Narrow types after 'in' operator #4072
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As discussed in #4099 (comment), let's only do this for optional types, since other cases can be unsafe because of operator overloading, and these other cases seem pretty rare anyway. |
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OK, I will do this later this evening or tomorrow morning. |
Done! |
mypy/checker.py
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| @@ -2874,6 +2874,27 @@ def remove_optional(typ: Type) -> Type: | |||
| return typ | |||
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| def builtin_item_type(tp: Type) -> Optional[Type]: | |||
| # This is only OK for built-in containers, where we know the behavior of __contains__. | |||
test-data/unit/check-isinstance.test
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| [case testNarrowTypeAfterInDict] | ||
| # flags: --strict-optional | ||
| from typing import Dict, Optional | ||
| x: Dict[str, str] |
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Use a different type for values to make sure that this works against the key type.
| # flags: --strict-optional | ||
| from typing import List, Optional | ||
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| x: List[int] |
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Add test for optional item type (e.g. List[Optional[int]]).
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@JukkaL Thanks for review! I implemented the changes in the new commit. |
| # flags: --strict-optional | ||
| from typing import List, Optional | ||
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| x: List[Optional[int]] |
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Here's another special case: What if the container is a nested one, say List[List[x]], where x might be Any? How do we deal with various item types, such as List[int] and List[Any]?
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a) If the container is List[Any], then we do nothing (there is a test for this).
b) If the container is List[List[Any]] we narrow the type (provided there is an overlap, this is consistent with how == currently treated), for example:
x: Optional[int]
lst: Optional[List[int]]
nested: List[List[Any]]
if lst in nested:
reveal_type(lst) # List[int]
if x in nested:
reveal_type(x) # Optional[int]There is already a test for non-overlapping items int vs str. I will add one more test for other (nested) types?
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OK, added one more test.
Fixes #4071
This is separated from #4070 plus added various tests.