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hauntsaninja merged 1 commit into from
Oct 27, 2022
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Add type inference for dict.keys membership #13372

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Add type inference for dict.keys membership 
Also for containership checks on `typing.KeysView.` This is to bring the
following cases into alignment:

    from typing import KeysView

    key: str | None
    d: dict[str, int]
    kv: KeysView[str]

    if key in d:
        # type of 'key' is inferred to be 'str'
        ...

    if key in d.keys():
        # type of 'key' should be inferred to be 'str'
        ...

    if key in kv:
        # type of 'key' should be inferred to be 'str'
        ...

Before this change only the first `if` would narrow the type of `key`.

I've just added a test under `test-data/unit/pythoneval.test` as
`test-data/unit/fixtures/dict.pyi` doesn't include `dict.keys`, and
adding it requires importing `dict_keys` from `_collections_abc` in
those stubs, which then requires adding `_collections_abc.pyi` stubs,
which would have to be complete since e.g.
`testGenericAliasCollectionsABCReveal` expects most of the types in
those stubs to be defined (this is the same approach as
7678f28).

GH: issue #13360
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@matthewhughes934 Matt Hughes
matthewhughes934 authored and Matt Hughes committed Aug 23, 2022
commit 75ca813a0428a8db2be7c356535e123fb5da4bac
2 changes: 2 additions & 0 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6329,6 +6329,8 @@ def builtin_item_type(tp: Type) -> Type | None:
"builtins.dict",
"builtins.set",
"builtins.frozenset",
"_collections_abc.dict_keys",

@sobolevn sobolevn Aug 9, 2022

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What about typing.KeysView? https://github.com/python/cpython/blob/70fc9641b56144854777aef29c145cd10789e3df/Lib/typing.py#L2701

And collections.abc.KeysView?
What about ValuesView and ItemsView?

@sobolevn sobolevn Aug 9, 2022

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And dict_values as well as dict_items 🙂

@matthewhughes934 matthewhughes934 Aug 9, 2022

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What about typing.KeysView?

Sounds good. I wasn't sure exactly what would be best to be included in this changeset. Let me drag all of those in too

@matthewhughes934 matthewhughes934 Aug 24, 2022

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What about typing.KeysView? https://github.com/python/cpython/blob/70fc9641b56144854777aef29c145cd10789e3df/Lib/typing.py#L2701

This is included with 75ca813

"typing.KeysView",
]:
if not tp.args:
# TODO: fix tuple in lib-stub/builtins.pyi (it should be generic).
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24 changes: 24 additions & 0 deletions test-data/unit/pythoneval.test
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Expand Up @@ -1636,3 +1636,27 @@ foo("")
foo(list(""))
foo(list((list(""), "")))
[out]

[case testNarrowTypeForDictKeys]
# flags: --strict-optional
from typing import Dict, KeysView, Optional

d: Dict[str, int]
key: Optional[str]
if key in d.keys():
reveal_type(key)
else:
reveal_type(key)

kv: KeysView[str]
k: Optional[str]
if k in kv:
reveal_type(k)
else:
reveal_type(k)

[out]
_testNarrowTypeForDictKeys.py:7: note: Revealed type is "builtins.str"
_testNarrowTypeForDictKeys.py:9: note: Revealed type is "Union[builtins.str, None]"
_testNarrowTypeForDictKeys.py:14: note: Revealed type is "builtins.str"
_testNarrowTypeForDictKeys.py:16: note: Revealed type is "Union[builtins.str, None]"