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Tests subtyping rules for protocols.
"""
# Specification: https://typing.readthedocs.io/en/latest/spec/protocol.html#subtyping-relationships-with-other-types
# > Protocols cannot be instantiated.
from typing import Hashable, Iterable, Protocol, Sequence, TypeVar
class Proto1(Protocol):
pass
p1 = Proto1() # E: protocol cannot be instantiated
# > A protocol is never a subtype of a concrete type.
# > A concrete type X is a subtype of protocol P if and only if X implements
# > all protocol members of P with compatible types. In other words, subtyping
# > with respect to a protocol is always structural.
class Proto2(Protocol):
def method1(self) -> None:
...
class Concrete2:
def method1(self) -> None:
pass
def func1(p2: Proto2, c2: Concrete2):
v1: Proto2 = c2 # OK
v2: Concrete2 = p2 # E
# > A protocol P1 is a subtype of another protocol P2 if P1 defines all
# > protocol members of P2 with compatible types.
class Proto3(Protocol):
def method1(self) -> None:
...
def method2(self) -> None:
...
def func2(p2: Proto2, p3: Proto3):
v1: Proto2 = p3 # OK
v2: Proto3 = p2 # E
# > Generic protocols follow the rules for generic abstract classes, except
# > for using structural compatibility instead of compatibility defined by
# > inheritance relationships.
S = TypeVar("S")
T = TypeVar("T")
class Proto4(Protocol[S, T]):
def method1(self, a: S, b: T) -> tuple[S, T]:
...
class Proto5(Protocol[T]):
def method1(self, a: T, b: T) -> tuple[T, T]:
...
def func3(p4_int: Proto4[int, int], p5_int: Proto5[int]):
v1: Proto4[int, int] = p5_int # OK
v2: Proto5[int] = p4_int # OK
v3: Proto4[int, float] = p5_int # E
v4: Proto5[float] = p4_int # E
S_co = TypeVar("S_co", covariant=True)
T_contra = TypeVar("T_contra", contravariant=True)
class Proto6(Protocol[S_co, T_contra]):
def method1(self, a: T_contra) -> Sequence[S_co]:
...
class Proto7(Protocol[S_co, T_contra]):
def method1(self, a: T_contra) -> Sequence[S_co]:
...
def func4(p6: Proto6[float, float]):
v1: Proto7[object, int] = p6 # OK
v2: Proto7[float, float] = p6 # OK
v3: Proto7[complex, int] = p6 # OK
v4: Proto7[int, float] = p6 # E
v5: Proto7[float, object] = p6 # E
# > Unions of protocol classes behaves the same way as for non-protocol classes.
class SupportsExit(Protocol):
def exit(self) -> int:
...
class SupportsQuit(Protocol):
def quit(self) -> int | None:
...
def finish(task: SupportsExit | SupportsQuit) -> int:
return 0
class DefaultJob:
def quit(self) -> int:
return 0
finish(DefaultJob()) # OK
# > One can use multiple inheritance to define an intersection of protocols.
class HashableFloats(Iterable[float], Hashable, Protocol):
pass
def cached_func(args: HashableFloats) -> float:
return 0.0
cached_func((1, 2, 3)) # OK, tuple is both hashable and iterable
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