New submission from Adam Paszke <adam.pas...@gmail.com>:
Hi everyone,
I have a module that needs to inspect type annotations on a few functions. One
of the types I need to special case on is typing.Tuple, and I used code like
this to detect it:
if getattr(annotation, '__origin__', None) == typing.Tuple:
...
else:
...
This was based on the comment from the typing module (Lib/typing.py:609) that
specified this particular invariant on the __origin__ attribute:
> __origin__ keeps a reference to a type that was subscripted,
e.g., Union[T, int].__origin__ == Union;
Everything worked just fine until I checked it on the alpha release of Python
3.7 in my CI. Turns out, that in that release we have
typing.Tuple[str, int].__origin__ == tuple
and not (which is the case in e.g. 3.6)
typing.Tuple[str, int].__origin__ == typing.Tuple
I know this is not a documented attribute, so it can change, but I wanted to
highlight that it's either a regression, or the comment will need to be
updated, so people won't try to depend on that.
----------
components: Library (Lib)
messages: 316127
nosy: apaszke
priority: normal
severity: normal
status: open
title: __origin__ invariant broken
type: behavior
versions: Python 3.7, Python 3.8
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue33420>
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