PEP 484: Clarify definition of AnyStr #744
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The definition of AnyStr as given makes sense only in Python 3, as observed by @srittau. To prevent confusion, this PR changes the definition to use Text instead of str. I also changed the two places where AnyStr was defined as an example, and made a few other related adjustments: - Remove mention of None as modifying the type, which is not true as of python#689. - Move Text up in the list of convenience definition because we now need it for the definition of AnyStr. - Modify definition of Optional to use `None` instead of `type(None)`, because the latter is not a valid static type.
gvanrossum
approved these changes
Jul 21, 2018
| @@ -1357,8 +1357,7 @@ without specifying the actual default value. For example:: | |||
| def foo(x: AnyStr, y: AnyStr = ...) -> AnyStr: ... | |||
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| What should the default value look like? Any of the options ``""``, | |||
| ``b""`` or ``None`` fails to satisfy the type constraint (actually, | |||
| ``None`` will *modify* the type to become ``Optional[AnyStr]``). | |||
| ``b""`` or ``None`` fails to satisfy the type constraint. | |||
| * Optional, defined by ``Optional[t] == Union[t, type(None)]`` | ||
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| * AnyStr, defined as ``TypeVar('AnyStr', str, bytes)`` | ||
| * Optional, defined by ``Optional[t] == Union[t, None]`` |
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Another good call. Perhaps the section on "Using None" should also be revised? It currently says
When used in a type hint, the expression
Noneis considered equivalent totype(None).
But that's false -- at least for mypy, and IIRC we once discussed this and decided that this is intentional: type(None) is not acceptable at all in type hints!
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The definition of AnyStr as given makes sense only in Python 3, as observed by @srittau. To prevent confusion, this PR changes the definition to use Text instead of str.
I also changed the two places where AnyStr was defined as an example, and made a few other related adjustments:
Noneinstead oftype(None), because the latter is not a valid static type.