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bpo-37058: PEP 544: Add Protocol to typing module (GH-13585) 

I tried to get rid of the `_ProtocolMeta`, but unfortunately it didn'y work. My idea to return a generic alias from `@runtime_checkable` made runtime protocols unpickleable. I am not sure what is worse (a custom metaclass or having some classes unpickleable), so I decided to stick with the status quo (since there were no complains so far). So essentially this is a copy of the implementation in `typing_extensions` with two modifications:
* Rename `@runtime` to `@runtime_checkable` (plus corresponding updates).
* Allow protocols that extend `collections.abc.Iterable` etc.
This commit is contained in:
Ivan Levkivskyi 2019-05-28 08:40:15 +01:00 committed by GitHub
parent 3880f263d2
commit 74d7f76e2c
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4 changed files with 1053 additions and 119 deletions
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98
Doc/library/typing.rst
View File

@ -17,7 +17,8 @@
--------------
This module supports type hints as specified by :pep:`484` and :pep:`526`.
This module provides runtime support for type hints as specified by
:pep:`484`, :pep:`526`, :pep:`544`, :pep:`586`, :pep:`589`, and :pep:`591`.
The most fundamental support consists of the types :data:`Any`, :data:`Union`,
:data:`Tuple`, :data:`Callable`, :class:`TypeVar`, and
:class:`Generic`. For full specification please see :pep:`484`. For
@ -392,6 +393,48 @@ it as a return value) of a more specialized type is a type error. For example::
Use :class:`object` to indicate that a value could be any type in a typesafe
manner. Use :data:`Any` to indicate that a value is dynamically typed.
Nominal vs structural subtyping
-------------------------------
Initially :pep:`484` defined Python static type system as using
*nominal subtyping*. This means that a class ``A`` is allowed where
a class ``B`` is expected if and only if ``A`` is a subclass of ``B``.
This requirement previously also applied to abstract base classes, such as
:class:`Iterable`. The problem with this approach is that a class had
to be explicitly marked to support them, which is unpythonic and unlike
what one would normally do in idiomatic dynamically typed Python code.
For example, this conforms to the :pep:`484`::
from typing import Sized, Iterable, Iterator
class Bucket(Sized, Iterable[int]):
...
def __len__(self) -> int: ...
def __iter__(self) -> Iterator[int]: ...
:pep:`544` allows to solve this problem by allowing users to write
the above code without explicit base classes in the class definition,
allowing ``Bucket`` to be implicitly considered a subtype of both ``Sized``
and ``Iterable[int]`` by static type checkers. This is known as
*structural subtyping* (or static duck-typing)::
from typing import Iterator, Iterable
class Bucket: # Note: no base classes
...
def __len__(self) -> int: ...
def __iter__(self) -> Iterator[int]: ...
def collect(items: Iterable[int]) -> int: ...
result = collect(Bucket()) # Passes type check
Moreover, by subclassing a special class :class:`Protocol`, a user
can define new custom protocols to fully enjoy structural subtyping
(see examples below).
Classes, functions, and decorators
----------------------------------
@ -459,6 +502,39 @@ The module defines the following classes, functions and decorators:
except KeyError:
return default
.. class:: Protocol(Generic)
Base class for protocol classes. Protocol classes are defined like this::
class Proto(Protocol):
def meth(self) -> int:
...
Such classes are primarily used with static type checkers that recognize
structural subtyping (static duck-typing), for example::
class C:
def meth(self) -> int:
return 0
def func(x: Proto) -> int:
return x.meth()
func(C()) # Passes static type check
See :pep:`544` for details. Protocol classes decorated with
:func:`runtime_checkable` (described later) act as simple-minded runtime
protocols that check only the presence of given attributes, ignoring their
type signatures.
Protocol classes can be generic, for example::
class GenProto(Protocol[T]):
def meth(self) -> T:
...
.. versionadded:: 3.8
.. class:: Type(Generic[CT_co])
A variable annotated with ``C`` may accept a value of type ``C``. In
@ -1033,6 +1109,26 @@ The module defines the following classes, functions and decorators:
Note that returning instances of private classes is not recommended.
It is usually preferable to make such classes public.
.. decorator:: runtime_checkable
Mark a protocol class as a runtime protocol.
Such a protocol can be used with :func:`isinstance` and :func:`issubclass`.
This raises :exc:`TypeError` when applied to a non-protocol class. This
allows a simple-minded structural check, very similar to "one trick ponies"
in :mod:`collections.abc` such as :class:`Iterable`. For example::
@runtime_checkable
class Closable(Protocol):
def close(self): ...
assert isinstance(open('/some/file'), Closable)
**Warning:** this will check only the presence of the required methods,
not their type signatures!
.. versionadded:: 3.8
.. data:: Any
Special type indicating an unconstrained type.

731
Lib/test/test_typing.py
View File

@ -12,8 +12,8 @@ from typing import T, KT, VT # Not in __all__.
from typing import Union, Optional, Literal
from typing import Tuple, List, MutableMapping
from typing import Callable
from typing import Generic, ClassVar, Final, final
from typing import cast
from typing import Generic, ClassVar, Final, final, Protocol
from typing import cast, runtime_checkable
from typing import get_type_hints
from typing import no_type_check, no_type_check_decorator
from typing import Type
@ -24,6 +24,7 @@ from typing import Pattern, Match
import abc
import typing
import weakref
import types
from test import mod_generics_cache
@ -585,7 +586,710 @@ class MySimpleMapping(SimpleMapping[XK, XV]):
return default
class Coordinate(Protocol):
x: int
y: int
@runtime_checkable
class Point(Coordinate, Protocol):
label: str
class MyPoint:
x: int
y: int
label: str
class XAxis(Protocol):
x: int
class YAxis(Protocol):
y: int
@runtime_checkable
class Position(XAxis, YAxis, Protocol):
pass
@runtime_checkable
class Proto(Protocol):
attr: int
def meth(self, arg: str) -> int:
...
class Concrete(Proto):
pass
class Other:
attr: int = 1
def meth(self, arg: str) -> int:
if arg == 'this':
return 1
return 0
class NT(NamedTuple):
x: int
y: int
@runtime_checkable
class HasCallProtocol(Protocol):
__call__: typing.Callable
class ProtocolTests(BaseTestCase):
def test_basic_protocol(self):
@runtime_checkable
class P(Protocol):
def meth(self):
pass
class C: pass
class D:
def meth(self):
pass
def f():
pass
self.assertIsSubclass(D, P)
self.assertIsInstance(D(), P)
self.assertNotIsSubclass(C, P)
self.assertNotIsInstance(C(), P)
self.assertNotIsSubclass(types.FunctionType, P)
self.assertNotIsInstance(f, P)
def test_everything_implements_empty_protocol(self):
@runtime_checkable
class Empty(Protocol):
pass
class C:
pass
def f():
pass
for thing in (object, type, tuple, C, types.FunctionType):
self.assertIsSubclass(thing, Empty)
for thing in (object(), 1, (), typing, f):
self.assertIsInstance(thing, Empty)
def test_function_implements_protocol(self):
def f():
pass
self.assertIsInstance(f, HasCallProtocol)
def test_no_inheritance_from_nominal(self):
class C: pass
class BP(Protocol): pass
with self.assertRaises(TypeError):
class P(C, Protocol):
pass
with self.assertRaises(TypeError):
class P(Protocol, C):
pass
with self.assertRaises(TypeError):
class P(BP, C, Protocol):
pass
class D(BP, C): pass
class E(C, BP): pass
self.assertNotIsInstance(D(), E)
self.assertNotIsInstance(E(), D)
def test_no_instantiation(self):
class P(Protocol): pass
with self.assertRaises(TypeError):
P()
class C(P): pass
self.assertIsInstance(C(), C)
T = TypeVar('T')
class PG(Protocol[T]): pass
with self.assertRaises(TypeError):
PG()
with self.assertRaises(TypeError):
PG[int]()
with self.assertRaises(TypeError):
PG[T]()
class CG(PG[T]): pass
self.assertIsInstance(CG[int](), CG)
def test_cannot_instantiate_abstract(self):
@runtime_checkable
class P(Protocol):
@abc.abstractmethod
def ameth(self) -> int:
raise NotImplementedError
class B(P):
pass
class C(B):
def ameth(self) -> int:
return 26
with self.assertRaises(TypeError):
B()
self.assertIsInstance(C(), P)
def test_subprotocols_extending(self):
class P1(Protocol):
def meth1(self):
pass
@runtime_checkable
class P2(P1, Protocol):
def meth2(self):
pass
class C:
def meth1(self):
pass
def meth2(self):
pass
class C1:
def meth1(self):
pass
class C2:
def meth2(self):
pass
self.assertNotIsInstance(C1(), P2)
self.assertNotIsInstance(C2(), P2)
self.assertNotIsSubclass(C1, P2)
self.assertNotIsSubclass(C2, P2)
self.assertIsInstance(C(), P2)
self.assertIsSubclass(C, P2)
def test_subprotocols_merging(self):
class P1(Protocol):
def meth1(self):
pass
class P2(Protocol):
def meth2(self):
pass
@runtime_checkable
class P(P1, P2, Protocol):
pass
class C:
def meth1(self):
pass
def meth2(self):
pass
class C1:
def meth1(self):
pass
class C2:
def meth2(self):
pass
self.assertNotIsInstance(C1(), P)
self.assertNotIsInstance(C2(), P)
self.assertNotIsSubclass(C1, P)
self.assertNotIsSubclass(C2, P)
self.assertIsInstance(C(), P)
self.assertIsSubclass(C, P)
def test_protocols_issubclass(self):
T = TypeVar('T')
@runtime_checkable
class P(Protocol):
def x(self): ...
@runtime_checkable
class PG(Protocol[T]):
def x(self): ...
class BadP(Protocol):
def x(self): ...
class BadPG(Protocol[T]):
def x(self): ...
class C:
def x(self): ...
self.assertIsSubclass(C, P)
self.assertIsSubclass(C, PG)
self.assertIsSubclass(BadP, PG)
with self.assertRaises(TypeError):
issubclass(C, PG[T])
with self.assertRaises(TypeError):
issubclass(C, PG[C])
with self.assertRaises(TypeError):
issubclass(C, BadP)
with self.assertRaises(TypeError):
issubclass(C, BadPG)
with self.assertRaises(TypeError):
issubclass(P, PG[T])
with self.assertRaises(TypeError):
issubclass(PG, PG[int])
def test_protocols_issubclass_non_callable(self):
class C:
x = 1
@runtime_checkable
class PNonCall(Protocol):
x = 1
with self.assertRaises(TypeError):
issubclass(C, PNonCall)
self.assertIsInstance(C(), PNonCall)
PNonCall.register(C)
with self.assertRaises(TypeError):
issubclass(C, PNonCall)
self.assertIsInstance(C(), PNonCall)
# check that non-protocol subclasses are not affected
class D(PNonCall): ...
self.assertNotIsSubclass(C, D)
self.assertNotIsInstance(C(), D)
D.register(C)
self.assertIsSubclass(C, D)
self.assertIsInstance(C(), D)
with self.assertRaises(TypeError):
issubclass(D, PNonCall)
def test_protocols_isinstance(self):
T = TypeVar('T')
@runtime_checkable
class P(Protocol):
def meth(x): ...
@runtime_checkable
class PG(Protocol[T]):
def meth(x): ...
class BadP(Protocol):
def meth(x): ...
class BadPG(Protocol[T]):
def meth(x): ...
class C:
def meth(x): ...
self.assertIsInstance(C(), P)
self.assertIsInstance(C(), PG)
with self.assertRaises(TypeError):
isinstance(C(), PG[T])
with self.assertRaises(TypeError):
isinstance(C(), PG[C])
with self.assertRaises(TypeError):
isinstance(C(), BadP)
with self.assertRaises(TypeError):
isinstance(C(), BadPG)
def test_protocols_isinstance_py36(self):
class APoint:
def __init__(self, x, y, label):
self.x = x
self.y = y
self.label = label
class BPoint:
label = 'B'
def __init__(self, x, y):
self.x = x
self.y = y
class C:
def __init__(self, attr):
self.attr = attr
def meth(self, arg):
return 0
class Bad: pass
self.assertIsInstance(APoint(1, 2, 'A'), Point)
self.assertIsInstance(BPoint(1, 2), Point)
self.assertNotIsInstance(MyPoint(), Point)
self.assertIsInstance(BPoint(1, 2), Position)
self.assertIsInstance(Other(), Proto)
self.assertIsInstance(Concrete(), Proto)
self.assertIsInstance(C(42), Proto)
self.assertNotIsInstance(Bad(), Proto)
self.assertNotIsInstance(Bad(), Point)
self.assertNotIsInstance(Bad(), Position)
self.assertNotIsInstance(Bad(), Concrete)
self.assertNotIsInstance(Other(), Concrete)
self.assertIsInstance(NT(1, 2), Position)
def test_protocols_isinstance_init(self):
T = TypeVar('T')
@runtime_checkable
class P(Protocol):
x = 1
@runtime_checkable
class PG(Protocol[T]):
x = 1
class C:
def __init__(self, x):
self.x = x
self.assertIsInstance(C(1), P)
self.assertIsInstance(C(1), PG)
def test_protocols_support_register(self):
@runtime_checkable
class P(Protocol):
x = 1
class PM(Protocol):
def meth(self): pass
class D(PM): pass
class C: pass
D.register(C)
P.register(C)
self.assertIsInstance(C(), P)
self.assertIsInstance(C(), D)
def test_none_on_non_callable_doesnt_block_implementation(self):
@runtime_checkable
class P(Protocol):
x = 1
class A:
x = 1
class B(A):
x = None
class C:
def __init__(self):
self.x = None
self.assertIsInstance(B(), P)
self.assertIsInstance(C(), P)
def test_none_on_callable_blocks_implementation(self):
@runtime_checkable
class P(Protocol):
def x(self): ...
class A:
def x(self): ...
class B(A):
x = None
class C:
def __init__(self):
self.x = None
self.assertNotIsInstance(B(), P)
self.assertNotIsInstance(C(), P)
def test_non_protocol_subclasses(self):
class P(Protocol):
x = 1
@runtime_checkable
class PR(Protocol):
def meth(self): pass
class NonP(P):
x = 1
class NonPR(PR): pass
class C:
x = 1
class D:
def meth(self): pass
self.assertNotIsInstance(C(), NonP)
self.assertNotIsInstance(D(), NonPR)
self.assertNotIsSubclass(C, NonP)
self.assertNotIsSubclass(D, NonPR)
self.assertIsInstance(NonPR(), PR)
self.assertIsSubclass(NonPR, PR)
def test_custom_subclasshook(self):
class P(Protocol):
x = 1
class OKClass: pass
class BadClass:
x = 1
class C(P):
@classmethod
def __subclasshook__(cls, other):
return other.__name__.startswith("OK")
self.assertIsInstance(OKClass(), C)
self.assertNotIsInstance(BadClass(), C)
self.assertIsSubclass(OKClass, C)
self.assertNotIsSubclass(BadClass, C)
def test_issubclass_fails_correctly(self):
@runtime_checkable
class P(Protocol):
x = 1
class C: pass
with self.assertRaises(TypeError):
issubclass(C(), P)
def test_defining_generic_protocols(self):
T = TypeVar('T')
S = TypeVar('S')
@runtime_checkable
class PR(Protocol[T, S]):
def meth(self): pass
class P(PR[int, T], Protocol[T]):
y = 1
with self.assertRaises(TypeError):
PR[int]
with self.assertRaises(TypeError):
P[int, str]
with self.assertRaises(TypeError):
PR[int, 1]
with self.assertRaises(TypeError):
PR[int, ClassVar]
class C(PR[int, T]): pass
self.assertIsInstance(C[str](), C)
def test_defining_generic_protocols_old_style(self):
T = TypeVar('T')
S = TypeVar('S')
@runtime_checkable
class PR(Protocol, Generic[T, S]):
def meth(self): pass
class P(PR[int, str], Protocol):
y = 1
with self.assertRaises(TypeError):
issubclass(PR[int, str], PR)
self.assertIsSubclass(P, PR)
with self.assertRaises(TypeError):
PR[int]
with self.assertRaises(TypeError):
PR[int, 1]
class P1(Protocol, Generic[T]):
def bar(self, x: T) -> str: ...
class P2(Generic[T], Protocol):
def bar(self, x: T) -> str: ...
@runtime_checkable
class PSub(P1[str], Protocol):
x = 1
class Test:
x = 1
def bar(self, x: str) -> str:
return x
self.assertIsInstance(Test(), PSub)
with self.assertRaises(TypeError):
PR[int, ClassVar]
def test_init_called(self):
T = TypeVar('T')
class P(Protocol[T]): pass
class C(P[T]):
def __init__(self):
self.test = 'OK'
self.assertEqual(C[int]().test, 'OK')
def test_protocols_bad_subscripts(self):
T = TypeVar('T')
S = TypeVar('S')
with self.assertRaises(TypeError):
class P(Protocol[T, T]): pass
with self.assertRaises(TypeError):
class P(Protocol[int]): pass
with self.assertRaises(TypeError):
class P(Protocol[T], Protocol[S]): pass
with self.assertRaises(TypeError):
class P(typing.Mapping[T, S], Protocol[T]): pass
def test_generic_protocols_repr(self):
T = TypeVar('T')
S = TypeVar('S')
class P(Protocol[T, S]): pass
self.assertTrue(repr(P[T, S]).endswith('P[~T, ~S]'))
self.assertTrue(repr(P[int, str]).endswith('P[int, str]'))
def test_generic_protocols_eq(self):
T = TypeVar('T')
S = TypeVar('S')
class P(Protocol[T, S]): pass
self.assertEqual(P, P)
self.assertEqual(P[int, T], P[int, T])
self.assertEqual(P[T, T][Tuple[T, S]][int, str],
P[Tuple[int, str], Tuple[int, str]])
def test_generic_protocols_special_from_generic(self):
T = TypeVar('T')
class P(Protocol[T]): pass
self.assertEqual(P.__parameters__, (T,))
self.assertEqual(P[int].__parameters__, ())
self.assertEqual(P[int].__args__, (int,))
self.assertIs(P[int].__origin__, P)
def test_generic_protocols_special_from_protocol(self):
@runtime_checkable
class PR(Protocol):
x = 1
class P(Protocol):
def meth(self):
pass
T = TypeVar('T')
class PG(Protocol[T]):
x = 1
def meth(self):
pass
self.assertTrue(P._is_protocol)
self.assertTrue(PR._is_protocol)
self.assertTrue(PG._is_protocol)
self.assertFalse(P._is_runtime_protocol)
self.assertTrue(PR._is_runtime_protocol)
self.assertTrue(PG[int]._is_protocol)
self.assertEqual(typing._get_protocol_attrs(P), {'meth'})
self.assertEqual(typing._get_protocol_attrs(PR), {'x'})
self.assertEqual(frozenset(typing._get_protocol_attrs(PG)),
frozenset({'x', 'meth'}))
def test_no_runtime_deco_on_nominal(self):
with self.assertRaises(TypeError):
@runtime_checkable
class C: pass
class Proto(Protocol):
x = 1
with self.assertRaises(TypeError):
@runtime_checkable
class Concrete(Proto):
pass
def test_none_treated_correctly(self):
@runtime_checkable
class P(Protocol):
x = None # type: int
class B(object): pass
self.assertNotIsInstance(B(), P)
class C:
x = 1
class D:
x = None
self.assertIsInstance(C(), P)
self.assertIsInstance(D(), P)
class CI:
def __init__(self):
self.x = 1
class DI:
def __init__(self):
self.x = None
self.assertIsInstance(C(), P)
self.assertIsInstance(D(), P)
def test_protocols_in_unions(self):
class P(Protocol):
x = None # type: int
Alias = typing.Union[typing.Iterable, P]
Alias2 = typing.Union[P, typing.Iterable]
self.assertEqual(Alias, Alias2)
def test_protocols_pickleable(self):
global P, CP # pickle wants to reference the class by name
T = TypeVar('T')
@runtime_checkable
class P(Protocol[T]):
x = 1
class CP(P[int]):
pass
c = CP()
c.foo = 42
c.bar = 'abc'
for proto in range(pickle.HIGHEST_PROTOCOL + 1):
z = pickle.dumps(c, proto)
x = pickle.loads(z)
self.assertEqual(x.foo, 42)
self.assertEqual(x.bar, 'abc')
self.assertEqual(x.x, 1)
self.assertEqual(x.__dict__, {'foo': 42, 'bar': 'abc'})
s = pickle.dumps(P)
D = pickle.loads(s)
class E:
x = 1
self.assertIsInstance(E(), D)
def test_supports_int(self):
self.assertIsSubclass(int, typing.SupportsInt)
@ -634,9 +1338,8 @@ class ProtocolTests(BaseTestCase):
self.assertIsSubclass(int, typing.SupportsIndex)
self.assertNotIsSubclass(str, typing.SupportsIndex)
def test_protocol_instance_type_error(self):
with self.assertRaises(TypeError):
isinstance(0, typing.SupportsAbs)
def test_bundled_protocol_instance_works(self):
self.assertIsInstance(0, typing.SupportsAbs)
class C1(typing.SupportsInt):
def __int__(self) -> int:
return 42
@ -645,6 +1348,20 @@ class ProtocolTests(BaseTestCase):
c = C2()
self.assertIsInstance(c, C1)
def test_collections_protocols_allowed(self):
@runtime_checkable
class Custom(collections.abc.Iterable, Protocol):
def close(self): ...
class A: pass
class B:
def __iter__(self):
return []
def close(self):
return 0
self.assertIsSubclass(B, Custom)
self.assertNotIsSubclass(A, Custom)
class GenericTests(BaseTestCase):
@ -771,7 +1488,7 @@ class GenericTests(BaseTestCase):
def test_new_repr_bare(self):
T = TypeVar('T')
self.assertEqual(repr(Generic[T]), 'typing.Generic[~T]')
self.assertEqual(repr(typing._Protocol[T]), 'typing._Protocol[~T]')
self.assertEqual(repr(typing.Protocol[T]), 'typing.Protocol[~T]')
class C(typing.Dict[Any, Any]): ...
# this line should just work
repr(C.__mro__)
@ -1067,7 +1784,7 @@ class GenericTests(BaseTestCase):
with self.assertRaises(TypeError):
Tuple[Generic[T]]
with self.assertRaises(TypeError):
List[typing._Protocol]
List[typing.Protocol]
def test_type_erasure_special(self):
T = TypeVar('T')

342
Lib/typing.py
View File

@ -9,8 +9,7 @@ At large scale, the structure of the module is following:
* The core of internal generics API: _GenericAlias and _VariadicGenericAlias, the latter is
currently only used by Tuple and Callable. All subscripted types like X[int], Union[int, str],
etc., are instances of either of these classes.
* The public counterpart of the generics API consists of two classes: Generic and Protocol
(the latter is currently private, but will be made public after PEP 544 acceptance).
* The public counterpart of the generics API consists of two classes: Generic and Protocol.
* Public helper functions: get_type_hints, overload, cast, no_type_check,
no_type_check_decorator.
* Generic aliases for collections.abc ABCs and few additional protocols.
@ -18,7 +17,7 @@ At large scale, the structure of the module is following:
* Wrapper submodules for re and io related types.
"""
from abc import abstractmethod, abstractproperty
from abc import abstractmethod, abstractproperty, ABCMeta
import collections
import collections.abc
import contextlib
@ -39,6 +38,7 @@ __all__ = [
'Generic',
'Literal',
'Optional',
'Protocol',
'Tuple',
'Type',
'TypeVar',
@ -102,6 +102,7 @@ __all__ = [
'no_type_check_decorator',
'NoReturn',
'overload',
'runtime_checkable',
'Text',
'TYPE_CHECKING',
]
@ -123,7 +124,7 @@ def _type_check(arg, msg, is_argument=True):
We append the repr() of the actual value (truncated to 100 chars).
"""
invalid_generic_forms = (Generic, _Protocol)
invalid_generic_forms = (Generic, Protocol)
if is_argument:
invalid_generic_forms = invalid_generic_forms + (ClassVar, Final)
@ -135,7 +136,7 @@ def _type_check(arg, msg, is_argument=True):
arg.__origin__ in invalid_generic_forms):
raise TypeError(f"{arg} is not valid as type argument")
if (isinstance(arg, _SpecialForm) and arg not in (Any, NoReturn) or
arg in (Generic, _Protocol)):
arg in (Generic, Protocol)):
raise TypeError(f"Plain {arg} is not valid as type argument")
if isinstance(arg, (type, TypeVar, ForwardRef)):
return arg
@ -665,8 +666,8 @@ class _GenericAlias(_Final, _root=True):
@_tp_cache
def __getitem__(self, params):
if self.__origin__ in (Generic, _Protocol):
# Can't subscript Generic[...] or _Protocol[...].
if self.__origin__ in (Generic, Protocol):
# Can't subscript Generic[...] or Protocol[...].
raise TypeError(f"Cannot subscript already-subscripted {self}")
if not isinstance(params, tuple):
params = (params,)
@ -733,6 +734,8 @@ class _GenericAlias(_Final, _root=True):
res.append(Generic)
return tuple(res)
if self.__origin__ is Generic:
if Protocol in bases:
return ()
i = bases.index(self)
for b in bases[i+1:]:
if isinstance(b, _GenericAlias) and b is not self:
@ -850,10 +853,11 @@ class Generic:
return default
"""
__slots__ = ()
_is_protocol = False
def __new__(cls, *args, **kwds):
if cls is Generic:
raise TypeError("Type Generic cannot be instantiated; "
if cls in (Generic, Protocol):
raise TypeError(f"Type {cls.__name__} cannot be instantiated; "
"it can be used only as a base class")
if super().__new__ is object.__new__ and cls.__init__ is not object.__init__:
obj = super().__new__(cls)
@ -870,17 +874,14 @@ class Generic:
f"Parameter list to {cls.__qualname__}[...] cannot be empty")
msg = "Parameters to generic types must be types."
params = tuple(_type_check(p, msg) for p in params)
if cls is Generic:
# Generic can only be subscripted with unique type variables.
if cls in (Generic, Protocol):
# Generic and Protocol can only be subscripted with unique type variables.
if not all(isinstance(p, TypeVar) for p in params):
raise TypeError(
"Parameters to Generic[...] must all be type variables")
f"Parameters to {cls.__name__}[...] must all be type variables")
if len(set(params)) != len(params):
raise TypeError(
"Parameters to Generic[...] must all be unique")
elif cls is _Protocol:
# _Protocol is internal at the moment, just skip the check
pass
f"Parameters to {cls.__name__}[...] must all be unique")
else:
# Subscripting a regular Generic subclass.
_check_generic(cls, params)
@ -892,7 +893,7 @@ class Generic:
if '__orig_bases__' in cls.__dict__:
error = Generic in cls.__orig_bases__
else:
error = Generic in cls.__bases__ and cls.__name__ != '_Protocol'
error = Generic in cls.__bases__ and cls.__name__ != 'Protocol'
if error:
raise TypeError("Cannot inherit from plain Generic")
if '__orig_bases__' in cls.__dict__:
@ -910,9 +911,7 @@ class Generic:
raise TypeError(
"Cannot inherit from Generic[...] multiple types.")
gvars = base.__parameters__
if gvars is None:
gvars = tvars
else:
if gvars is not None:
tvarset = set(tvars)
gvarset = set(gvars)
if not tvarset <= gvarset:
@ -935,6 +934,204 @@ class _TypingEllipsis:
"""Internal placeholder for ... (ellipsis)."""
_TYPING_INTERNALS = ['__parameters__', '__orig_bases__', '__orig_class__',
'_is_protocol', '_is_runtime_protocol']
_SPECIAL_NAMES = ['__abstractmethods__', '__annotations__', '__dict__', '__doc__',
'__init__', '__module__', '__new__', '__slots__',
'__subclasshook__', '__weakref__']
# These special attributes will be not collected as protocol members.
EXCLUDED_ATTRIBUTES = _TYPING_INTERNALS + _SPECIAL_NAMES + ['_MutableMapping__marker']
def _get_protocol_attrs(cls):
"""Collect protocol members from a protocol class objects.
This includes names actually defined in the class dictionary, as well
as names that appear in annotations. Special names (above) are skipped.
"""
attrs = set()
for base in cls.__mro__[:-1]: # without object
if base.__name__ in ('Protocol', 'Generic'):
continue
annotations = getattr(base, '__annotations__', {})
for attr in list(base.__dict__.keys()) + list(annotations.keys()):
if not attr.startswith('_abc_') and attr not in EXCLUDED_ATTRIBUTES:
attrs.add(attr)
return attrs
def _is_callable_members_only(cls):
# PEP 544 prohibits using issubclass() with protocols that have non-method members.
return all(callable(getattr(cls, attr, None)) for attr in _get_protocol_attrs(cls))
def _no_init(self, *args, **kwargs):
if type(self)._is_protocol:
raise TypeError('Protocols cannot be instantiated')
def _allow_reckless_class_cheks():
"""Allow instnance and class checks for special stdlib modules.
The abc and functools modules indiscriminately call isinstance() and
issubclass() on the whole MRO of a user class, which may contain protocols.
"""
try:
return sys._getframe(3).f_globals['__name__'] in ['abc', 'functools']
except (AttributeError, ValueError): # For platforms without _getframe().
return True
_PROTO_WHITELIST = ['Callable', 'Awaitable',
'Iterable', 'Iterator', 'AsyncIterable', 'AsyncIterator',
'Hashable', 'Sized', 'Container', 'Collection', 'Reversible',
'ContextManager', 'AsyncContextManager']
class _ProtocolMeta(ABCMeta):
# This metaclass is really unfortunate and exists only because of
# the lack of __instancehook__.
def __instancecheck__(cls, instance):
# We need this method for situations where attributes are
# assigned in __init__.
if ((not getattr(cls, '_is_protocol', False) or
_is_callable_members_only(cls)) and
issubclass(instance.__class__, cls)):
return True
if cls._is_protocol:
if all(hasattr(instance, attr) and
# All *methods* can be blocked by setting them to None.
(not callable(getattr(cls, attr, None)) or
getattr(instance, attr) is not None)
for attr in _get_protocol_attrs(cls)):
return True
return super().__instancecheck__(instance)
class Protocol(Generic, metaclass=_ProtocolMeta):
"""Base class for protocol classes.
Protocol classes are defined as::
class Proto(Protocol):
def meth(self) -> int:
...
Such classes are primarily used with static type checkers that recognize
structural subtyping (static duck-typing), for example::
class C:
def meth(self) -> int:
return 0
def func(x: Proto) -> int:
return x.meth()
func(C()) # Passes static type check
See PEP 544 for details. Protocol classes decorated with
@typing.runtime_checkable act as simple-minded runtime protocols that check
only the presence of given attributes, ignoring their type signatures.
Protocol classes can be generic, they are defined as::
class GenProto(Protocol[T]):
def meth(self) -> T:
...
"""
__slots__ = ()
_is_protocol = True
_is_runtime_protocol = False
def __init_subclass__(cls, *args, **kwargs):
super().__init_subclass__(*args, **kwargs)
# Determine if this is a protocol or a concrete subclass.
if not cls.__dict__.get('_is_protocol', False):
cls._is_protocol = any(b is Protocol for b in cls.__bases__)
# Set (or override) the protocol subclass hook.
def _proto_hook(other):
if not cls.__dict__.get('_is_protocol', False):
return NotImplemented
# First, perform various sanity checks.
if not getattr(cls, '_is_runtime_protocol', False):
if _allow_reckless_class_cheks():
return NotImplemented
raise TypeError("Instance and class checks can only be used with"
" @runtime_checkable protocols")
if not _is_callable_members_only(cls):
if _allow_reckless_class_cheks():
return NotImplemented
raise TypeError("Protocols with non-method members"
" don't support issubclass()")
if not isinstance(other, type):
# Same error message as for issubclass(1, int).
raise TypeError('issubclass() arg 1 must be a class')
# Second, perform the actual structural compatibility check.
for attr in _get_protocol_attrs(cls):
for base in other.__mro__:
# Check if the members appears in the class dictionary...
if attr in base.__dict__:
if base.__dict__[attr] is None:
return NotImplemented
break
# ...or in annotations, if it is a sub-protocol.
annotations = getattr(base, '__annotations__', {})
if (isinstance(annotations, collections.abc.Mapping) and
attr in annotations and
issubclass(other, Generic) and other._is_protocol):
break
else:
return NotImplemented
return True
if '__subclasshook__' not in cls.__dict__:
cls.__subclasshook__ = _proto_hook
# We have nothing more to do for non-protocols...
if not cls._is_protocol:
return
# ... otherwise check consistency of bases, and prohibit instantiation.
for base in cls.__bases__:
if not (base in (object, Generic) or
base.__module__ == 'collections.abc' and base.__name__ in _PROTO_WHITELIST or
issubclass(base, Generic) and base._is_protocol):
raise TypeError('Protocols can only inherit from other'
' protocols, got %r' % base)
cls.__init__ = _no_init
def runtime_checkable(cls):
"""Mark a protocol class as a runtime protocol.
Such protocol can be used with isinstance() and issubclass().
Raise TypeError if applied to a non-protocol class.
This allows a simple-minded structural check very similar to
one trick ponies in collections.abc such as Iterable.
For example::
@runtime_checkable
class Closable(Protocol):
def close(self): ...
assert isinstance(open('/some/file'), Closable)
Warning: this will check only the presence of the required methods,
not their type signatures!
"""
if not issubclass(cls, Generic) or not cls._is_protocol:
raise TypeError('@runtime_checkable can be only applied to protocol classes,'
' got %r' % cls)
cls._is_runtime_protocol = True
return cls
def cast(typ, val):
"""Cast a value to a type.
@ -1159,90 +1356,6 @@ def final(f):
return f
class _ProtocolMeta(type):
"""Internal metaclass for _Protocol.
This exists so _Protocol classes can be generic without deriving
from Generic.
"""
def __instancecheck__(self, obj):
if _Protocol not in self.__bases__:
return super().__instancecheck__(obj)
raise TypeError("Protocols cannot be used with isinstance().")
def __subclasscheck__(self, cls):
if not self._is_protocol:
# No structural checks since this isn't a protocol.
return NotImplemented
if self is _Protocol:
# Every class is a subclass of the empty protocol.
return True
# Find all attributes defined in the protocol.
attrs = self._get_protocol_attrs()
for attr in attrs:
if not any(attr in d.__dict__ for d in cls.__mro__):
return False
return True
def _get_protocol_attrs(self):
# Get all Protocol base classes.
protocol_bases = []
for c in self.__mro__:
if getattr(c, '_is_protocol', False) and c.__name__ != '_Protocol':
protocol_bases.append(c)
# Get attributes included in protocol.
attrs = set()
for base in protocol_bases:
for attr in base.__dict__.keys():
# Include attributes not defined in any non-protocol bases.
for c in self.__mro__:
if (c is not base and attr in c.__dict__ and
not getattr(c, '_is_protocol', False)):
break
else:
if (not attr.startswith('_abc_') and
attr != '__abstractmethods__' and
attr != '__annotations__' and
attr != '__weakref__' and
attr != '_is_protocol' and
attr != '_gorg' and
attr != '__dict__' and
attr != '__args__' and
attr != '__slots__' and
attr != '_get_protocol_attrs' and
attr != '__next_in_mro__' and
attr != '__parameters__' and
attr != '__origin__' and
attr != '__orig_bases__' and
attr != '__extra__' and
attr != '__tree_hash__' and
attr != '__module__'):
attrs.add(attr)
return attrs
class _Protocol(Generic, metaclass=_ProtocolMeta):
"""Internal base class for protocol classes.
This implements a simple-minded structural issubclass check
(similar but more general than the one-offs in collections.abc
such as Hashable).
"""
__slots__ = ()
_is_protocol = True
def __class_getitem__(cls, params):
return super().__class_getitem__(params)
# Some unconstrained type variables. These are used by the container types.
# (These are not for export.)
T = TypeVar('T') # Any type.
@ -1347,7 +1460,8 @@ Type.__doc__ = \
"""
class SupportsInt(_Protocol):
@runtime_checkable
class SupportsInt(Protocol):
__slots__ = ()
@abstractmethod
@ -1355,7 +1469,8 @@ class SupportsInt(_Protocol):
pass
class SupportsFloat(_Protocol):
@runtime_checkable
class SupportsFloat(Protocol):
__slots__ = ()
@abstractmethod
@ -1363,7 +1478,8 @@ class SupportsFloat(_Protocol):
pass
class SupportsComplex(_Protocol):
@runtime_checkable
class SupportsComplex(Protocol):
__slots__ = ()
@abstractmethod
@ -1371,7 +1487,8 @@ class SupportsComplex(_Protocol):
pass
class SupportsBytes(_Protocol):
@runtime_checkable
class SupportsBytes(Protocol):
__slots__ = ()
@abstractmethod
@ -1379,7 +1496,8 @@ class SupportsBytes(_Protocol):
pass
class SupportsIndex(_Protocol):
@runtime_checkable
class SupportsIndex(Protocol):
__slots__ = ()
@abstractmethod
@ -1387,7 +1505,8 @@ class SupportsIndex(_Protocol):
pass
class SupportsAbs(_Protocol[T_co]):
@runtime_checkable
class SupportsAbs(Protocol[T_co]):
__slots__ = ()
@abstractmethod
@ -1395,7 +1514,8 @@ class SupportsAbs(_Protocol[T_co]):
pass
class SupportsRound(_Protocol[T_co]):
@runtime_checkable
class SupportsRound(Protocol[T_co]):
__slots__ = ()
@abstractmethod

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@ -0,0 +1 @@
PEP 544: Add ``Protocol`` and ``@runtime_checkable`` to the ``typing`` module.