I think it would be a good idea if Python tracebacks could be translated
into languages other than English - and it would set a good example.
For example, using French as my default local language, instead of
>>> 1/0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: integer division or modulo by zero
I might get something like
>>> 1/0
Suivi d'erreur (appel le plus récent en dernier) :
Fichier "<stdin>", à la ligne 1, dans <module>
ZeroDivisionError: division entière ou modulo par zéro
André
Here's an updated version of the PEP reflecting my
recent suggestions on how to eliminate 'codef'.
PEP: XXX
Title: Cofunctions
Version: $Revision$
Last-Modified: $Date$
Author: Gregory Ewing <greg.ewing(a)canterbury.ac.nz>
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 13-Feb-2009
Python-Version: 3.x
Post-History:
Abstract
========
A syntax is proposed for defining and calling a special type of generator
called a 'cofunction'. It is designed to provide a streamlined way of
writing generator-based coroutines, and allow the early detection of
certain kinds of error that are easily made when writing such code, which
otherwise tend to cause hard-to-diagnose symptoms.
This proposal builds on the 'yield from' mechanism described in PEP 380,
and describes some of the semantics of cofunctions in terms of it. However,
it would be possible to define and implement cofunctions independently of
PEP 380 if so desired.
Specification
=============
Cofunction definitions
----------------------
A cofunction is a special kind of generator, distinguished by the presence
of the keyword ``cocall`` (defined below) at least once in its body. It may
also contain ``yield`` and/or ``yield from`` expressions, which behave as
they do in other generators.
From the outside, the distinguishing feature of a cofunction is that it cannot
be called the same way as an ordinary function. An exception is raised if an
ordinary call to a cofunction is attempted.
Cocalls
-------
Calls from one cofunction to another are made by marking the call with
a new keyword ``cocall``. The expression
::
cocall f(*args, **kwds)
is evaluated by first checking whether the object ``f`` implements
a ``__cocall__`` method. If it does, the cocall expression is
equivalent to
::
yield from f.__cocall__(*args, **kwds)
except that the object returned by __cocall__ is expected to be an
iterator, so the step of calling iter() on it is skipped.
If ``f`` does not have a ``__cocall__`` method, or the ``__cocall__``
method returns ``NotImplemented``, then the cocall expression is
treated as an ordinary call, and the ``__call__`` method of ``f``
is invoked.
Objects which implement __cocall__ are expected to return an object
obeying the iterator protocol. Cofunctions respond to __cocall__ the
same way as ordinary generator functions respond to __call__, i.e. by
returning a generator-iterator.
Certain objects that wrap other callable objects, notably bound methods,
will be given __cocall__ implementations that delegate to the underlying
object.
Grammar
-------
The full syntax of a cocall expression is described by the following
grammar lines:
::
atom: cocall | <existing alternatives for atom>
cocall: 'cocall' atom cotrailer* '(' [arglist] ')'
cotrailer: '[' subscriptlist ']' | '.' NAME
Note that this syntax allows cocalls to methods and elements of sequences
or mappings to be expressed naturally. For example, the following are valid:
::
y = cocall self.foo(x)
y = cocall funcdict[key](x)
y = cocall a.b.c[i].d(x)
Also note that the final calling parentheses are mandatory, so that for example
the following is invalid syntax:
::
y = cocall f # INVALID
New builtins, attributes and C API functions
--------------------------------------------
To facilitate interfacing cofunctions with non-coroutine code, there will
be a built-in function ``costart`` whose definition is equivalent to
::
def costart(obj, *args, **kwds):
try:
m = obj.__cocall__
except AttributeError:
result = NotImplemented
else:
result = m(*args, **kwds)
if result is NotImplemented:
raise TypeError("Object does not support cocall")
return result
There will also be a corresponding C API function
::
PyObject *PyObject_CoCall(PyObject *obj, PyObject *args, PyObject *kwds)
It is left unspecified for now whether a cofunction is a distinct type
of object or, like a generator function, is simply a specially-marked
function instance. If the latter, a read-only boolean attribute
``__iscofunction__`` should be provided to allow testing whether a given
function object is a cofunction.
Motivation and Rationale
========================
The ``yield from`` syntax is reasonably self-explanatory when used for the
purpose of delegating part of the work of a generator to another function. It
can also be used to good effect in the implementation of generator-based
coroutines, but it reads somewhat awkwardly when used for that purpose, and
tends to obscure the true intent of the code.
Furthermore, using generators as coroutines is somewhat error-prone. If one
forgets to use ``yield from`` when it should have been used, or uses it when it
shouldn't have, the symptoms that result can be extremely obscure and confusing.
Finally, sometimes there is a need for a function to be a coroutine even though
it does not yield anything, and in these cases it is necessary to resort to
kludges such as ``if 0: yield`` to force it to be a generator.
The ``cocall`` construct address the first issue by making the syntax directly
reflect the intent, that is, that the function being called forms part of a
coroutine.
The second issue is addressed by making it impossible to mix coroutine and
non-coroutine code in ways that don't make sense. If the rules are violated, an
exception is raised that points out exactly what and where the problem is.
Lastly, the need for dummy yields is eliminated by making it possible for a
cofunction to call both cofunctions and ordinary functions with the same syntax,
so that an ordinary function can be used in place of a cofunction that yields
zero times.
Record of Discussion
====================
An earlier version of this proposal required a special keyword ``codef`` to be
used in place of ``def`` when defining a cofunction, and disallowed calling an
ordinary function using ``cocall``. However, it became evident that these
features were not necessary, and the ``codef`` keyword was dropped in the
interests of minimising the number of new keywords required.
The use of a decorator instead of ``codef`` was also suggested, but the current
proposal makes this unnecessary as well.
It has been questioned whether some combination of decorators and functions
could be used instead of a dedicated ``cocall`` syntax. While this might be
possible, to achieve equivalent error-detecting power it would be necessary
to write cofunction calls as something like
::
yield from cocall(f)(args)
making them even more verbose and inelegant than an unadorned ``yield from``.
It is also not clear whether it is possible to achieve all of the benefits of
the cocall syntax using this kind of approach.
Prototype Implementation
========================
An implementation of an earlier version of this proposal in the form of patches
to Python 3.1.2 can be found here:
http://www.cosc.canterbury.ac.nz/greg.ewing/python/generators/cofunctions...
If this version of the proposal is received favourably, the implementation will
be updated to match.
Copyright
=========
This document has been placed in the public domain.
..
Local Variables:
mode: indented-text
indent-tabs-mode: nil
sentence-end-double-space: t
fill-column: 70
coding: utf-8
End:
Hello,
Python 3 has removed callable() under the justification that's it's not
very useful and duck typing (EAFP) should be used instead. However,
it has since been felt by many people that it was an annoying loss;
there are situations where you truly want to know whether something is a
callable without actually calling it (for example when writing
sophisticated decorators, or simply when you want to inform the user
of an API misuse).
The substitute of writing `isinstance(x, collections.Callable)` is
not good, 1) because it's wordier 2) because collections is really not
an intuitive place where to look for a Callable ABC.
So, I would advocate bringing back the callable() builtin, which was
easy to use, helpful and semantically sane.
Regards
Antoine.
On Mon, Jan 31, 2011 at 7:17 PM, Jurjen N.E. Bos
<j.bos-interpay(a)xs4all.nl> wrote:
> Did anyone try this already? If not, I might take up the gauntlet
> and try it myself, but I never did this before...
a) This is more on topic for python-ideas rather than python-dev (cc
changed accordingly)
b) My off-the-top-of-my-head guess is that caching effects will swamp
any impact such a change might have. The only way to find out for sure
is going to be for someone to try it (along the lines of the already
mentioned WPython variant) and see what happens for benchmarks like
pybench and the execution times of various test suites.
Cheers,
Nick.
--
Nick Coghlan | ncoghlan(a)gmail.com | Brisbane, Australia
We have a threading.Timer class which executes after a given delay and then
terminates. I was thinking about a pre-made class that would execute, wait
an interval, and then repeat. It would cut down on the logic people need to
implement themselves, and make simple scripts faster.
Here are some use cases:
# Send a ping message to all connected clients every 120 seconds
from server import ping_all_clients
pinger = threading.RepeatTimer(120, ping_all_clients)
pinger.start()
# Check for updates every 3 hours
from mymodule import check_for_updates
update_checker = threading.RepeatTimer(60*60*3, check_for_updates)
update_checker.start()
I was thinking of the class having an initializer signature as follows:
class threading.RepeatTimer(interval, function, args=[], kwargs={},
limit=None)
Create a timer that will run function with args and kwargs and repeat
every interval secods. If limit is
an integer, limits repetitions to that many calls.
cancel()
Stop the repeat timer. If in the middle of a call, the call is
allowed to finish.
Daniel
Moving these suggestions to python ideas as they are not immediately
relevant to the current python dev discussion at this time. ;-)
I'm really just wondering what others think, is this something worth
working on?
On 01/24/2011 01:46 PM, Raymond Hettinger wrote:
> Right now, the tests for the unittest package are under the package
> directory instead of Lib/test where we have most of the other tests.
>
> There are some other packages that do the same thing, each for their own
> reason.
>
> I think we should develop a strong preference for tests going under
> Lib/test unless there is a very compelling reason.
> * For regrtest to work, there still needs to be some file in Lib/test
> that dispatches to the alternate test directory.
Currently tests are mostly separate from the modules. Mostly separate
because, some modules have doctests in them, and/or a test() function to
run tests. But the test function name isn't special in any way as far as I
know. It's usually _test(), but it could be something else.
Would it help things to have a special __test__ name? ie... special to
python, in that module.__test__() can be depended on to run the tests for
that module? (or package)
I've found it useful to add a -T option to my own python applications to
run tests. But moving it from being a module option to a python option,
would make that even nicer. Where python -T modulename called the
__test__() function. (or evoke the tests in another way.)
With a dependable way to evoke the tests no matter where they are located,
it then becomes just a matter of iterating the list of modules in the
library (or a directory) to run all the tests.
But then, what's the best way to actually do that?
The current method uses pattern matching ... (not my first choice for sure)
python -m unittest discover -s project_directory -p '*_test.py'
python -m unittest discover project_directory '*_test.py'
Those lines are way too long in my opinion.
In the above, the test functions need to begin with an underscore. I'm not
sure the discoverable test function should be private, The very act of
finding them suggests they should be a public, but special API, rather than
a private API to me. If they were only accessed from inside the module or
package they are in, then being private makes sense.
One choice is that __test__ is special to doctest and unittest only.
python -m unittest module # runs module.__test__() if it exists.
Or a little more far out ...
The __test__() function could be called with "python -T module". But then
it seems that maybe we could also have a __main__() function be called with
"python -M module". (?)
Alternately ... "python -T module" could alter the name of the module.
if __name__ == "__main__":
main()
elif __name__ == "__test__":
_test() # a private name is ok here.
Cheers,
Ron
Hey, guys
I must argue that make **kwargs sorted is really a terrible idea.
Please think that when user wants a unsorted **kwargs, how can he or she
bring the original unsorted dict back?
When a dict is unsorted, we can sort it with implementation in Python/C
interface or just python code for portability. That is what should be like!
Give users more control over behavior of dict. That is what I propose.
Best regards
Hongbao Chen
XJTU
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发送时间: 2011年1月21日 1:52
收件人: python-ideas(a)python.org
主题: Python-ideas Digest, Vol 50, Issue 34
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Today's Topics:
1. Re: A sorted version of **kwargs (Nick Coghlan)
2. Re: A sorted version of **kwargs (M.-A. Lemburg)
3. Re: A sorted version of **kwargs (Guido van Rossum)
4. Re: A sorted version of **kwargs (Imri Goldberg)
5. Re: A sorted version of **kwargs (geremy condra)
----------------------------------------------------------------------
Message: 1
Date: Thu, 20 Jan 2011 23:11:57 +1000
From: Nick Coghlan <ncoghlan(a)gmail.com>
To: "Steven D'Aprano" <steve(a)pearwood.info>
Cc: python-ideas(a)python.org
Subject: Re: [Python-ideas] A sorted version of **kwargs
Message-ID:
<AANLkTik5XECCCBcgVvapyE4yEyCVAkN1-sFfaot+wbqE(a)mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On Thu, Jan 20, 2011 at 8:28 PM, Steven D'Aprano <steve(a)pearwood.info>
wrote:
> I would be +0 on making **kwargs an ordered dict automatically, and -1 on
> adding ***ordered_kwargs. Because kwargs is mostly used only for argument
> passing, and generally with only a small number of items, it probably
> doesn't matter too much if it's slightly slower than an unordered dict.
Yeah, simply making the kwargs dict always ordered is likely the way
we would do it. That's also the only solution with any chance of
working by default with the way most decorators are structured
(accepting *args and **kwargs and passing them to the wrapped
function).
To expand on Raymond's response in the previous thread on this topic,
there are likely a number of steps to this process:
1. Provide a _collections.OrderedDict C implementation
2. Create a PEP to gain agreement from other implementations
(especially IronPython, PyPy and Jython) to proceed with the remaining
steps
3. Make it a builtin class (odict?) in its own right (with
collections.OrderedDict becoming an alias for the builtin type)
4. Update the interpreter to use the new builtin type for kwargs containers
Use various microbenchmarks to check that the use of the new odict
builtin type instead of a plain dict doesn't slow things down too
much.
Cheers,
Nick.
--
Nick Coghlan?? |?? ncoghlan(a)gmail.com?? |?? Brisbane, Australia
------------------------------
Message: 2
Date: Thu, 20 Jan 2011 15:05:23 +0100
From: "M.-A. Lemburg" <mal(a)egenix.com>
To: Nick Coghlan <ncoghlan(a)gmail.com>
Cc: python-ideas(a)python.org
Subject: Re: [Python-ideas] A sorted version of **kwargs
Message-ID: <4D384123.6040105(a)egenix.com>
Content-Type: text/plain; charset=ISO-8859-1
Nick Coghlan wrote:
> On Thu, Jan 20, 2011 at 8:28 PM, Steven D'Aprano <steve(a)pearwood.info>
wrote:
>> I would be +0 on making **kwargs an ordered dict automatically, and -1 on
>> adding ***ordered_kwargs. Because kwargs is mostly used only for argument
>> passing, and generally with only a small number of items, it probably
>> doesn't matter too much if it's slightly slower than an unordered dict.
>
> Yeah, simply making the kwargs dict always ordered is likely the way
> we would do it. That's also the only solution with any chance of
> working by default with the way most decorators are structured
> (accepting *args and **kwargs and passing them to the wrapped
> function).
-1.
How often do you really need this ?
In which of those cases wouldn't a static code analysis give you
the call order of the parameters already ?
"Nice to have" is not good enough to warrant a slow down of
all function calls involving keyword arguments, adding overhead
for other Python implementations and possibly causing problems
with 3rd party extensions relying on getting a PyDict for the
keyword arguments object.
--
Marc-Andre Lemburg
eGenix.com
Professional Python Services directly from the Source (#1, Jan 20 2011)
>>> Python/Zope Consulting and Support ... http://www.egenix.com/
>>> mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/
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________________________________________________________________________
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http://www.egenix.com/company/contact/
------------------------------
Message: 3
Date: Thu, 20 Jan 2011 08:42:20 -0800
From: Guido van Rossum <guido(a)python.org>
To: "M.-A. Lemburg" <mal(a)egenix.com>
Cc: python-ideas(a)python.org
Subject: Re: [Python-ideas] A sorted version of **kwargs
Message-ID:
<AANLkTimQmVdoR-hMc3Gq9Md+_w7bvra6uV1K2NjZaWoZ(a)mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On Thu, Jan 20, 2011 at 6:05 AM, M.-A. Lemburg <mal(a)egenix.com> wrote:
> Nick Coghlan wrote:
>> On Thu, Jan 20, 2011 at 8:28 PM, Steven D'Aprano <steve(a)pearwood.info>
wrote:
>>> I would be +0 on making **kwargs an ordered dict automatically, and -1
on
>>> adding ***ordered_kwargs. Because kwargs is mostly used only for
argument
>>> passing, and generally with only a small number of items, it probably
>>> doesn't matter too much if it's slightly slower than an unordered dict.
>>
>> Yeah, simply making the kwargs dict always ordered is likely the way
>> we would do it. That's also the only solution with any chance of
>> working by default with the way most decorators are structured
>> (accepting *args and **kwargs and passing them to the wrapped
>> function).
>
> -1.
>
> How often do you really need this ?
>
> In which of those cases wouldn't a static code analysis give you
> the call order of the parameters already ??
>
> "Nice to have" is not good enough to warrant a slow down of
> all function calls involving keyword arguments, adding overhead
> for other Python implementations and possibly causing problems
> with 3rd party extensions relying on getting a PyDict for the
> keyword arguments object.
What he says.
In addition, I wonder what the semantics would be if the caller passed
**d where d was an *unordered* dict...
--
--Guido van Rossum (python.org/~guido)
------------------------------
Message: 4
Date: Thu, 20 Jan 2011 18:53:54 +0200
From: Imri Goldberg <lorgandon(a)gmail.com>
To: Guido van Rossum <guido(a)python.org>
Cc: python-ideas(a)python.org, "M.-A. Lemburg" <mal(a)egenix.com>
Subject: Re: [Python-ideas] A sorted version of **kwargs
Message-ID:
<AANLkTin0GApx57hHQXpQLZ00wmqC_zY_xxzyW8vpRgtN(a)mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
On Thu, Jan 20, 2011 at 6:42 PM, Guido van Rossum <guido(a)python.org> wrote:
>
> > -1.
> >
> > How often do you really need this ?
> >
> > In which of those cases wouldn't a static code analysis give you
> > the call order of the parameters already ?
> >
> > "Nice to have" is not good enough to warrant a slow down of
> > all function calls involving keyword arguments, adding overhead
> > for other Python implementations and possibly causing problems
> > with 3rd party extensions relying on getting a PyDict for the
> > keyword arguments object.
>
> What he says.
>
> In addition, I wonder what the semantics would be if the caller passed
> **d where d was an *unordered* dict...
What if the default behavior stays as it is today, but a magic decorator is
added, (maybe @ordered_kwargs or some such),
and only for these kind of functions the new behavior applies.
Also, given such a decorator, when given **d where d is a regular dict, the
implementation could possibly throw an error. (Or maybe it is up to the
implementor of the specific function).
Cheers,
Imri
--
Imri Goldberg
--------------------------------------
http://plnnr.com/ - automatic trip planning
http://www.algorithm.co.il/blogs/
--------------------------------------
-- insert signature here ----
Hi all,
There's a striking asymmetry between the wonderful flexibility in
passing values into functions (positional args, keyword args, default
values, *args, **kwargs, ...) and the limited options for processing
the return values (assignment).
Hence, whenever I upgrade a function with a new keyword arg and a
default value, I do not have to change any of the existing calls,
whereas whenever I add a new element to its output tuple, I find
myself chasing all existing code to upgrade the corresponding
assignments with an additional (unused) variable.
So I was wondering whether this was ever discussed before (and
recorded) inside the Python community.
(naively what seems to be missing is the ability to use the assignment
machinery that binds functions' formal params to the given actual
param list also in the context of a return value assignment)
cheers,
Luc
Hi,
By the way, a sorted **kwargs may slow down the speed of function invocation.
But we do not know how often the function gets called.
So we mustn't enforce the dict to be sorted for it unpredictable defects in
performance. I need to emphasize the UNPREDICTABLE.
Hongbao Chen
Software Engineering School
Xi'an Jiaotong University
Cell:+8613891979195
________________________________
发件人： "python-ideas-request(a)python.org" <python-ideas-request(a)python.org>
收件人： python-ideas(a)python.org
发送日期： 2011/1/21 (周五) 9:59:06 上午
主 题： Python-ideas Digest, Vol 50, Issue 36
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Today's Topics:
1. Re: A sorted version of **kwargs (Don Spaulding)
2. Re: A sorted version of **kwargs (MRAB)
3. Re: A sorted version of **kwargs (Alexander Belopolsky)
4. Re: A sorted version of **kwargs (Nick Coghlan)
5. Re: A sorted version of **kwargs (Hongbao Chen)
----------------------------------------------------------------------
Message: 1
Date: Thu, 20 Jan 2011 14:26:23 -0600
From: Don Spaulding <donspauldingii(a)gmail.com>
To: Bruce Leban <bruce(a)leapyear.org>
Cc: python-ideas(a)python.org
Subject: Re: [Python-ideas] A sorted version of **kwargs
Message-ID:
<AANLkTinvh22idu-PTNOEF=qu9njK4uBmxpc5LJ7CXW_6(a)mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
On Thu, Jan 20, 2011 at 2:05 PM, Bruce Leban <bruce(a)leapyear.org> wrote:
>
> On Thu, Jan 20, 2011 at 11:47 AM, Tim Delaney <timothy.c.delaney(a)gmail.com
> > wrote:
>
>>
>> ['b':1] would then be ambiguous (appears to be a slice of a list). More
>> obvious in the case of [1:2] ...
>>
>
> We use parenthesis for tuples and avoid the ambiguity by writing (1,).
> In the same way, we could require your examples to be written ['b':1,] and
> [1:2,]
>
Please, not this. I like the idea of syntactic support for the odict, but
no need to spread the (foo,) syntax around. It's too easy to misinterpret
when you do a quick scan of a body of code.
Hi there python-ideas!
Does it bother anyone else that it's so cumbersome to instantiate an
OrderedDict with ordered data?
>>> from collections import OrderedDict
>>> OrderedDict(b=1,a=2)
OrderedDict([('a', 2), ('b', 1)]) # Order lost. Boooo.
>>> OrderedDict([('b',1),('a',2)])
OrderedDict([('b', 1), ('a', 2)])
Obviously, OrderedDict's __init__ method (like all other functions) never
gets a chance to see the kwargs dict in the order it was specified. It's
usually faked by accepting the sequence of (key, val) tuples, as above. I
personally think it would be nice to be able to ask the interpreter to keep
track of the order of the arguments to my function, something like:
def sweet_function_name(*args, **kwargs, ***an_odict_of_kwargs):
pass
I'm not married to the syntax. What do you think about the idea?
