""" Tests the basic definition rules for protocols. """ # Specification: https://typing.readthedocs.io/en/latest/spec/protocol.html#defining-a-protocol from abc import abstractmethod from typing import Any, ClassVar, Iterable, NamedTuple, Protocol, Sequence from dataclasses import dataclass class SupportsClose(Protocol): def close(self) -> None: ... class Resource: def close(self) -> None: pass def close_all(things: Iterable[SupportsClose]) -> None: for t in things: t.close() f = open("foo.txt") r = Resource() close_all([f, r]) # OK close_all([1]) # E: 'int' has no 'close' method class Example(Protocol): def first(self) -> int: # This is a protocol member return 42 @abstractmethod def second(self) -> int: # Method without a default implementation raise NotImplementedError # > Static methods, class methods, and properties are equally allowed in protocols. @staticmethod def third() -> int: ... @classmethod def fourth(cls) -> int: ... @property def fifth(self) -> int: ... # > To define a protocol variable, one can use PEP 526 variable annotations # > in the class body. Additional attributes only defined in the body of a # > method by assignment via self are not allowed. class Template(Protocol): name: str # This is a protocol member value: int = 0 # This one too (with default) def method(self) -> None: self.name = "name" # OK self.temp: list[int] = [] # E: use of self variables not allowed class Concrete: def __init__(self, name: str, value: int) -> None: self.name = name self.value = value def method(self) -> None: return var: Template = Concrete("value", 42) # OK # > To distinguish between protocol class variables and protocol instance # > variables, the special ClassVar annotation should be used as specified # > by PEP 526. By default, protocol variables as defined above are considered # > readable and writable. To define a read-only protocol variable, one can # > use an (abstract) property. class Template2(Protocol): val1: ClassVar[Sequence[int]] class Concrete2_Good1: val1: ClassVar[Sequence[int]] = [2] class Concrete2_Bad1: ... class Concrete2_Bad2: val1: Sequence[float] = [2] class Concrete2_Bad3: val1: list[int] = [2] class Concrete2_Bad4: val1: Sequence[int] = [2] v2_good1: Template2 = Concrete2_Good1() # OK v2_bad1: Template2 = Concrete2_Bad1() # E v2_bad2: Template2 = Concrete2_Bad2() # E v2_bad3: Template2 = Concrete2_Bad3() # E v2_bad4: Template2 = Concrete2_Bad4() # E?: Explicit ClassVar matching is unspecified class Template3(Protocol): val1: Sequence[int] class Concrete3_Good1: val1: Sequence[int] = [0] class Concrete3_Good2: def __init__(self) -> None: self.val1: Sequence[int] = [0] class Concrete3_Bad1: ... class Concrete3_Bad2: val1: ClassVar[Sequence[int]] = [0] class Concrete3_Bad3: @property def val1(self) -> Sequence[int]: return [0] class Concrete3_Bad4: val1: Sequence[float] = [0] class Concrete3_Bad5: val1: list[int] = [0] v3_good1: Template3 = Concrete3_Good1() # OK v3_bad1: Template3 = Concrete3_Bad1() # E v3_bad2: Template3 = Concrete3_Bad2() # E v3_bad3: Template3 = Concrete3_Bad3() # E v3_bad4: Template3 = Concrete3_Bad4() # E v3_bad5: Template3 = Concrete3_Bad5() # E class Template4(Protocol): @property def val1(self) -> Sequence[float]: ... class Concrete4_Good1: @property def val1(self) -> Sequence[float]: return [0] class Concrete4_Good2: @property def val1(self) -> Sequence[int]: return [0] class Concrete4_Good3: val1: Sequence[float] = [0] class Concrete4_Good4: val1: Sequence[int] = [0] class Concrete4_Good5: val1: list[float] = [0] class Concrete4_Good6(NamedTuple): val1: Sequence[float] = [0] @dataclass(frozen=False) class Concrete4_Good7: val1: Sequence[float] = (0,) class Concrete4_Bad1: def val1(self) -> Sequence[int]: # Not a property return [0] class Concrete4_Bad2: ... v4_good1: Template4 = Concrete4_Good1() # OK v4_good2: Template4 = Concrete4_Good2() # OK v4_good3: Template4 = Concrete4_Good3() # OK v4_good4: Template4 = Concrete4_Good4() # OK v4_good5: Template4 = Concrete4_Good5() # OK v4_good6: Template4 = Concrete4_Good6() # OK v4_good7: Template4 = Concrete4_Good7() # OK v4_bad1: Template4 = Concrete4_Bad1() # E v4_bad2: Template4 = Concrete4_Bad2() # E class Template5(Protocol): def method1(self, a: int, b: int) -> float: ... class Concrete5_Good1: def method1(self, a: float, b: float) -> int: return 0 class Concrete5_Good2: def method1(self, *args: float, **kwargs: float) -> Any: return 0.0 class Concrete5_Good3: def method1(self, a, b) -> Any: return 0.0 class Concrete5_Good4: @classmethod def method1(cls, a: int, b: int) -> float: return 0 class Concrete5_Good5: @staticmethod def method1(a: int, b: int) -> float: return 0 class Concrete5_Bad1: def method1(self, a, c) -> int: return 0 class Concrete5_Bad2: def method1(self, a: int, c: int) -> int: return 0 class Concrete5_Bad3: def method1(self, *, a: int, b: int) -> float: return 0 class Concrete5_Bad4: def method1(self, a: int, b: int, /) -> float: return 0 class Concrete5_Bad5: @staticmethod def method1(self, a: int, b: int) -> float: return 0 v5_good1: Template5 = Concrete5_Good1() # OK v5_good2: Template5 = Concrete5_Good2() # OK v5_good3: Template5 = Concrete5_Good3() # OK v5_good4: Template5 = Concrete5_Good4() # OK v5_good5: Template5 = Concrete5_Good5() # OK v5_bad1: Template5 = Concrete5_Bad1() # E v5_bad2: Template5 = Concrete5_Bad2() # E v5_bad3: Template5 = Concrete5_Bad3() # E v5_bad4: Template5 = Concrete5_Bad4() # E v5_bad5: Template5 = Concrete5_Bad5() # E class Template6(Protocol): @property def val1(self) -> Sequence[float]: ... @val1.setter def val1(self, val: Sequence[float]) -> None: ... class Concrete6_Good1: @property def val1(self) -> Sequence[float]: return [0] @val1.setter def val1(self, val: Sequence[float]) -> None: pass class Concrete6_Good2: val1: Sequence[float] = [0] @dataclass(frozen=False) class Concrete6_Good3: val1: Sequence[float] = (0,) class Concrete6_Bad1: @property def val1(self) -> Sequence[float]: return [0] class Concrete6_Bad2(NamedTuple): val1: Sequence[float] = [0] @dataclass(frozen=True) class Concrete6_Bad3: val1: Sequence[float] = (0,) v6_good1: Template6 = Concrete6_Good1() # OK v6_good2: Template6 = Concrete6_Good2() # OK v6_good3: Template6 = Concrete6_Good3() # OK v6_bad1: Template6 = Concrete6_Bad1() # E v6_bad2: Template6 = Concrete6_Bad2() # E: named tuple is immutable v6_bad3: Template6 = Concrete6_Bad3() # E: dataclass is frozen # The specification leaves two possible interpretations of a ClassVar protocol # member. One interpretation requires the implementing attribute to be explicitly # declared with ClassVar. The other interpretation imposes only structural # requirements: the attribute must be readable and writable on the class object # and readable on instances of the class. Both interpretations therefore require # the following assignments to be rejected. class Template7(Protocol): val1: ClassVar[int] class Concrete7_Bad1: def __init__(self) -> None: self.val1: int = 42 class Concrete7Meta(type): val1: int = 42 class Concrete7_Bad2(metaclass=Concrete7Meta): pass v7_bad1: Template7 = Concrete7_Bad1() # E: val1 is not readable on the class object v7_bad2: Template7 = Concrete7_Bad2() # E: val1 is not readable on instances