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Unioned types should be hashable: not documented? #112281
Description
Documentation
It seems that typing.Union[X, Y] as well as X | Y type hints require X and Y to be hashable.
This is not documented as far as I can see.
Considering this example:
@dataclass
class ValueRange:
lo: int
hi: int
T1 = Annotated[int, ValueRange(-10, 5)]This fails when unioned:
>>> Annotated[int, ValueRange(-10, 5)] | None
(...)
File "/usr/lib64/python3.11/typing.py", line 1375, in __or__
return Union[self, right]
~~~~~^^^^^^^^^^^^^
File "/usr/lib64/python3.11/typing.py", line 358, in inner
return func(*args, **kwds)
^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/python3.11/typing.py", line 481, in __getitem__
return self._getitem(self, parameters)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/python3.11/typing.py", line 695, in Union
parameters = _remove_dups_flatten(parameters)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/python3.11/typing.py", line 326, in _remove_dups_flatten
return tuple(_deduplicate(params))
^^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/python3.11/typing.py", line 301, in _deduplicate
all_params = set(params)
^^^^^^^^^^^
File "/usr/lib64/python3.11/typing.py", line 2151, in __hash__
return hash((self.__origin__, self.__metadata__))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: unhashable type: 'ValueRange'Should this be documented say here: https://docs.python.org/3/library/typing.html?highlight=typing#typing.Annotated ?
And examples here should use frozen dataclasses: https://docs.python.org/3/library/typing.html?highlight=typing#typing.Annotated ?
Activity
sobolevn commentedon Nov 20, 2023
PEPs https://peps.python.org/pep-0593/#specification and https://peps.python.org/pep-0604/ do not say anything about requirement of items to be hashable. I think that this is a bug: unhashable items must be allowed.
I think that we need to rework our
_deduplicatefunction. I have an idea on how to do it :)Thanks for the report! 👍
sobolevn commentedon Nov 20, 2023
This is more complex than I initially thought, because
_UnionGenericAliasalso usessetto compare results. So, we need a slow way of doing it as well. Seecpython/Lib/typing.py
Line 1536 in ce1096f
pythongh-112281: Allow `Union` with unhashable `Annotated` metadata
gh-112281: Allow `Union` with unhashable `Annotated` metadata (#112283)
pythongh-112281: Allow `Union` with unhashable `Annotated` metadata (p…
[3.12] gh-112281: Allow `Union` with unhashable `Annotated` metadata (G…
[3.11] pythongh-112281: Allow `Union` with unhashable `Annotated` met…
[3.11] gh-112281: Allow `Union` with unhashable `Annotated` metadata (G…
pythongh-112281: Allow `Union` with unhashable `Annotated` metadata (p…
pythongh-112281: Allow `Union` with unhashable `Annotated` metadata (p…
pythongh-112281: Allow `Union` with unhashable `Annotated` metadata (p…