feat: proper narrowing for TypedDict keys and values #19610
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| reveal_type(p) # N: Revealed type is "TypedDict('__main__.Point', {'x': builtins.int, 'y': builtins.int})" | ||
| # Use values() to check fallback value type. | ||
| reveal_type(p.values()) # N: Revealed type is "typing.Iterable[builtins.object]" | ||
| reveal_type(p.values()) # N: Revealed type is "typing.ValuesView[builtins.int]" |
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This is incorrect since the TypedDict is not closed, so there may be other values that are not of this type.
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Wait why isn't it closed? If you try to set p['not-present'] = 123 you will get an error from mypy
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There can be subclasses. The upcoming PEP 728 addresses this.
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Diff from mypy_primer, showing the effect of this PR on open source code: scrapy (https://github.com/scrapy/scrapy)
+ scrapy/utils/request.py:230: error: If x = b'abc' then f"{x}" or "{}".format(x) produces "b'abc'", not "abc". If this is desired behavior, use f"{x!r}" or "{!r}".format(x). Otherwise, decode the bytes [str-bytes-safe]
yarl (https://github.com/aio-libs/yarl)
+ tests/test_cache.py:18:12: error: Non-overlapping equality check (left operand type: "KeysView[Literal['idna_encode', 'idna_decode', 'ip_address', 'host_validate', 'encode_host']]", right operand type: "set[str]") [comparison-overlap]
+ tests/test_cache.py:18:12: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-comparison-overlap for more info
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This PR enhances type narrowing for
TypedDict.keysandTypedDict.values.Keys will now type as a Union of Literals and values will type as a Union of the value types.
I will do
TypedDict.itemsin a separate PR, as I'm having trouble with the typeshed.(Explain how this PR changes mypy.)