我想定义一个通用类型。就像是:
T = TypeVar('T')
RecurSeqOf = Sequence[Union[Generic[T], Sequence[T]]]
# mypy error: Variable "typing.Generic" is not valid as a type
有办法吗?
整个背景
实际上,我需要像这样的递归泛型类型
T = TypeVar('T')
RecurSeqOf = Sequence[Union[T, 'RecurSeqOf']]]
但是mypy尚不支持递归类型的定义:https : //github.com/python/mypy/issues/731
这就是为什么我通过使嵌套类型定义达到有限的深度来解决此问题的原因(例如,通常为5-6个级别,但是在此示例中,为简明起见,下面的两个级别)。因此,更需要缩短模式,因为我需要将其用于不同的参数类型:
from typing import Sequence, Union, TypeVar, Generic
class A:
pass
class B:
pass
# RecurSeqOfA = Sequence[Union[A, 'RecurSeqOfA']] # mypy error: Cannot resolve name "RecurSeqOfA" (possible cyclic definition)
RecurSeqOfA = Sequence[Union[A, Sequence[Union[A, Sequence[A]]]]]
# RecurSeqOfA = Sequence[Union[A, 'RecurSeqOfA']] # mypy error: Cannot resolve name "RecurSeqOfA" (possible cyclic definition)
RecurSeqOfB = Sequence[Union[B, Sequence[Union[B, Sequence[B]]]]]
T = TypeVar('T')
# RecurSeqOf = Sequence[Union[Generic[T], 'RecurSeqOf']] # error: Cannot resolve name "RecurSeqOf" (possible cyclic definition)
# additionally: error: Variable "typing.Generic" is not valid as a type
RecurSeqOf = Sequence[Union[Generic[T], Sequence[Generic[T]]]] # error: Variable "typing.Generic" is not valid as a type
正如宫城先生的评论所建议的:
from typing import TypeVar, MutableSequence
T = TypeVar('T', bound='RecurSeqOf')
RecurSeqOf = MutableSequence[T]
a: RecurSeqOf[str] = []
a.append("abc")
a.append([]) # mypy error: error: Argument 1 to "append" of "MutableSequence" has incompatible type "List[<nothing>]"; expected "str"
b: RecurSeqOf[str] = []
a.append(b) # mypy error: Argument 1 to "append" of "MutableSequence" has incompatible type "MutableSequence[str]"; expected "str"
a.append(["cde"]) # mypy error: Argument 1 to "append" of "MutableSequence" has incompatible type "List[str]"; expected "str"
该定义本身被mypy接受。但这并没有达到预期的效果。
由于Sequence
已经是通用的,因此可以直接使用类型变量:
from typing import TypeVar, Sequence, Union
T = TypeVar('T')
# [T, ...] | [[T, ...], ...]
RecurSeqOf = Sequence[Union[T, Sequence[T]]]
# T | [T, ...] | [[T, ...], ...]
RecurSeqOfUnion = Union[RecurSeqOf[T], T]
这就是文档所说的“用户定义的通用类型别名”。RecurSeqOf = ...
定义别名,并且Sequence[Union[T, Sequence[T]]]
是通用的。
这允许定义固定但任意深度的递归类型:
a0: RecurSeqOf[int]
a1: RecurSeqOf[RecurSeqOfUnion[int]]
a2: RecurSeqOf[RecurSeqOfUnion[RecurSeqOfUnion[int]]]
reveal_type(a0) # typing.Sequence[Union[builtins.int, typing.Sequence[builtins.int]]]
reveal_type(a1) # typing.Sequence[Union[typing.Sequence[Union[builtins.int, typing.Sequence[builtins.int]]], builtins.int, typing.Sequence[Union[typing.Sequence[Union[builtins.int, typing.Sequence[builtins.int]]], builtins.int]]]]
reveal_type(a2) # typing.Sequence[Union[typing.Sequence[Union[typing.Sequence[Union[builtins.int, typing.Sequence[builtins.int]]], builtins.int, typing.Sequence[Union[typing.Sequence[Union[builtins.int, typing.Sequence[builtins.int]]], builtins.int]]]], typing.Sequence[Union[builtins.int, typing.Sequence[builtins.int]]], builtins.int, typing.Sequence[Union[typing.Sequence[Union[typing.Sequence[Union[builtins.int, typing.Sequence[builtins.int]]], builtins.int, typing.Sequence[Union[typing.Sequence[Union[builtins.int, typing.Sequence[builtins.int]]], builtins.int]]]], typing.Sequence[Union[builtins.int, typing.Sequence[builtins.int]]], builtins.int]]]]
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