Should operator `|` on `TypedDict` allow for creating intersection-like dicts?
還沒有人認領這個 Issue。
評估
研究方向
先比較 PEP 584 和 PEP 589，然後在連結的 mypy playground 中重現 TypedDict 範例。檢視相關的 typing、Pylance 和 Pyright 討論，以判斷對於所提議的類似交集行為是否有共識。達成一致的語意，並記錄 type checker 支援該行為的途徑後，即可視為完成。
由索引模型根據 Issue 內容生成。
描述
I'm wondering how is the relation between the following PEPs:
- PEP 584 which introduces operator
|for dicts, but doesn't mention how it should behave forTypedDict. - PEP 589 which introduces
TypedDict, but doesn't mention the operator|.
According to PEP 589, multiple inheritance can be used to create a combined (or "intersection like") dict, and operator | provides the corresponding behavior at runtime. Thus it would be nice if the type system could handle the combination properly (similar to how it is possible in TypeScript):
from typing import TypedDict
class HasFoo(TypedDict):
foo: int
class HasBar(TypedDict):
bar: int
class HasFooAndBar(HasFoo, HasBar):
...
def f(a: HasFoo, b: HasBar) -> HasFooAndBar:
return a | b
From a runtime and type-checking perspective this code looks valid, but currently mypy does not accept it (playground):
main.py:15: error: Incompatible return value type (got "HasFoo", expected "HasFooAndBar") [return-value]
main.py:15: error: Unsupported operand types for | ("HasFoo" and "HasBar") [operator]
Pyright seems to have the same behavior.
Apparently operator | can only be used for two instances of the same typed dict, which as far as I can see has limited use cases, because using the operator | on two dicts that already have the same fields is kind of pointless (perhaps it mostly makes sense if the type used total=False).
Possible related discussions and issues I've found:
- https://github.com/python/typing/issues/213 (since this feature for
TypedDictprobably falls into the "intersection type" category as well?) - https://github.com/microsoft/pylance-release/issues/2300
- https://github.com/microsoft/pyright/issues/2951
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