[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Petr Viktorin]

Change by Petr Viktorin :


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stage: patch review -> resolved
status: open -> closed

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Petr Viktorin]

Petr Viktorin  added the comment:


New changeset fcef60f59d04c63b3540b4c4886226098c1bacd1 by Petr Viktorin (Jeroen 
Demeyer) in branch 'master':
bpo-33261: guard access to __code__ attribute in inspect (GH-6448)
https://github.com/python/cpython/commit/fcef60f59d04c63b3540b4c4886226098c1bacd1


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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Petr Viktorin]

Petr Viktorin  added the comment:

I just reviewed, and I plan to merge it if I don't see any pushback from the 
others.
Sorry for the extreme delay.

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nosy: +petr.viktorin

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Jeroen Demeyer]

Jeroen Demeyer  added the comment:

Can somebody please review PR 6448?

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Jeroen Demeyer]

Jeroen Demeyer  added the comment:

Can we please go back to the original issue? If you think that __code__ should 
be an alias for __call__.__code__, that is a different issue.

On https://github.com/python/cpython/pull/6448#issuecomment-381507329 I posted 
an alternative solution for the problem. Is either the original PR or the new 
variant acceptable?

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Nick Coghlan]

Nick Coghlan  added the comment:

Terry, if you'd like to continue that discussion, please open a new enhancement 
request for 3.8+ against the inspect module asking for the affected 
introspection functions to recursively search for relevant attributes, the same 
way `inspect.signature` digs inside different object types to look for 
signature information.

However, the fact the inspect module doesn't implement that search for relevant 
attributes today is *not* a bug - it's a past design decision that could 
potentially stand to be revisited.

By contrast, the fact the affected functions throw AttributeError instead of 
returning False for a missing attribute *is* a bug.

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Jeroen Demeyer]

Jeroen Demeyer  added the comment:

> I would like python_coded_callable.__code__ to be the code object executed 
> when python_coded_callable is called

First of all, that doesn't answer the question of what to do with non-Python 
coded callables where there is no __code__ object at all.

Second, are you *really* sure that you want that? That would mean adding a 
__code__ attribute to all callable Python classes or adding a __code__ 
descriptor to "type".

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Terry J. Reedy]

Terry J. Reedy  added the comment:

I would like python_coded_callable.__code__ to be the code object executed when 
python_coded_callable is called, just as expected by the isxyz author(s).  It 
has to exist somewhere.  Methods m and m3 both return 42 when called, and both 
have the same code object.

>>> m3.__code__

>>> m3.__func__.__code__

>>> m.__func__.__call__.__code__


The fact that m requires an additional level of indirection is an 
implementation detail that I don't think necessarily has to involve users.

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Jeroen Demeyer]

Jeroen Demeyer  added the comment:

The only attributes that a method is guaranteed to have are __func__ and 
__self__ (which are the arguments passed to the MethodType constructor).

All other attributes are looked up through __func__ by the C version of the 
following Python code:

def __getattr__(self, attr):
return getattr(self.__func__, attr)

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Jeroen Demeyer]

Jeroen Demeyer  added the comment:

> I am wondering if, instead, the bug is in m, the object returned by 
> MethodType, or in attribute lookup thereupon.

What would you expect m.__code__ to return then? Methods support arbitrary 
callables and certainly not all callables have a meaningful __code__.

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Nick Coghlan]

Nick Coghlan  added the comment:

The inspect functions throwing an exception when handed a method wrapping a 
non-function callable instead of returning False is a definite bug.

The behaviour of MethodType when handed a non-function callable is cryptic, but 
not actually a bug: the problem is that it expects to be able to delegate 
accesses to __name__ and __code__ to the underlying callable.

A docs bug to clarify exactly which accesses are going to get delegated would 
make sense (and perhaps make MethodType.__dir__ a bit smarter about that 
delegation), but it's a separate issue from the one Jeroen has reported here.

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Terry J. Reedy]

Terry J. Reedy  added the comment:

Nick and Raymond, I added both of you as nosy because, among other reasons, you 
commented on the latest version of PEP575.

I agree that there is a bug in current CPython, in that the is* functions 
should return, not raise, but I am not sure where is it, and hence if the PR is 
the right fix.  I am wondering if, instead, the bug is in m, the object 
returned by MethodType, or in attribute lookup thereupon.

MethodType is the type of bound user-defined (Python-coded) functions and 
ismethod is true for instances thereof.  Consider 4 other bound methods, two 
'normal'(callable is method of instance class) and two, like Jeroen's, 'odd' 
(callable not related to int).

>>> cm = Callable().__call__
>>> cm.__code__
", line 2>
>>> cm.__name__
'__call__'

>>> cm2 = MethodType(Callable.__call__, Callable())
>>> cm2.__code__
", line 2>
>>> cm2.__name__
'__call__'

>>> m2 = MethodType(Callable.__call__, 42)
>>> m2.__code__
", line 2>
>>> m2.__name__
'__call__'
>>> m2()
()

>>> m3 = MethodType(Callable().__call__, 42)
>>> m3.__code__
", line 2>
>>> m3.__name__
'__call__'
>>> m3()
(42,)

>>> m = MethodType(Callable(), 42)
>>> m.__code__
... AttributeError: 'Callable' object has no attribute '__code__'
>>> m.__name__
... AttributeError: 'Callable' object has no attribute '__name__'
>>> m()
(42,)

They all have the same attributes exposed by dir(), which omits both'__name__', 
promised in the docstring for ismethod*, and '__code__', assumed by the is--- 
functions under discussion.

>>> dir(cm) == dir(cm2) == dir(m) == dir(m2) == dir(m3)
True
>>> ('__code__' in dir(cm)) or ('__name__' in dir(cm))
False

However, accessing those names anyway, as (hidden) attributes, works for all 
but m.  Should doing so also work for m?  (If not, the ismethod docstring 
should not 'guarantee' .__name__.)

* "Instance method objects provide these attributes:
__doc__ documentation string
__name__name with which this method was defined
..."

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nosy: +ncoghlan, rhettinger, terry.reedy

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Jeroen Demeyer]

Change by Jeroen Demeyer :


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keywords: +patch
pull_requests: +6144
stage:  -> patch review

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[issue33261] inspect.isgeneratorfunction fails on hand-created methods

[Jeroen Demeyer]

New submission from Jeroen Demeyer :

The inspect functions isgeneratorfunction, iscoroutinefunction, 
isasyncgenfunction can fail on methods that do not have a __code__ attribute:

>>> from types import MethodType
>>> class Callable:
... def __call__(self, *args):
... return args
>>> m = MethodType(Callable(), 42)
>>> m()
(42,)
>>> import inspect
>>> inspect.iscoroutinefunction(m)
Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/lib64/python3.6/inspect.py", line 186, in iscoroutinefunction
object.__code__.co_flags & CO_COROUTINE)
AttributeError: 'Callable' object has no attribute '__code__'

This was discovered while working on PEP 575, but it is really an independent 
issue that should be fixed anyway.

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components: Library (Lib)
messages: 315187
nosy: jdemeyer
priority: normal
severity: normal
status: open
title: inspect.isgeneratorfunction fails on hand-created methods
type: behavior
versions: Python 3.6, Python 3.7, Python 3.8

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