New submission from Andreas H. <ahanga...@gmx.net>:
The __eq__ method of ForwardRef does not take into account the module
parameter.
However, ForwardRefs with dissimilar module parameters are referring to
different types even if they have different name. Thus also the ForwardRef's
with same name but different module, should not be considered equal.
Consider the following code
from typing import *
ZZ = Optional['YY']
YY = int
YY = Tuple[Optional[ForwardRef("YY", module=__name__)], int]
print( YY.__args__[0].__args__[0].__forward_module__ )
# this prints None, but should print __main__ (or whatever __name__ contains)
When the first ForwardRef is not created, the program behaves correctly
#ZZ = Optional['YY']
YY = int
YY = Tuple[Optional[ForwardRef("YY", module=__name__)], int]
print( YY.__args__[0].__args__[0].__forward_module__ )
# this prints __main__ (or whatever __name__ contains)
The issue is that the line `ZZ = Optional['YY']` creates a cache entry, which
is re-used instead of the second definition `Optional[ForwardRef("YY",
module=__name__)]` and thus shadows the different argument of ForwardRef.
This problem could be fixed if the __eq__ method of FowardRef also checks for
module equality.
i.e. in ForwardRef.__eq__ in typing.py replace
return self.__forward_arg__ == other.__forward_arg__
with
return self.__forward_arg__ == other.__forward_arg__ and
self.__forward__module__ == other.__forward__module__
Ideally, (and for consistency reasons) the `__repr__` method of `ForwardRef`
would also include the module arg if it present:
Change:
def __repr__(self):
return f'ForwardRef({self.__forward_arg__!r})'
to
def __repr__(self):
if self.__forward_module__ is None:
return f'ForwardRef({self.__forward_arg__!r})'
else:
return f'ForwardRef({self.__forward_arg__!r},
module={self.__forward__module!r})'
----------
components: Library (Lib)
messages: 410221
nosy: andreash, gvanrossum, kj
priority: normal
severity: normal
status: open
title: ForwardRef.__eq__ does not respect module parameter
type: behavior
versions: Python 3.10, Python 3.9
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue46333>
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