desthuilli...@gmail.com wrote: On Jul 14, 9:46 pm, Billy Maysno...@nohow.com wrote: I noticed that if a file is being continuously written to, the file generator does not notice it: def getLines(f): lines = [] for line in f: lines.append(line) return lines what's wrong with file.readlines() ? Using that will read the entire file into memory which may not be possible. In the library reference, it mentions that using the generator (which calls file.next()) uses a read ahead buffer to efficiently loop over the file. If I call .readline() myself, I forfeit that performance gain. I was thinking that a convenient solution to this problem would be to introduce a new Exception call PauseIteration, which would signal to the caller that there is no more data for now, but not to close down the generator entirely. -- Bill -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
Am 14.07.2011 21:46 schrieb Billy Mays: I noticed that if a file is being continuously written to, the file generator does not notice it: Yes. That's why there were alternative suggestions in your last thread How to write a file generator. To repeat mine: an object which is not an iterator, but an iterable. class Follower(object): def __init__(self, file): self.file = file def __iter__(self): while True: l = self.file.readline() if not l: return yield l if __name__ == '__main__': import time f = Follower(open(/var/log/messages)) while True: for i in f: print i, print all read, waiting... time.sleep(4) Here, you iterate over the object until it is exhausted, but you can iterate again to get the next entries. The difference to the file as iterator is, as you have noticed, that once an iterator is exhausted, it will be so forever. But if you have an iterable, like the Follower above, you can reuse it as you want. -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
Chris Angelico wrote: On Fri, Jul 15, 2011 at 8:46 PM, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: In general, you have missing values in statistics because somebody wouldn't answer a question, and the Ethics Committee frowns on researchers torturing their subjects to get information. They make you fill out forms. Which, then, is in support of an explicit User chose not to answer this question MISSING value. Well yes, but None is an explicit missing value too. The question I have is if I should support None as that value, or something else. Or if anyone can put a good case for it, both, or neither and so something completely different. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
On 07/15/2011 08:39 AM, Thomas Rachel wrote: Am 14.07.2011 21:46 schrieb Billy Mays: I noticed that if a file is being continuously written to, the file generator does not notice it: Yes. That's why there were alternative suggestions in your last thread How to write a file generator. To repeat mine: an object which is not an iterator, but an iterable. class Follower(object): def __init__(self, file): self.file = file def __iter__(self): while True: l = self.file.readline() if not l: return yield l if __name__ == '__main__': import time f = Follower(open(/var/log/messages)) while True: for i in f: print i, print all read, waiting... time.sleep(4) Here, you iterate over the object until it is exhausted, but you can iterate again to get the next entries. The difference to the file as iterator is, as you have noticed, that once an iterator is exhausted, it will be so forever. But if you have an iterable, like the Follower above, you can reuse it as you want. I did see it, but it feels less pythonic than using a generator. I did end up using an extra class to get more data from the file, but it seems like overhead. Also, in the python docs, file.next() mentions there being a performance gain for using the file generator (iterator?) over the readline function. Really what would be useful is some sort of PauseIteration Exception which doesn't close the generator when raised, but indicates to the looping header that there is no more data for now. -- Bill -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
On Fri, Jul 15, 2011 at 10:52 PM, Billy Mays no...@nohow.com wrote: Really what would be useful is some sort of PauseIteration Exception which doesn't close the generator when raised, but indicates to the looping header that there is no more data for now. All you need is a sentinel yielded value (eg None). ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
Steven D'Aprano wrote: Well yes, but None is an explicit missing value too. The question I have is if I should support None as that value, or something else. Or if anyone can put a good case for it, both, or neither and so something completely different. If it's any help, I think (some of?) the database interface packages already do just that, returning None when they find NULL fields. Mel. -- http://mail.python.org/mailman/listinfo/python-list
Re: subprocess isql
peterff66 peterf...@yahoo.com wrote in message
news:ivo9or+j...@egroups.com...
Hello Python community,
I am working on a project that retrieves data from remote Sybase. I have
to use isql and subprocess to do this. Is the following correct?
1. call subprocess.popn to run isql, connect to Sybase
2. run sql (select ...from ...)
3. write retrieved data to subprocess.pipe
4. retrieve data from pipe
Did anybody do similar work before? Any ideas (or code piece) to share?
I did something vaguely similar a while ago. I don't know how helpful this
will be, but it may give you some ideas.
Firstly, these are the main differences between your scenario and mine -
1. I was using 'osql' to connect to MS SQL Server.
2. I used os.popen4, not subprocess. Hopefully you can follow the guidelines
in the manual to translate to subprocess.
3. In my case, I built up a long command to create and populate various
database tables using StringIO, passed the string to popen4.stdout, and then
read popen4.stdin and displayed it on the screen to read any output.
4. On looking at my code, I see that I started a sub-thread to read
popen4.stdin. I can't remember why I did that, but it may have been
something to do with getting the output in realtime instead of waiting for
the command to finish executing.
Here is the code that I used -
import os
import threading
from cStringIO import StringIO
def read_stdout(stdout):
while True:
line = stdout.readline()
if not line:
break
print line
os.environ['OSQLPASSWORD'] = pwd
sql_stdin, sql_stdout = os.popen4('osql -U %s -d %s -n' % (user,
database))
s = StringIO()
[call function to build up commands]
threading.Thread(target=read_stdout, args=(sql_stdout,)).start()
s.seek(0)
sql_stdin.writelines(s.readlines())
s.close()
sql_stdin.close()
HTH
Frank Millman
--
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Re: Multiplicity and Asininity in Tkinter Event API
On Jul 15, 1:17 am, Chris Angelico ros...@gmail.com wrote: On Fri, Jul 15, 2011 at 8:34 AM, rantingrick rantingr...@gmail.com wrote: KeyPress KeyRelease MouseClick MouseMotion MouseRelease MouseWheel That's it. Go ahead, try to prove me wrong! Does MouseClick mean Mouse Button Down, or does it mean Mouse Button Pressed Then Released Within A Short Time Without The Mouse Moving In Between? Both events are needed. NO these six sequences are ALL you need! I suppose you are suggesting that you will be unable to detect when the mouse is repeat-firing or when you want to detect groups of rapid-succession clicks (double, triple, etc)? This info is contained in the 'event' object passed to the handler by Tkinter. if event.time [] lasttime: blah if event.repeat: blah By removing all the unnessary sequence combinations you create readable code and ease the leaning curve. Since you have MouseRelease, I am guessing that it's MouseButtonDown (or MousePress, to parallel your KeyPress/KeyRelease). Ok Mr. Pedantic. I suppose for unity sake we should use the sequence name MousePress instead of MouseClick. I'll give you that one. -- http://mail.python.org/mailman/listinfo/python-list
Re: Multiplicity and Asininity in Tkinter Event API
On Fri, Jul 15, 2011 at 11:54 PM, rantingrick rantingr...@gmail.com wrote: Ok Mr. Pedantic. I suppose for unity sake we should use the sequence name MousePress instead of MouseClick. I'll give you that one. It is very significant; if you call it Click, people will assume it means Press, Release within a certain maximum time and without more than a maximum amount of movement (in some cases 0 movement, others permit a mickey or two). Yes, that's all that's actually needed. But if you force programmers to process the low-level events, you put load on them that they don't need. It's possible to define every program in terms of a handful of operations - do you want to ditch all of Python's rich syntax and library in favour of that? ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: how to get Python to insert special characters in an xml file?
On Jul 15, 2011, at 7:53 AM, hackingKK wrote: Hello all. I am currently developing a python application which reads and writes some data to an xml file. I use the elementTree library for doing this. My simple question is that if I have some thing like as in kk company as organisation name, how can I have Python take this as a litteral string including the sign and put in the orgname /orgname tag? Even same applies while reading the file. I would like to have the come as a part of the literal string. Hi Krishnakant, You don't need to do anything special to insert metacharacters like and and into XML using ElementTree. Just treat them as normal text and ElementTree will change them to entity references (amp;, etc.) when it writes your file to disk. If you're having a specific problem with this, post some code. Cheers Philip -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
Am 15.07.2011 14:26 schrieb Billy Mays: I was thinking that a convenient solution to this problem would be to introduce a new Exception call PauseIteration, which would signal to the caller that there is no more data for now, but not to close down the generator entirely. Alas, an exception thrown causes the generator to stop. Thomas -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
Am 15.07.2011 14:52 schrieb Billy Mays: Also, in the python docs, file.next() mentions there being a performance gain for using the file generator (iterator?) over the readline function. Here, the question is if this performance gain is really relevant AKA feelable. The file object seems to have another internal buffer distinct from the one used for iterating used for the readline() function. Why this is not the same buffer is unclear to me. Really what would be useful is some sort of PauseIteration Exception which doesn't close the generator when raised, but indicates to the looping header that there is no more data for now. a None or other sentinel value would do this as well (as ChrisA already said). Thomas -- http://mail.python.org/mailman/listinfo/python-list
Re: subprocess isql
On 15 Jul, 04:47, peterff66 peterf...@yahoo.com wrote: I am working on a project that retrieves data from remote Sybase. I have to use isql and subprocess to do this. Is the following correct? I once had to hammer a nail, but I had to use a screw driver. Didn't work. Did anybody do similar work before? Any ideas (or code piece) to share? Nobody has ever used Python to connect with an SQL database before. There is no Python database API, and no Sybase module. -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
On 07/15/2011 10:28 AM, Thomas Rachel wrote: Am 15.07.2011 14:52 schrieb Billy Mays: Also, in the python docs, file.next() mentions there being a performance gain for using the file generator (iterator?) over the readline function. Here, the question is if this performance gain is really relevant AKA feelable. The file object seems to have another internal buffer distinct from the one used for iterating used for the readline() function. Why this is not the same buffer is unclear to me. Really what would be useful is some sort of PauseIteration Exception which doesn't close the generator when raised, but indicates to the looping header that there is no more data for now. a None or other sentinel value would do this as well (as ChrisA already said). Thomas A sentinel does provide a work around, but it also passes the problem onto the caller rather than the callee: def getLines(f): lines = [] while True: yield f.readline() def bar(f): for line in getLines(f): if not line: # I now have to check here instead of in getLines break foo(line) def baz(f): for line in getLines(f) if line: # this would be nice for generators foo(line) bar() is the correct way to do things, but I think baz looks cleaner. I found my self writing baz() first, finding it wasn't syntactically correct, and then converting it to bar(). The if portion of the loop would be nice for generators, since it seems like the proper place for the sentinel to be matched. Also, with potentially infinite (but pauseable) data, there needs to be a nice way to catch stuff like this. -- Bill -- http://mail.python.org/mailman/listinfo/python-list
Re: Proposal to extend PEP 257 (New Documentation String Spec)
Em sexta-feira, 15 de julho de 2011 04:13:43, Chris Angelico escreveu: On Fri, Jul 15, 2011 at 9:02 AM, rantingrickrantingr...@gmail.com wrote: Too many folks are refusing to document properly and so i will take this time to hammer out a spec. The tighter you squeeze your fist, Lord Rick, the more star programmers will slip through your fingers. Make it so docstrings HAVE to be in a particular format, and people will stop writing docstrings. Make it so Python functions HAVE to have docstrings, and people will stop writing Python functions. ChrisA I'm with Chris. If you mandate this sort of things on the programmer this will just go downhill. George -- George Rodrigues da Cunha Silva Desenvolvedor GIS http://geoprocessamento.net http://blog.geoprocessamento.net -- http://mail.python.org/mailman/listinfo/python-list
Python 2.6.6 on Windows 7 problem - ImportError: No module named site
Hello! If I start python -v, I get # installing zipimport hook import zipimport # builtin # installed zipimport hook 'import site' failed; traceback ImportError: No module named site Entering any command yields LookupError: no codec search functions registered: can't find encoding I reinstalled it, but this makes no difference. Any suggestions? Thanks Mark -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
On Thu, Jul 14, 2011 at 11:28 PM, Steven D'Aprano
steve+comp.lang.pyt...@pearwood.info wrote:
Hello folks,
I'm designing an API for some lightweight calculator-like statistics
functions, such as mean, standard deviation, etc., and I want to support
missing values. Missing values should be just ignored. E.g.:
mean([1, 2, MISSING, 3]) = 6/3 = 2 rather than 6/4 or raising an error.
My question is, should I accept None as the missing value, or a dedicated
singleton?
In favour of None: it's already there, no extra code required. People may
expect it to work.
Against None: it's too easy to mistakenly add None to a data set by mistake,
because functions return None by default.
Good point.
In favour of a dedicated MISSING singleton: it's obvious from context. It's
not a lot of work to implement compared to using None. Hard to accidentally
include it by mistake. If None does creep into the data by accident, you
get a nice explicit exception.
Also good points.
Against MISSING: users may expect to be able to choose their own sentinel by
assigning to MISSING. I don't want to support that.
I've considered what other packages do:-
R uses a special value, NA, to stand in for missing values. This is more or
less the model I wish to follow.
I believe that MATLAB treats float NANs as missing values. I consider this
an abuse of NANs and I won't be supporting that :-P
I was just thinking of this. :)
Spreadsheets such as Excel, OpenOffice and Gnumeric generally ignore blank
cells, and give you a choice between ignoring text and treating it as zero.
E.g. with cells set to [1, 2, spam, 3] the AVERAGE function returns 2 and
the AVERAGEA function returns 1.5.
numpy uses masked arrays, which is probably over-kill for my purposes; I am
gratified to see it doesn't abuse NANs:
import numpy as np
a = np.array([1, 2, float('nan'), 3])
np.mean(a)
nan
numpy also treats None as an error:
a = np.array([1, 2, None, 3])
np.mean(a)
Traceback (most recent call last):
File stdin, line 1, in module
File /usr/lib/python2.5/site-packages/numpy/core/fromnumeric.py, line
860, in mean
return mean(axis, dtype, out)
TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'
I would appreciate any comments, advice or suggestions.
Too bad there isn't a good way to freeze a name, i.e. indicate that
any attempt to rebind it is an exception. Trying to rebind None is a
SyntaxError, but a NameError or something would be fine. Then the
downside of using your own sentinel here goes away.
In reality, using Missing may be your best bet anyway. If there were
a convention for indicating a name should not be re-bound (like a
single leading underscore indicates private), you could use that
(all caps?). Since we're all consenting adults it would probably be
good enough to make sure others know that Missing should not be
re-bound...
I might have said to use NotImplemented instead of None, but it can be
re-bound and the name isn't as helpful for your use case.
Another solution, perhaps ugly or confusing, is to use something like
two underscores as the name for your sentinel:
mean([1, 2, __, 3])
Still it seems like using Missing (or whatever) would be better than None.
-eric
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
--
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Re: None versus MISSING sentinel -- request for design feedback
Mel wrote: Steven D'Aprano wrote: Well yes, but None is an explicit missing value too. The question I have is if I should support None as that value, or something else. Or if anyone can put a good case for it, both, or neither and so something completely different. If it's any help, I think (some of?) the database interface packages already do just that, returning None when they find NULL fields. Indeed. I'm adding Null support to my dbf package now, and while some of the return values (Logical, Date, DateTime, and probably Character) will have their own dedicated singletons (Null, NullDate, NullDateTime, NullChar -- which will all compare equal to None) the numeric values will be None... although, now that I've seen this thread, I'll add the ability to choose what the numeric Null is returned as. ~Ethan~ -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
Steven D'Aprano wrote: Rob Williscroft wrote: MISSING = MissingObject() def mean( sequence, missing = MISSING ): So you think the right API is to allow the caller to specify what counts as a missing value at runtime? Are you aware of any other statistics packages that do that? R does it, not in the stats functions itself but in, for instance read.table. When reading data from an external file, you can specify a set of values that will be converted to NA in the resulting data frame. I think it's worth considering this approach, namely separating the input of the data into your system from the calculations on that data. You haven't said exactly how people are going to be using your API, but your example of where mising data comes from showed something like a table of data from a survey. If this is the case, and users are going to be importing sets of data from external files, it makes a lot of sense to let them specify convert these particular values to MISSING when importing. Either way, my answer to your original question would be: if you want to err on the side of caution, use your own MISSING value and just provide a simple function that will MISSING-ize specified values: def ckeanUp(data, missing=None): if missing is None: missing = [] return [d for d in data if d not in missing else MISSING] (Yet another use of None here! :-) Then if people find their functions are returning None (or any other value, such as an empty string) to mean a genuine missing value, they can just wrap the call in this cleanUp function. The reverse is harder to do: if you use None as your missing-value sentinel, you irrevocably lose the ability to tell it apart from other uses of None. -- --OKB (not okblacke) Brendan Barnwell Do not follow where the path may lead. Go, instead, where there is no path, and leave a trail. --author unknown -- http://mail.python.org/mailman/listinfo/python-list
Re: Proposal to extend PEP 257 (New Documentation String Spec)
On Jul 15, 2:13 am, Chris Angelico ros...@gmail.com wrote: On Fri, Jul 15, 2011 at 9:02 AM, rantingrick rantingr...@gmail.com wrote: Too many folks are refusing to document properly and so i will take this time to hammer out a spec. The tighter you squeeze your fist, Lord Rick, the more star programmers will slip through your fingers. Make it so docstrings HAVE to be in a particular format, and people will stop writing docstrings. Make it so Python functions HAVE to have docstrings, and people will stop writing Python functions. Hmm, that's strange considering that code MUST be formatted in certain ways or you get a syntax error (indention, colons, parenthesis, etc, etc). I don't hear the masses claiming that they are going over to Ruby simply because of indention. In my mind doc-strings should ALWAYS be optional HOWEVER if the programmer decides to create a doc-string THEN he must observe some syntax rules or his code will throw an SyntaxError. Remember, freedom is good, unbridled freedom is the root of all evil. So what's so terrible about structure Chris? Nobody's freedom are being taken away. You don't HAVE to create doc-strings, just like you don't HAVE to code with Python (you do free form formatting Ruby). Python is a language that is meant to be clean. Forced indention makes that possible. Forced doc-string syntax will complete the circle. -- http://mail.python.org/mailman/listinfo/python-list
Looking for general advice on complex program
Maybe not to the gurus here, but for me, this is a complex problem and I want to make sure I understand the real problem. All of this is in Python 2.7 and wxPython I have several XML files on a shared drive. I have applications on other machines that need to access this XML file. These applications need to read and write to this file. These applications need to a) be alerted to a file change, or b) monitor the file for changes and regular intervals. In my code, I have XManager classes (using a Singleton pattern) that reads each XML file into a tree (using ElementTree). The XManager class can read the file, make changes to the tree, and write the file as needed. Now I'm expanding to the multiple application level, and I think I understand what I need to do, and I'm unsure about the exact processes. I've been trying to have the XManagers check periodically if the XML file they monitor has changed. Since I don't want to mess up the GUI with constant hanging, I think I can use the thread or threading modules to create a recurring timed check, and then I need a separate check to see if the file is in use before reading or writing. I also need, I think, to have a way to check if the GUI is editing a node before the XManager reads the file, so the thread needs to be interrupted, or paused, because I don't know if threads would stop if a wxDialog is being show modally or not. So, am I on the right track here? josh -- http://mail.python.org/mailman/listinfo/python-list
Re: Looking for general advice on complex program
On 07/15/2011 03:47 PM, Josh English wrote: I remember reading that file locking doesn't work on network mounted drives (specifically nfs mounts), but you might be able to simply create a 'lock' (mydoc.xml.lock or the like) file for the XML doc in question. If that file exists you could either hang or silently give up. Not sure if that helps. -- Bill -- http://mail.python.org/mailman/listinfo/python-list
Re: list(), tuple() should not place at Built-in functions in documentation
Why I use assertion,please check this code: class User(object):pass class Student(User):pass class Professional(User):pass def add(user): assert(user, User) def add(users): assert(users, (tuple, list)) #If necessary I'll also check every obj in the sequence to see whether it's a User. I just follow some coding rules of me: 1. Controlling input strictly. 2. In a function keep doubting on its parameters until they're checked. 3. Let potential errors raise as early as possible. -- http://mail.python.org/mailman/listinfo/python-list
OpenCV Object Detection
Hi all.. what is the best way (using OpenCV) to go about detecting objects by color? Specifically, I need to detect multiple objects - first, a main object (a coin), then multiple objects within that main (green particles on the coin). I'm finding lots of info about facial recognition, but not much in the way of just detecting by color. In this case, the coin will always be silver and the particles contained on it will always be some shade of green. Accuracy is very important - which is why I figured detecting via color would be the way to go. My goal is to detect as close to the exact size of the coin/particles as possible. That said, if there are more accurate ways out there I'm open to suggestions! Thanks in advance. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python ++ Operator?
On Fri, Jul 15, 2011 at 1:06 AM, Chris Angelico ros...@gmail.com wrote: 2011/7/15 Björn Lindqvist bjou...@gmail.com: Pre and post-increments are almost always confusing unless they are used as the counter-variable inside for-loops. I agree that they're often confusing (i+j) but there are several places where they're handy. array[count++]=value; or the more direct pointer management: *ptr++=value; However, Python doesn't work as close to the bare metal, so it doesn't have such constructs. I don't regard this as a low level versus VHLL issue - I regard it as a matter of operators with side effects being too error prone. Adding such operators to Python has been discussed (it'd almost certainly be easy to add), and rejected. BTW, array operations optimize to the same thing as pointer arithmetic in most C compilers, but the latter tends to be less clear. -- http://mail.python.org/mailman/listinfo/python-list
Python threading/multiprocessing issue.
I'm working on a tool that runs a number of process is separate thread. I've, up to this point, been using threading.Thread, but from what I read multiprocess will allow multiple processors to be used From the python docs on multiprocessing. Due to this, the multiprocessing module allows the programmer to fully leverage multiple processors on a given machine. I have run into an issue when modifying the thread object from the run method. Threading.thread allows me to change an attribute in the run method and it hold while multiprocessing.Process loses it. Here is an example illustrating the inconsistency that I've seen. -- | import time import multiprocessing import threading def simple_process_call(): my_process = SimpleProcess() my_process.start() while not my_process.done.is_set(): pass print my_process.my_attribute class SimpleProcess(multiprocessing.Process): def __init__(self): super(SimpleProcess, self).__init__() self.my_attribute = 'Fail' self.done = multiprocessing.Event() def run(self): self.my_attribute = 'Success' time.sleep(5) self.done.set() def simple_thread_call(): my_thread = SimpleThread() my_thread.start() while not my_thread.done.is_set(): pass print my_thread.my_attribute class SimpleThread(threading.Thread): def __init__(self): super(SimpleThread, self).__init__() self.my_attribute = 'Fail' self.done = threading.Event() def run(self): self.my_attribute = 'Success' time.sleep(5) self.done.set() if __name__ == '__main__': # simple_process_call() simple_thread_call()| -- The odd thing is that I can modify the multiprocessing.Event and it holds, but modifying any attribute on the class goes away. If I am super ignorant of something, please cure me of it. Thanks in advance! Brandon L. Harris -- http://mail.python.org/mailman/listinfo/python-list
Re: Python ++ Operator?
In article mailman.1055.1310716536.1164.python-l...@python.org
Chris Angelico ros...@gmail.com wrote:
2011/7/15 Rafael Durán Castañeda rafadurancastan...@gmail.com:
Hello all,
What's the meaning of using i++? Even, does exist ++ operator in python?
++i is legal Python but fairly useless. It's the unary + operator,
applied twice. It doesn't increment the variable.
Well...
class Silly:
def __init__(self, value):
self.value = value
self._pluscount = 0
def __str__(self):
return str(self.value)
def __pos__(self):
self._pluscount += 1
if self._pluscount == 2:
self.value += 1
self._pluscount = 0
return self
def main():
i = Silly(0)
print('initially, i = %s' % i)
print('plus-plus i = %s' % ++i)
print('finally, i = %s' % i)
main()
:-)
(Of course, +i followed by +i *also* increments i...)
--
In-Real-Life: Chris Torek, Wind River Systems
Intel require I note that my opinions are not those of WRS or Intel
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
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Re: Possible File iteration bug
Am 15.07.2011 16:42 schrieb Billy Mays: A sentinel does provide a work around, but it also passes the problem onto the caller rather than the callee: That is right. BTW, there is another, maybe easier way to do this: for line in iter(f.readline, ''): do_stuff(line) This provides an iterator which yields return values from the given callable until '' is returned, in which case the iterator stops. As caller, you need to have knowledge about the fact that you can always continue. The functionality which you ask for COULD be accomplished in two ways: Firstly, one could simply break the contract of an iterator (which would be a bad thing): just have your next() raise a StopIteration and then continue nevertheless. Secondly, one could do a similiar thing and have the next() method raise a different exception. Then the caller has as well to know about, but I cannot find a passage in the docs which prohibit this. I just have tested this: def r(x): return x def y(x): raise x def l(f, x): return lambda: f(x) class I(object): def __init__(self): self.l = [l(r, 1), l(r, 2), l(y, Exception), l(r, 3)] def __iter__(self): return self def next(self): if not self.l: raise StopIteration c = self.l.pop(0) return c() i = I() try: for j in i: print j except Exception, e: print E:, e print tuple(i) and it works. So I think it COULD be ok to do this: class NotNow(Exception): pass class F(object): def __init__(self, f): self.file = f def __iter__(self): return self def next(self): l = self.file.readline() if not l: raise NotNow return l f = F(file(/var/log/messages)) import time while True: try: for i in f: print , i, except NotNow, e: print pause time.sleep(1) HTH, Thomas -- http://mail.python.org/mailman/listinfo/python-list
Re: Python threading/multiprocessing issue.
I'm working on a tool that runs a number of process is separate thread. I've, up to this point, been using threading.Thread, but from what I read multiprocess will allow multiple processors to be used From the python docs on multiprocessing. Due to this, the multiprocessing module allows the programmer to fully leverage multiple processors on a given machine. I have run into an issue when modifying the thread object from the run method. Threading.thread allows me to change an attribute in the run method and it hold while multiprocessing.Process loses it. I am not a multiprocessing expert, but I think the problem you are having is that Process is running your code in a separate process, so there is no way you could see those object changes in your main line code. In other words, Process is not an exact replacement for Thread. If you need to communicate between the different parts, you would want to use the abstractions provided by Queue or Pipe. Keep reading down the multiprocessing page in the docs until you get to Exchanging objects between processes: http://docs.python.org/library/multiprocessing.html#exchanging-objects-between-processes Sharing state between processes seems like it will be especially relevant to what you are doing: http://docs.python.org/library/multiprocessing.html#sharing-state-between-processes Basically, it says don't do that :o) Here is an example illustrating the inconsistency that I've seen. One thing that would help here is a sample of what output you get from your code, and what you were hoping to get. -- http://mail.python.org/mailman/listinfo/python-list
Re: list(), tuple() should not place at Built-in functions in documentation
Terry Reedy, 15.07.2011 05:00: On 7/14/2011 9:51 PM, Ben Finney wrote: Steven D'Aprano writes: Inside wrote: As telling in the subject,because list and tuple aren't functions,they are types.Is that right? At one time (before 2.2), they were functions and not classes. They are still functions in the sense that you can call them (with or without arguments) and get a result back. The exact distinction can be considered an implementation detail in most contexts. There are even extreme cases that render the distinction completely useless. Think of type(), for example. In its exceedingly most common use case, it does *not* create a type, even if it's a call to a type constructor. Something similar applies to a no-args call to tuple(), which does not create a new object in CPython, but only returns a new reference to a singleton. Types in Python are allowed to do these things, so it's not always meaningful to distinguish between typeX() being a call to a type or a function. Yes they are types. But they can still be used as functions. Does it matter? As a newcomer to the documentation I looked fruitlessly in the table of contents for a section that would contain the built-in types. “Built-in functions” was eliminated for the reason the OP states. I think it matters. (But I haven't proposed a documentation patch for it.) I once proposed, I believe on the tracker, that 'built-in functions' be expanded to 'built-in function and classes'. That was rejected on the basis that people would then expect the full class documentation that is in the 'built-in types' section (which could now be called the built-isssn classes section. A more exact title would be 'built-in callables', but that would be even less helpful to newcomers. Callables are functions in the generic sense. I think function is about the best expected and newcomer-friendly name one can give to a callable, especially in the context of a duck-typed, protocol-oriented language like Python. The section title in question describes perfectly its contents. It's a different question if a separate section like here's a list of reference to the descriptions of types that Python provides in its builtins is required. But I think we have that already. In any case, the new index makes it easy to see what is in that chapter. Agreed. Stefan -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
Billy Mays wrote: A sentinel does provide a work around, but it also passes the problem onto the caller rather than the callee The callee can easily take care of it -- just block until more is ready. If blocking is not an option, then the caller has to deal with it no matter how callee is implemented -- an exception, a sentinel, or some signal that says nope, nothing for ya! try back later! ~Ethan~ -- http://mail.python.org/mailman/listinfo/python-list
Re: Python ++ Operator?
Chris Angelico, 15.07.2011 10:06: 2011/7/15 Björn Lindqvist: Pre and post-increments are almost always confusing unless they are used as the counter-variable inside for-loops. I agree that they're often confusing (i+j) but there are several places where they're handy. array[count++]=value; or the more direct pointer management: *ptr++=value; More direct, sure. But readable? Well, only when you know what this specific pattern does. If you have to think about it, it may end up hurting your eyes before you figure it out. Stefan -- http://mail.python.org/mailman/listinfo/python-list
Re: Python threading/multiprocessing issue.
I see. Well I was hoping to see the same result in the multiprocessing example as using the threading example. What you pointed out makes sense though, but what I don't understand is how modifying the queue in the example works fine in both. Possibly it was designed for that kind of use? Brandon L. Harris On 07/15/2011 03:55 PM, Lee Harr wrote: I'm working on a tool that runs a number of process is separate thread. I've, up to this point, been using threading.Thread, but from what I read multiprocess will allow multiple processors to be used From the python docs on multiprocessing. Due to this, the multiprocessing module allows the programmer to fully leverage multiple processors on a given machine. I have run into an issue when modifying the thread object from the run method. Threading.thread allows me to change an attribute in the run method and it hold while multiprocessing.Process loses it. I am not a multiprocessing expert, but I think the problem you are having is that Process is running your code in a separate process, so there is no way you could see those object changes in your main line code. In other words, Process is not an exact replacement for Thread. If you need to communicate between the different parts, you would want to use the abstractions provided by Queue or Pipe. Keep reading down the multiprocessing page in the docs until you get to Exchanging objects between processes: http://docs.python.org/library/multiprocessing.html#exchanging-objects-between-processes Sharing state between processes seems like it will be especially relevant to what you are doing: http://docs.python.org/library/multiprocessing.html#sharing-state-between-processes Basically, it says don't do that :o) Here is an example illustrating the inconsistency that I've seen. One thing that would help here is a sample of what output you get from your code, and what you were hoping to get. -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
On 7/15/2011 6:19 AM, Steven D'Aprano wrote: Use None as default. Requiring users to use your special value would be a nuisance. They may have data prepared separately from your module. Rob Williscroft wrote: MISSING = MissingObject() def mean( sequence, missing = MISSING ): This is also a good idea. So you think the right API is to allow the caller to specify what counts as a missing value at runtime? Are you aware of any other statistics packages that do that? AFAIK, standard feature on major packages. BMDP, SAS and SPSS as I remember. Missing values could be specified on a per column basis. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
On 7/15/2011 8:26 AM, Billy Mays wrote: On 07/15/2011 04:01 AM, bruno.desthuilli...@gmail.com wrote: On Jul 14, 9:46 pm, Billy Maysno...@nohow.com wrote: I noticed that if a file is being continuously written to, the file generator does not notice it: def getLines(f): lines = [] for line in f: lines.append(line) return lines what's wrong with file.readlines() ? Using that will read the entire file into memory which may not be So will getLines. possible. In the library reference, it mentions that using the generator (which calls file.next()) uses a read ahead buffer to efficiently loop over the file. If I call .readline() myself, I forfeit that performance gain. Are you sure? Have you measured the difference? -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: difflib-like library supporting moved blocks detection?
2011/7/14 Chris Torek nos...@torek.net:
In article mailman.1002.1310591600.1164.python-l...@python.org
Vlastimil Brom vlastimil.b...@gmail.com wrote:
I'd like to ask about the availability of a text diff library, like
difflib, which would support the detection of moved text blocks.
If you allow arbitrary moves, the minimal edit distance problem
(string-to-string edit) becomes substantially harder. If you only
allow insert, delete, or in-place-substitute, you have what is
called the Levenshtein distance case. If you allow transpositions
you get Damerau-Levenshtein. These are both solveable with a
dynamic programming algorithm. Once you allow move operations,
though, the problem becomes NP-complete.
See http://pages.cs.brandeis.edu/~shapird/publications/JDAmoves.pdf
for instance. (They give an algorithm that produces usually
acceptable results in polynomial time.)
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In-Real-Life: Chris Torek, Wind River Systems
Thanks for the references and explanation!
I do realise the added complexity with taking the moves into account;
given that, my current needs and the usually satisfying results
obtained easily with difflib, I am not going to try to implement some
more complex diffing algorithm.
However, it turns out that the mentioned naive approach with just
recomparing the text additions and removals may be partially viable -
with some luck, i.e. given, the relevant segments are identified as
deletions and inserts and isolated by difflib in the first place (and
not subsumed under larger changes or split).
For illustration, the rough simplified code is attached (sorry for the
style and possible quirks...)
Just now the more similar text segments are just collected, it would
be also possible to sort them on their similarity ratio; the current
approach also allows to highlight potentially multiple moved segments.
Comments and suggestions are, of course, welcome,
regards,
vbr
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
# # # # # # # # # # # # # # # # # # # # #
#! Python
# -*- coding: utf-8 -*-
import difflib
import itertools
def compare_moves(a, b, similarity_threshold=0.6):
Poor man's text comparison with simple moves check. Compares two
strings using difflib
and additionally tries to detect moved blocks
by comparing similar deleted and inserted segments with each other
- given the similarity_threshold.
seq_matcher = difflib.SequenceMatcher(isjunk=None, a=a, b=b, autojunk=False)
diff_raw = [[tag, i1, i2, j1, j2, a[i1:i2], b[j1:j2]] for tag, i1,
i2, j1, j2 in seq_matcher.get_opcodes()]
deleted, inserted = {}, {}
for tag, i1, i2, j1, j2 in seq_matcher.get_opcodes():
if tag == 'delete':
deleted[(i1, i2)] = [tag, i1, i2, j1, j2, a[i1:i2]]
elif tag == 'insert':
inserted[(i1, i2)] = [tag, i1, i2, j1, j2, b[j1:j2]]
possibly_moved_blocks = []
for deleted_item, inserted_item in
itertools.product(deleted.values(), inserted.values()):
similarity_ratio = difflib.SequenceMatcher(isjunk=None,
a=deleted_item[5], b=inserted_item[5], autojunk=False).ratio()
if similarity_ratio = similarity_threshold:
possibly_moved_blocks.append([deleted_item, inserted_item,
similarity_ratio])
print diff_raw
print possibly_moved_blocks
if __name__ == __main__:
compare_moves(abcXYZdeABfghijklmnopABBCq,
ABCDabcdeACfgXYXZhijklmnopq, similarity_threshold = 0.6)
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
# # # # # #
# output: #
[['insert', 0, 0, 0, 4, '', 'ABCD'], ['equal', 0, 3, 4, 7, 'abc',
'abc'], ['delete', 3, 6, 7, 7, 'XYZ', ''], ['equal', 6, 9, 7, 10,
'deA', 'deA'], ['replace', 9, 10, 10, 11, 'B', 'C'], ['equal', 10, 12,
11, 13, 'fg', 'fg'], ['insert', 12, 12, 13, 17, '', 'XYXZ'], ['equal',
12, 21, 17, 26, 'hijklmnop', 'hijklmnop'], ['delete', 21, 25, 26, 26,
'ABBC', ''], ['equal', 25, 26, 26, 27, 'q', 'q']]
[[['delete', 21, 25, 26, 26, 'ABBC'], ['insert', 0, 0, 0, 4, 'ABCD'],
0.75], [['delete', 3, 6, 7, 7, 'XYZ'], ['insert', 12, 12, 13, 17,
'XYXZ'], 0.8571428571428571]]
compare_moves.py
Description: Binary data
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Re: Possible File iteration bug
On 7/15/2011 10:42 AM, Billy Mays wrote: On 07/15/2011 10:28 AM, Thomas Rachel wrote: Am 15.07.2011 14:52 schrieb Billy Mays: Really what would be useful is some sort of PauseIteration Exception which doesn't close the generator when raised, but indicates to the looping header that there is no more data for now. a None or other sentinel value would do this as well (as ChrisA already said). A sentinel does provide a work around, but it also passes the problem onto the caller rather than the callee: No more so than a new exception that the caller has to recognize. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
abort python script from trace function
Hello, I have a multithreaded application that uses embedded python extensively. The main thread creates python objects that interface test equipment, and users execute their own python scripts that run in a separate thread. The users need to be able to pause/resume/abort a script that is currently running. I registered a Py_tracefunc to check the state of the pause/abort buttons from the GUI, and pause/resume are working great. The trouble is that I cannot figure out how to implement an abort in my trace function. I can set exceptions use PyErr_SetString or PyThreadState_SetAsyncExc, but these just raise exceptions. If the script is in a block that defines a try/finally the exception will be caught, not what I want. In searching similar topics I saw references to PyErr_SetInterrupt, but this had no visible effect at all on my application. I don't want to call Py_Finalize and shut down the whole interpreter, because I would lose the Python objects created in the main thread. An uncatchable exception would be ideal. My embedded python version is: '2.6.5 (r265:79063, Mar 20 2010, 14:22:52) [MSC v.1500 32 bit (Intel)]' Thanks! -- http://mail.python.org/mailman/listinfo/python-list
Re: Looking for general advice on complex program
On 15Jul2011 16:03, Billy Mays 81282ed9a88799d21e77957df2d84bd6514d9...@myhashismyemail.com wrote: | I remember reading that file locking doesn't work on network mounted | drives (specifically nfs mounts), but you might be able to simply | create a 'lock' (mydoc.xml.lock or the like) file for the XML doc in | question. If that file exists you could either hang or silently | give up. Not sure if that helps. There are two approaches to this. Plain old make-a-file won't work - it is racy (and as mentioned, you can't rely on the various lock facilities). You can create a file while your umask is 0777; it will be non-writable immediately (no chmod required), preventing another attempt to make it. My personal habit is to make a directory for the lock; mkdir also can't happen twice to the same name, you don't need to fiddle you umask (racy and annoying, and problematic if you're using multiple threads), _and_ you can put meta info inside it, like pid files etc. Cheers, -- Cameron Simpson c...@zip.com.au DoD#743 http://www.cskk.ezoshosting.com/cs/ I had a wierd dream with Ken Thompson in it once. - George Politis geo...@research.canon.com.au -- http://mail.python.org/mailman/listinfo/python-list
Re: Python ++ Operator?
On Sat, Jul 16, 2011 at 6:26 AM, Dan Stromberg drsali...@gmail.com wrote: I don't regard this as a low level versus VHLL issue - I regard it as a matter of operators with side effects being too error prone. Adding such operators to Python has been discussed (it'd almost certainly be easy to add), and rejected. It's not that it has or has not, due to its highness of level, but more a needs or needs not. In Python, iterating over an array is done with a for loop and the array's own iterator (or enumerate() if you need the indices), but C doesn't have iterators, so it needs a convenient notation for incrementing through the array. BTW, array operations optimize to the same thing as pointer arithmetic in most C compilers, but the latter tends to be less clear. I'm not fully convinced; there are many times when incrementing pointers allows for much cleaner code. However, we are talking about the readability of C among Python programmers. Personally, I find pointer-dereference-and-post-increment to be perfectly readable, but it's a construct that I use practically on a daily basis. To someone who's not familiar with Python, list comps could suffer from the same issues - what does THIS do? oh. Chris Angelico -- http://mail.python.org/mailman/listinfo/python-list
Re: Proposal to extend PEP 257 (New Documentation String Spec)
On Sat, Jul 16, 2011 at 4:56 AM, rantingrick rantingr...@gmail.com wrote: Hmm, that's strange considering that code MUST be formatted in certain ways or you get a syntax error (indention, colons, parenthesis, etc, etc). I don't hear the masses claiming that they are going over to Ruby simply because of indention. Not Ruby, but to other languages. There's this guy in my house named Chris who tries his best to avoid Python if the code is going to be shared over any dodgy medium where indentation might be damaged. There are plenty of other languages that he can use... oh wait, that's me. Yes, I frequently avoid Python specifically because of its indentation issues. Does that mean I never use Python? No. Does it mean I don't post here? Obviously not. Does it mean that further restrictions can automatically be grandfathered in because there are already restrictions like this? No. In my mind doc-strings should ALWAYS be optional HOWEVER if the programmer decides to create a doc-string THEN he must observe some syntax rules or his code will throw an SyntaxError. Remember, freedom is good, unbridled freedom is the root of all evil. 1) Every syntax element MUST add indentation. 2) Strong encouragement to stick to an 80-character line Conclusion: Every big function will become two smaller functions, one of which calls the other. 3) Every function that has a docstring MUST have it fully formatted. Secondary conclusion: The only functions with docstrings are the ones that are meant to be called externally. In other words, docstrings will define the module's interface, and there'll be a whole lot of utterly undocumented functions because they didn't merit this massive structured docstring, and it became way way too much work to factor things out. Either that, or people will just start ignoring the 80 character limit, but I'm sure you could make that mandatory - and that one would actually improve some things, because any program that wants to read Python code needs only allocate an 81-character buffer. So what's so terrible about structure Chris? Nobody's freedom are being taken away. You don't HAVE to create doc-strings, just like you don't HAVE to code with Python (you do free form formatting Ruby). Python is a language that is meant to be clean. Forced indention makes that possible. Forced doc-string syntax will complete the circle. Python was also meant to be a programming language. Programming languages offer freedom to their users. Without that freedom, it's not a programming language but a script for another program... such things can be useful, but are not the same. This is not a true programming language: http://www.kongregate.com/games/Coolio_Niato/light-bot It's a reasonably fun game, but specifically _because_ it's so restrictive. That is NOT what I want from a programming language or even a scripting language. Chris Angelico -- http://mail.python.org/mailman/listinfo/python-list
Is there a Programming FAQ for Python 3.x?
Is there a Programming FAQ for Python 3.x? There is http://docs.python.org/faq/programming.html, but it's for 2.7 Thanks, Dick Moores -- http://mail.python.org/mailman/listinfo/python-list
Type checking versus polymorphism (was: list(), tuple() should not place at Built-in functions in documentation)
Inside fancheyuj...@gmail.com writes: I just follow some coding rules of me: 1. Controlling input strictly. Asserting that the input is of a specific type is too strict. Does your code work if the input is not a list or tuple? I suspect strongly that the answer is yes, it works fine with any sequence, even ones that don't inherit from ‘list’ nor ‘tuple’. It will probably work with any sequence; it amy even work with any iterable. Instead of insisting on specific types, you should support polymorphism: expect *behaviour* and allow any input that exhibits that behaviour. This is known as “duck typing”: you don't need to care whether it's a duck, you just need to know whether it walks like a duck and quacks like a duck. If it turns out to be a goose, but that won't affect your code, you shouldn't care. 2. In a function keep doubting on its parameters until they're checked. This is called “Look Before You Leap” (LBYL) programming, and is generally considered not Pythonic. Rather, “it is Easier to Ask Forgiveness than Permission” (EAFP) is the Python programming style, and fits with its widespread reliance on polymorphism (including “duck typing”). Accept the input, and use it as though it has the correct behaviour – without regard to what type is providing that behaviour. If it doesn't have the expected behaviour, either the type will complain (raising an exception that you can handle at an appropriate level in your code), or your comprehensive unit tests will detect the misbehaviour. If you don't have comprehensive unit tests, that's where you should put your effort of strict interface testing. Not type assertions in the application code. 3. Let potential errors raise as early as possible. That is good practice. But you should not compromise polymorphism to that. -- \“The whole area of [treating source code as intellectual | `\property] is almost assuring a customer that you are not going | _o__) to do any innovation in the future.” —Gary Barnett | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: list(), tuple() should not place at Built-in functions in documentation
On Sat, Jul 16, 2011 at 5:53 AM, Inside fancheyuj...@gmail.com wrote: def add(users): assert(users, (tuple, list)) #If necessary I'll also check every obj in the sequence to see whether it's a User. I just follow some coding rules of me: 1. Controlling input strictly. 2. In a function keep doubting on its parameters until they're checked. 3. Let potential errors raise as early as possible. What you're doing there is writing code in Python, not writing Python code. To be more Pythonic, your code should actually stop caring about whether something is-a User, and instead simply care about whether or not it can be treated as a User. (And for Travaglia fans, yes, a User object WILL have an abuse() method.) Instead of asserting that the parameter is a User, just add it cheerfully to your list, and then when you iterate over the list and call some method on each one, you'll get an exception if one of them doesn't have that method. This allows a huge enhancement to polymorphism, in that you no longer need to worry about what your pointers are; in C++, you can run over a list of users and ask if they're all Students, but then you need to cast all those pointers if you're going to then ask them all what subjects they're studying. In Python, all you do is ask your list of objects what subjects they're studying - all the students will respond, and anything that doesn't know what studying is will throw an exception. The analogy with reality breaks down a bit here. I've seen plenty of students with no idea of what it means to study. But Python can handle that too - just 'del' the method in the subclass. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Python threading/multiprocessing issue.
2011/7/16 Lee Harr miss...@hotmail.com: I am not a multiprocessing expert, but I think the problem you are having is that Process is running your code in a separate process, so there is no way you could see those object changes in your main line code. In other words, Process is not an exact replacement for Thread. That's correct; inter-process communication is the realm of sockets (network or Unix), pipes, signals, etc - but inter-thread communication is a matter of making sure you don't tread on each other's toes. In CPython, the latter is guaranteed by the GIL; the specific advantage of multiprocessing over threading is that each process has a separate GIL, and that's because all variables are separate. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Is there a Programming FAQ for Python 3.x?
On 07/16/2011 01:24 AM, Richard D. Moores wrote: Is there a Programming FAQ for Python 3.x? There is http://docs.python.org/faq/programming.html, but it's for 2.7 Thanks, Dick Moores http://docs.python.org/py3k/faq/index.html http://docs.python.org/py3k/faq/programming.html -- http://mail.python.org/mailman/listinfo/python-list
Re: abort python script from trace function
On Sat, Jul 16, 2011 at 8:00 AM, Dave Stark david.st...@intusurg.com wrote: Hello, I have a multithreaded application that uses embedded python extensively. The main thread creates python objects that interface test equipment, and users execute their own python scripts that run in a separate thread. I did something extremely similar (but without the threading), and was majorly burnt. Poke around on the archives and you'll find the extent to which I (and my boss) got egg on our faces; I had thought that it would be possible to sandbox Python enough for a user to be able to submit code. It's not. If you're fortunate, someone from this list will create a file in /tmp, read it back, and then email you showing how easy it was to do. If you're not, it'll be utter and complete p0wnage. PyErr_SetInterrupt() raises KeyboardInterrupt. It works fine, as long as the script catches that. I had the same issues with my system; I wanted to administratively guarantee that the script WOULD NOT take more than X ms of CPU time. Since a Python script can catch KeyboardInterrupt, it could ignore the watchdog timer. In the end, I created a second watchdog that, if triggered, would longjmp straight out past all the Python code and back to a basic cleanup-and-terminate routine. There's no way, currently, to make an uncatchable exception. I already asked. The general response is (and I should have listened, instead of muffling on and hoping that we could sandbox Python enough to get by) that Python is not the right language for that sort of job. I was advised to try Javascript/ECMAScript, and Google's V8 engine is fairly good; not perfect, but decent. Alternatively, Lua works well, but it's a lot more effort to embed (especially if you want heavy interfacing between the script code and your application code - everything's done with a stack). Chris Angelico -- http://mail.python.org/mailman/listinfo/python-list
Re: Is there a Programming FAQ for Python 3.x?
On Fri, Jul 15, 2011 at 16:39, Thomas Jollans t...@jollybox.de wrote: On 07/16/2011 01:24 AM, Richard D. Moores wrote: Is there a Programming FAQ for Python 3.x? There is http://docs.python.org/faq/programming.html, but it's for 2.7 Thanks, Dick Moores http://docs.python.org/py3k/faq/index.html Excellent! I was going from http://docs.python.org/py3k/index.html where I chose FAQs from the left column. Dick -- http://mail.python.org/mailman/listinfo/python-list
Re: Looking for general advice on complex program
On Sat, Jul 16, 2011 at 8:37 AM, Cameron Simpson c...@zip.com.au wrote: There are two approaches to this. You can create a file while your umask is 0777... [or] My personal habit is to make a directory for the lock Both viable options; I'd be inclined toward the second. Or, here's a third option. Instead of writing to a shared network drive, submit requests on a TCP socket direct to the monitor program. Spin off a thread that does this: * Wait for incoming socket connection * Set overall cutoff timer; if (say) 2 seconds pass, kill the connection * Authenticate the client (if applicable) * Accept the update data, sanitize if necessary * Write the file to disk * Notify the XManager * Loop. Do all this on *one thread* and then you eliminate all race conditions. Good use of a TCP listen queue and the cutoff timer will mean that applications aren't actually kept waiting, but they're still rigidly locked into a queue - depending on how frequent your updates are, this could be a problem. If you need simultaneous updates, spin off a new thread for each socket connection, and then use something simple like a mapping of file name to semaphore to ensure no two try to update the same file at once. By moving the actual file read/writes to a single computer, you simplify the task of notifying the parent. In fact, if there's only one process that needs to be made aware of the change, the job's even easier - all you need to do is change a variable or call a method or whatever it be, right there in the socket handler. Chris Angelico -- http://mail.python.org/mailman/listinfo/python-list
Print encoding problems in console
Hello everyone. I'm having a problem when outputing UTF-8 strings to a console. Let me show a simple example that explains it: $ python -c 'import sys; print sys.stdout.encoding; print u\xe9' UTF-8 é It's everything ok. Now, if you're using your python script in some shell script you might have to store the output in some variable, like this: $ var=`python -c 'import sys; print sys.stdout.encoding; print u\xe9'` And what you get is: Traceback (most recent call last): File string, line 1, in module UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in position 0: ordinal not in range(128) So, python is not being able to detect the encoding of the output in a situation like that, in which the python script is called not directly but around ``. Why does happen? Is there a way to solve it either by python or by shell code? Thanks, Pedro Abranches -- http://mail.python.org/mailman/listinfo/python-list
Liskov substitution principle (was: list(), tuple() should not place at Built-in functions in documentation)
Chris Angelico ros...@gmail.com writes: The analogy with reality breaks down a bit here. I've seen plenty of students with no idea of what it means to study. But Python can handle that too - just 'del' the method in the subclass. No, please don't. That would break the Liskov substitution principle URL:https://secure.wikimedia.org/wikipedia/en/wiki/Liskov_substitution_principle. By inheriting from a type that provides a method, you're promising that you will implement at least as much behaviour as the parent. If that includes a ‘study’ method, then your subclass must also implement (or inherit) that method. Code can then be written to expect that, so long as the object inherits from Student, it will at least have the same minimum level of behaviour that a Student has. If you inherit from Student, but delete the ‘study’ method, you would break any code which assumes any Student has a ‘study’ method – something that was explicitly promised in the API of Student. Since you are advocating calling people students when they don't study, it sounds instead like you want a different set of promises: class Student(Person): An enrolled student at this institution. def study(self, subject): raise NotImplementedError class LectureAttendee(Student): Someone who comes to lectures. def attend(self, lecture): pass class StudentWhoActuallyStudies(Student): A student who actually is capable of studying. def study(self, subject): Actually apply my knowledge of how to study. alice = StudentWhoActuallyStudies(Alice) bob = Student(Bob) alice.study(chemistry) # actual study bob.study(garden gnome painting) # not implemented! Now both Alice and Bob fulfil the technical requirements of a student at the institution, but the expectations of study capability are clear. Any code using this implementation of Student knows that, if they want a student who actually studies, they'd better ask for a more specific type. See? We can have overstretched analogies *and* remain within the Liskov substitution principle. -- \ Eccles: “I just saw the Earth through the clouds!” Lew: “Did | `\ it look round?” Eccles: “Yes, but I don't think it saw me.” | _o__)—The Goon Show, _Wings Over Dagenham_ | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Liskov substitution principle (was: list(), tuple() should not place at Built-in functions in documentation)
On Sat, Jul 16, 2011 at 10:04 AM, Ben Finney ben+pyt...@benfinney.id.au wrote: def study(self, subject): raise NotImplementedError See? We can have overstretched analogies *and* remain within the Liskov substitution principle. Hehe! Of course I was speaking utterly in jest, but this raises (sorry, never could resist a bad pun) another question: What if the base class implemented study(), and then LazyStudent subclasses Student but makes study() raise NotImpl? Would that break things? In a sense, it breaks the whole this is a student so it should act like a student rule. Suppose it raised UtterApathyError instead - does that break the LSP? Chris A PS. The world's first horseless signature... trapped in the air! -- http://mail.python.org/mailman/listinfo/python-list
Re: Print encoding problems in console
I've used the code below successfully to deal with such a problem when
outputting filenames. Python2x3 is at
http://stromberg.dnsalias.org/svn/python2x3/ , but here it's just being used
to convert Python 3.x's byte strings to strings (to eliminate the b''
stuff), while on 2.x it's an identity function - if you're targeting 3.x
alone, there's no need to take a dependency on python2x3.
If you really do need to output such characters, rather than replacing them
with ?'s, you could use os.write() to filedescriptor 1 - that works in both
2.x and 3.x.
def ascii_ize(binary):
'''Replace non-ASCII characters with question marks; otherwise writing to
sys.stdout tracebacks'''
list_ = []
question_mark_ordinal = ord('?')
for ordinal in python2x3.binary_to_intlist(binary):
if 0 = ordinal = 127:
list_.append(ordinal)
else:
list_.append(question_mark_ordinal)
return python2x3.intlist_to_binary(list_)
def output_filename(filename, add_eol=True):
'''Output a filename to the tty (stdout), taking into account that some
tty's do not allow non-ASCII characters'''
if sys.stdout.encoding == 'US-ASCII':
converted = python2x3.binary_to_string(ascii_ize(filename))
else:
converted = python2x3.binary_to_string(filename)
replaced = converted.replace('\n', '?').replace('\r', '?').replace('\t',
'?')
sys.stdout.write(replaced)
if add_eol:
sys.stdout.write('\n')
On Fri, Jul 15, 2011 at 5:02 PM, Pedro Abranches pedrof.abranc...@gmail.com
wrote:
Hello everyone.
I'm having a problem when outputing UTF-8 strings to a console.
Let me show a simple example that explains it:
$ python -c 'import sys; print sys.stdout.encoding; print u\xe9'
UTF-8
é
It's everything ok.
Now, if you're using your python script in some shell script you might have
to store the output in some variable, like this:
$ var=`python -c 'import sys; print sys.stdout.encoding; print u\xe9'`
And what you get is:
Traceback (most recent call last):
File string, line 1, in module
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in
position 0: ordinal not in range(128)
So, python is not being able to detect the encoding of the output in a
situation like that, in which the python script is called not directly but
around ``.
Why does happen? Is there a way to solve it either by python or by shell
code?
Thanks,
Pedro Abranches
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Re: Print encoding problems in console
-BEGIN PGP SIGNED MESSAGE-
Hash: RIPEMD160
On 2011.07.15 07:02 PM, Pedro Abranches wrote:
Now, if you're using your python script in some shell script you
might have to store the output in some variable, like this:
$ var=`python -c 'import sys; print sys.stdout.encoding; print
u\xe9'`
And what you get is:
Traceback (most recent call last): File string, line 1, in
module UnicodeEncodeError: 'ascii' codec can't encode character
u'\xe9' in position 0: ordinal not in range(128)
So, python is not being able to detect the encoding of the output in
a situation like that, in which the python script is called not
directly but around ``.
FWIW, it works for me with Python 3:
$ x=$(/c/Python32/python -c print\(\'\\xe9\'\))
$ echo $x
é
I don't know how to get it to work with more than one command to Python;
bash always thinks the next commands are for it:
$ x=$(/c/Python32/python -c import sys; print\(sys.output.encoding\);
print\(\'\\xe9\'\))
File string, line 1
import
^
SyntaxError: invalid syntax
bash: print(sys.output.encoding): command not found
bash: print('\xe9'): No such file or directory
This is using a very old MinGW bash, though.
- --
CPython 3.2.1 | Windows NT 6.1.7601.17592 | Thunderbird 5.0
PGP/GPG Public Key ID: 0xF88E034060A78FCB
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Re: Liskov substitution principle
Chris Angelico ros...@gmail.com writes: What if the base class implemented study(), and then LazyStudent subclasses Student but makes study() raise NotImpl? Would that break things? In a sense, it breaks the whole this is a student so it should act like a student rule. That would break the Liskov substitution principle, yes. Anything that asks for a Student instance should receive an object that can do at least everything Student can do. If you want to implement something that can't do some of the things Student can do, the Liskov substitution principle says you are implementing some object that does *not* inherit from Student. This fits nicely with the principle (whose name I'm currently too lazy to look up) that says you should only use inheritance for “IS-A” relationships. If LazyStudent can't do everything Student can do, then it's false to say LazyStudent IS-A Student, so using inheritance for that would be to state something in code which isn't true. Suppose it raised UtterApathyError instead - does that break the LSP? Probably, yes. Your point is taken though: it's not something that can be drawn along a bright line. -- \ “Those are my principles. If you don't like them I have | `\others.” —Groucho Marx | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: None versus MISSING sentinel -- request for design feedback
Ethan Furman wrote: some of the return values (Logical, Date, DateTime, and probably Character) will have their own dedicated singletons (Null, NullDate, NullDateTime, NullChar -- which will all compare equal to None) That doesn't seem like a good idea to me. It's common practice to use 'is' rather than '==' when comparing things to None. Why do you want to use special null values for these types? -- Greg -- http://mail.python.org/mailman/listinfo/python-list
Re: Type checking versus polymorphism (was: list(), tuple() should not place at Built-in functions in documentation)
Ben Finney wrote: [...snip explanation of duck-typing...] If you don't have comprehensive unit tests, that's where you should put your effort of strict interface testing. Not type assertions in the application code. I agree with everything Ben said here, but he has missed something even more fundamental. Type *checking* breaks duck-typing. Type *assertions* are even worse, because assertions aren't guaranteed to run. If you are using assert isinstance(...) to validate input data, there are situations where your validation step does not happen at all, and your code may just break in the least convenient way. So not only are you validating the wrong way, but sometimes you don't validate at all! Assertions are for testing internal program logic, not for validation. (I don't even like using assert for testing. How do you test your code with assertions turned off if you use assert for testing?) -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
Billy Mays wrote: I was thinking that a convenient solution to this problem would be to introduce a new Exception call PauseIteration, which would signal to the caller that there is no more data for now, but not to close down the generator entirely. It never fails to amuse me how often people consider it convenient to add new built-in functionality to Python to solve every little issue. As pie-in-the-sky wishful-thinking, it can be fun, but people often mean it to be taken seriously. Okay, we've come up with the solution of a new exception, PauseIteration, that the iterator protocol will recognise. Now we have to: - write a PEP for it, setting out the case for it; - convince the majority of CPython developers that the idea is a good one, which might mean writing a proof-of-concept version; - avoid having the Jython, IronPython and PyPy developers come back and say that it is impossible under their implementations; - avoid having Guido veto it; - write an implementation or patch adding that functionality; - try to ensure it doesn't cause any regressions in the CPython tests; - fix the regressions that do occur despite our best efforts; - ensure that there are no backwards compatibility issues to be dealt with; - write a test suite for it; - write documentation for it; - unless we're some of the most senior Python developers, have the patch reviewed before it is accepted; - fix the bugs that have come to light since the first version; - make sure copyright is assigned to the Python Software Foundation; - wait anything up to a couple of years for the latest version of Python, including the patch, to be released as production-ready software; - upgrade our own Python installation to use the latest version, if we can and aren't forced to stick with an older version and now, at long last, we can use this convenient feature in our own code! Pretty convenient, yes? (If you think I exaggerate, consider the yield from construct, which has Guido's support and was pretty uncontroversial. Two and a half years later, it is now on track to be added to Python 3.3.) Or you can look at the various recipes on the Internet for writing tail-like file viewers in Python, and solve the problem the boring old fashioned way. Here's one that blocks while the file is unchanged: http://lethain.com/tailing-in-python/ Modifying it to be non-blocking should be pretty straightforward -- just add a `yield ` after the `if not line`. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Possible File iteration bug
On Sat, Jul 16, 2011 at 1:42 PM, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: Okay, we've come up with the solution of a new exception, PauseIteration, that the iterator protocol will recognise. Now we have to: - write an implementation or patch adding that functionality; - and add it to our own personal builds of Python, thus bypassing the entire issue of getting it accepted into Python. Of course, this does mean that your brilliant code only works on your particular build of Python, but I'd say that this is the first step - before writing up the PEP, run it yourself and see whether you even like the way it feels. THEN, once you've convinced yourself, start convincing others (ie PEP). ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: list(), tuple() should not place at Built-in functions in documentation
Inside wrote: Why I use assertion,please check this code: class User(object):pass class Student(User):pass class Professional(User):pass def add(user): assert(user, User) This does not do what you think it does. All it does is, in some Python versions, print SyntaxWarning: assertion is always true, perhaps remove parentheses? In other Python versions, it is a no-op: it does nothing. Perhaps you meant this? assert isinstance(user, User) Ben has already posted why isinstance type-checking should usually be avoided in favour of duck-typing (if it looks like a duck, and sounds like a duck, and swims like a duck, it might as well be a duck). But let's suppose you have good reason for sticking to an explicit type-check. The problem now is with the assert! Assertions are not guaranteed to run. The caller can turn them off by running Python with the -O (optimize) switch. Another problem: AssertionError is the wrong sort of exception to raise on bad arguments. It should normally be TypeError or ValueError, or some other more specific exception, with a useful error message. Assertions are for testing your own program logic, not for validating input. For example, in one of my own libraries, I have this piece of code: data = _countiter(data) assert data.count == 0 total = sum(data) n = data.count assert n = 0 # much later on... return math.sqrt(value/n) _countiter is a wrapper that keeps track of how many items have been iterated over. I take an arbitrary iterator, wrap it, sum the values, then check that the number of items is not a negative number. If it is, that's a bug in my program logic, and I should find out as soon as possible, not much later on when I try to take the square root of it. Assertions should be rare, and never used for testing arguments (except, maybe, for purely internal functions that only get called by your own functions, never by the caller). If the caller ever sees an AssertionError generated by your code, that is a bug in your code. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: An interesting beginner question: why we need colon at all in the python language?
Wanderer wrote: But if you have the colon, why do you need the brackets or backslashes in an if statement. Why not if condition1 or condition2 or condition3: do_something() The statement ain't over til there's a colon. Because there are virtues in having the parser be nice and simple. Syntax constraints help identify errors: mystr = this is a string Should we say that no closing quote is needed, because the newline unambiguously ends the string? Well, perhaps... but allowing such a rule would mask errors: mystr = this is a %s % type(something) Good language design requires constraints on what is allowed as well as freedom from unnecessary syntax. The appropriate lines from the Zen are Errors should never pass silently. Unless explicitly silenced. Newlines end parsing of the current token or expression. Including a newline inside an expression is an error, unless you explicitly silence it by using a backslash or using brackets. It's a bit too far to say that any if statement is an explicit way to silent newline errors. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: HOWTO: Parsing email using Python part2
aspineux wrote: Hello I have written part 2 about parsing email. You can find the article here : http://blog.magiksys.net/parsing-email-using-python-content This part is a lot longer : Wow! Well done. Thank you for sharing this, this is extremely detailed and useful. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Type checking versus polymorphism (was: list(), tuple() should not place at Built-in functions in documentation)
On Fri, Jul 15, 2011 at 7:47 PM, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: snip Assertions are for testing internal program logic, not for validation. (I don't even like using assert for testing. How do you test your code with assertions turned off if you use assert for testing?) I would think that would only matter if either the asserted expressions caused side-effects or there was nontrivial logic in the AssertionError handler, which would indicate a rather screwy codebase and point to a possible PEBKAC issue that testing cannot hope to remedy. Cheers, Chris -- http://rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Python threading/multiprocessing issue.
On Sat, Jul 16, 2011 at 3:15 PM, Dennis Lee Bieber wlfr...@ix.netcom.com wrote: And (so far as I understand it) each process can claim its own CPU core, whereas threads share the active core. Threads can be put onto separate cores too, and can have their affinities set. But because of the GIL, actual CPython code can't run on two cores at once. You might be able to have two Python threads running at once if they're calling into C modules most of the time, but it's much safer to either go multiprocessing or to use I/O bound threads (eg socket handlers). ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: list(), tuple() should not place at Built-in functions in documentation
Perhaps you meant this? assert isinstance(user, User) Yes I meant this,sorry,my mistake. Thx for your and Ben's feedbacks first,it's appreciated. your points is taken by me,but I want to make my opinion more clearly. The assertion is JUST show to my function callers during development,warning that I want a list/tuple,not some other objects(BTW, your practice of wrapping arguments to iter is good,I'll take this to improve my code,thx again.).And assertion's off when running Python with the -O (optimize) switch is what I expect,it isn't necessary in production code.Argument validation is done by constuctor of object which I used in assertion. I also have a few words about duck-typing.Duck-typing is good,but how about if I offer a convenient way to my function user by producing or changing what he want to pass me to a *real* duck?Is that more explicit to my user? Anyway,I'll look at my principles which may need some changes or improvements. -- http://mail.python.org/mailman/listinfo/python-list
Re: Questions about os.waitpid(pid, options) on windows
On Mon, 11 Jul 2011 20:59:29 -0700 (PDT) Fan zjuwu...@gmail.com wrote: It seems that waitpid take process handle instead of process id as the first parameter on Windows. On Unices platform, the first parameter is process id. This interface is a little bit confusing. What's the purpose for such a design? Thanks a lot, Fan I would assume it's because that's how the underlying OS primitives work. Under Windows, concepts of process ID and process handle both exist (and are separate), and the functions that wait for events to occur (WaitForSingleObject, WaitForMultipleObjects, and so on) take handles of various sorts, including process handles. Under Linux, there is no such thing as a process handle, only a process ID, and waitpid (the system call) takes a process ID. Chris -- http://mail.python.org/mailman/listinfo/python-list
MemoryError vs malloc error
Hi, I've a long running python process (running on freebsd). Sometimes when it uses too much memory it core dumps. I would've expected it to raise MemoryError. Normally, when would a python process raise MemoryError and when would it fail with malloc error and cores? This is happening in pure python code (Eg. if ' '.join(biglist)) etc. Regards, Amit -- http://mail.python.org/mailman/listinfo/python-list
