[conflict] Allow assignment of types with Nones without explicit annotation
#2225
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Currently, mypy will not infer types containing None unless they are valid PartialTypes (i.e. are bare None, list, set, or dict). This means that all assignments of such types must be explicitly annotated. It doesn't make sense to require this with strict Optional, as None is a perfectly valid type. This PR makes types containing None valid inference targets. Fixes #2195.
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JukkaL
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Oct 11, 2016
| [case testOptionalNonPartialTypeWithNone] | ||
| from typing import Generator | ||
| def f() -> Generator[str, None, None]: pass | ||
| x = f() |
JukkaL
reviewed
Oct 11, 2016
| from typing import Generator | ||
| def f() -> Generator[str, None, None]: pass | ||
| x = f() | ||
| l = [f()] |
JukkaL
reviewed
Oct 11, 2016
| if not is_valid_inferred_type(arg): | ||
| return False | ||
| fullname = typ.type.fullname() | ||
| if ((fullname == 'builtins.list' or |
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I assume that these are special cased as a convenience, as collections with all None types are rarely useful and thus we require them to be annotated, but for other generic types all None args may be totally reasonable. This seems pretty reasonable to me, but it's worth adding a comment here about why we special case just these types.
Also, can you add tests for the special casing?
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Other than the notes above (and the merge conflict), LGTM! |
gvanrossum
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Nones without explicit annotationNones without explicit annotation
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I'm going to drop this PR, as fixing #2246 should fix this too (and more cleanly, at that). |
gvanrossum
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Oct 22, 2016
This means mypy will no longer give Need type annotation for variable errors for assignments with values of type Generator[str, None, None] or List[None] or similar. However, lists, sets, and dicts that are initialized with None values that were previously inferred may now need type annotations. I.e. constructs that look like: x = [None] x.append(0) will now be type errors unless they have explicit annotations. Supplants #2225. Fixes #2246. Fixes #2195. Fixes #2258.
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Currently, mypy will not infer types containing None unless they are
valid PartialTypes (i.e. are bare None, list, set, or dict). This means
that all assignments of such types must be explicitly annotated.
It doesn't make sense to require this with strict Optional, as None is a
perfectly valid type. This PR makes types containing None valid
inference targets.
Fixes #2195.