[New-bugs-announce] [issue42786] Different repr for collections.abc.Callable and typing.Callable

[Svyatoslav]

New submission from Svyatoslav <prometheus3375 at gmail.com>:

Was making some typing conversions to string and noticed a different behavior of collections.abc.Callable and typing.Callable here in 3.9.1. Issues issue42195 and issue40494 can be related.

>>> import collections, typing
>>> repr(collections.abc.Callable[[int], str])
"collections.abc.Callable[[<class 'int'>], str]"
>>> repr(typing.Callable[[int], str])
'typing.Callable[[int], str]'

The variant from collections is wrong, it is not consistent with other GenericAlias reprs like
>>> repr(tuple[list[float], int, str])
'tuple[list[float], int, str]'

The problem is actually in the list usage to denote callable arguments:
>>> repr(tuple[[float], int, str])
"tuple[[<class 'float'>], int, str]"

Here is the same error. This error disallows to use typing in eval/exec statements:
>>> c = collections.abc.Callable[[int], str]
>>> d = eval(repr(c))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1
    collections.abc.Callable[[<class 'int'>], str]
                              ^
SyntaxError: invalid syntax

Ofc there is no such problem with typing.Callable:
>>> c = typing.Callable[[int], str]
>>> d = eval(repr(c))
>>> 

Interesting, if pass a list into typing.Tuple, an exception is raised:
>>> repr(typing.Tuple[[float], int, str])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "f:\software\python3.9\lib\typing.py", line 262, in inner
    return func(*args, **kwds)
  File "f:\software\python3.9\lib\typing.py", line 896, in __getitem__
    params = tuple(_type_check(p, msg) for p in params)
  File "f:\software\python3.9\lib\typing.py", line 896, in <genexpr>
    params = tuple(_type_check(p, msg) for p in params)
  File "f:\software\python3.9\lib\typing.py", line 151, in _type_check
    raise TypeError(f"{msg} Got {arg!r:.100}.")
TypeError: Tuple[t0, t1, ...]: each t must be a type. Got [<class 'float'>].

I think it is not correct that tuple accepts lists as generics, i. e. for tuple[[float], int, str] an exception as above should be raised. Bu this is the topic for other issue (maybe even already reported).

----------
messages: 384068
nosy: Prometheus3375
priority: normal
severity: normal
status: open
title: Different repr for collections.abc.Callable and typing.Callable
type: behavior
versions: Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42786>
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