"""

The typing module: Support for gradual typing as defined by PEP 484.

At large scale, the structure of the module is following:

* Imports and exports, all public names should be explicitly added to __all__.

* Internal helper functions: these should never be used in code outside this module.

* _SpecialForm and its instances (special forms): Any, NoReturn, ClassVar, Union, Optional

* Two classes whose instances can be type arguments in addition to types: ForwardRef and TypeVar

* 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.

* 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.

* Special types: NewType, NamedTuple, TypedDict.

* Wrapper submodules for re and io related types.

"""

from abc import abstractmethod, ABCMeta

import collections

import collections.abc

import contextlib

import functools

import operator

import re as stdlib_re # Avoid confusion with the re we export.

import sys

import types

from types import WrapperDescriptorType, MethodWrapperType, MethodDescriptorType

# Please keep __all__ alphabetized within each category.

__all__ = [

# Super-special typing primitives.

'Any',

'Callable',

'ClassVar',

'Final',

'ForwardRef',

'Generic',

'Literal',

'Optional',

'Protocol',

'Tuple',

'Type',

'TypeVar',

'Union',

# ABCs (from collections.abc).

'AbstractSet', # collections.abc.Set.

'ByteString',

'Container',

'ContextManager',

'Hashable',

'ItemsView',

'Iterable',

'Iterator',

'KeysView',

'Mapping',

'MappingView',

'MutableMapping',

'MutableSequence',

'MutableSet',

'Sequence',

'Sized',

'ValuesView',

'Awaitable',

'AsyncIterator',

'AsyncIterable',

'Coroutine',

'Collection',

'AsyncGenerator',

'AsyncContextManager',

# Structural checks, a.k.a. protocols.

'Reversible',

'SupportsAbs',

'SupportsBytes',

'SupportsComplex',

'SupportsFloat',

'SupportsIndex',

'SupportsInt',

'SupportsRound',

# Concrete collection types.

'ChainMap',

'Counter',

'Deque',

'Dict',

'DefaultDict',

'List',

'OrderedDict',

'Set',

'FrozenSet',

'NamedTuple', # Not really a type.

'TypedDict', # Not really a type.

'Generator',

# One-off things.

'AnyStr',

'cast',

'final',

'get_args',

'get_origin',

'get_type_hints',

'NewType',

'no_type_check',

'no_type_check_decorator',

'NoReturn',

'overload',

'runtime_checkable',

'Text',

'TYPE_CHECKING',

]

# The pseudo-submodules 're' and 'io' are part of the public

# namespace, but excluded from __all__ because they might stomp on

# legitimate imports of those modules.

def _type_check(arg, msg, is_argument=True):

"""Check that the argument is a type, and return it (internal helper).

As a special case, accept None and return type(None) instead. Also wrap strings

into ForwardRef instances. Consider several corner cases, for example plain

special forms like Union are not valid, while Union[int, str] is OK, etc.

The msg argument is a human-readable error message, e.g::

"Union[arg, ...]: arg should be a type."

We append the repr() of the actual value (truncated to 100 chars).

"""

invalid_generic_forms = (Generic, Protocol)

if is_argument:

invalid_generic_forms = invalid_generic_forms + (ClassVar, Final)

if arg is None:

return type(None)

if isinstance(arg, str):

return ForwardRef(arg)

if (isinstance(arg, _GenericAlias) and

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)):

raise TypeError(f"Plain {arg} is not valid as type argument")

if isinstance(arg, (type, TypeVar, ForwardRef)):

return arg

if not callable(arg):

raise TypeError(f"{msg} Got {arg!r:.100}.")

return arg

def _type_repr(obj):

"""Return the repr() of an object, special-casing types (internal helper).

If obj is a type, we return a shorter version than the default

type.__repr__, based on the module and qualified name, which is

typically enough to uniquely identify a type. For everything

else, we fall back on repr(obj).

"""

if isinstance(obj, type):

if obj.__module__ == 'builtins':

return obj.__qualname__

return f'{obj.__module__}.{obj.__qualname__}'

if obj is ...:

return('...')

if isinstance(obj, types.FunctionType):

return obj.__name__

return repr(obj)

def _collect_type_vars(types):

"""Collect all type variable contained in types in order of

first appearance (lexicographic order). For example::

_collect_type_vars((T, List[S, T])) == (T, S)

"""

tvars = []

for t in types:

if isinstance(t, TypeVar) and t not in tvars:

tvars.append(t)

if isinstance(t, _GenericAlias) and not t._special:

tvars.extend([t for t in t.__parameters__ if t not in tvars])

return tuple(tvars)

def _subs_tvars(tp, tvars, subs):

"""Substitute type variables 'tvars' with substitutions 'subs'.

These two must have the same length.

"""

if not isinstance(tp, _GenericAlias):

return tp

new_args = list(tp.__args__)

for a, arg in enumerate(tp.__args__):

if isinstance(arg, TypeVar):

for i, tvar in enumerate(tvars):

if arg == tvar:

new_args[a] = subs[i]

else:

new_args[a] = _subs_tvars(arg, tvars, subs)

if tp.__origin__ is Union:

return Union[tuple(new_args)]

return tp.copy_with(tuple(new_args))

def _check_generic(cls, parameters):

"""Check correct count for parameters of a generic cls (internal helper).

This gives a nice error message in case of count mismatch.

"""

if not cls.__parameters__:

raise TypeError(f"{cls} is not a generic class")

alen = len(parameters)

elen = len(cls.__parameters__)

if alen != elen:

raise TypeError(f"Too {'many' if alen > elen else 'few'} parameters for {cls};"

f" actual {alen}, expected {elen}")

def _remove_dups_flatten(parameters):

"""An internal helper for Union creation and substitution: flatten Unions

among parameters, then remove duplicates.

"""

# Flatten out Union[Union[...], ...].

params = []

for p in parameters:

if isinstance(p, _GenericAlias) and p.__origin__ is Union:

params.extend(p.__args__)

elif isinstance(p, tuple) and len(p) > 0 and p[0] is Union:

params.extend(p[1:])

else:

params.append(p)

# Weed out strict duplicates, preserving the first of each occurrence.

all_params = set(params)

if len(all_params) < len(params):

new_params = []

for t in params:

if t in all_params:

new_params.append(t)

all_params.remove(t)

params = new_params

assert not all_params, all_params

return tuple(params)

_cleanups = []

def _tp_cache(func):

"""Internal wrapper caching __getitem__ of generic types with a fallback to

original function for non-hashable arguments.

"""

cached = functools.lru_cache()(func)

_cleanups.append(cached.cache_clear)

@functools.wraps(func)

def inner(*args, **kwds):

try:

return cached(*args, **kwds)

except TypeError:

pass # All real errors (not unhashable args) are raised below.

return func(*args, **kwds)

return inner

def _eval_type(t, globalns, localns):

"""Evaluate all forward references in the given type t.

For use of globalns and localns see the docstring for get_type_hints().

"""

if isinstance(t, ForwardRef):

return t._evaluate(globalns, localns)

if isinstance(t, _GenericAlias):

ev_args = tuple(_eval_type(a, globalns, localns) for a in t.__args__)

if ev_args == t.__args__:

return t

res = t.copy_with(ev_args)

res._special = t._special

return res

return t

class _Final:

"""Mixin to prohibit subclassing"""

__slots__ = ('__weakref__',)

def __init_subclass__(self, /, *args, **kwds):

if '_root' not in kwds:

raise TypeError("Cannot subclass special typing classes")

class _Immutable:

"""Mixin to indicate that object should not be copied."""

def __copy__(self):

return self

def __deepcopy__(self, memo):

return self

class _SpecialForm(_Final, _Immutable, _root=True):

"""Internal indicator of special typing constructs.

See _doc instance attribute for specific docs.

"""

__slots__ = ('_name', '_doc')

def __new__(cls, *args, **kwds):

"""Constructor.

This only exists to give a better error message in case

someone tries to subclass a special typing object (not a good idea).

"""

if (len(args) == 3 and

isinstance(args[0], str) and

isinstance(args[1], tuple)):

# Close enough.

raise TypeError(f"Cannot subclass {cls!r}")

return super().__new__(cls)

def __init__(self, name, doc):

self._name = name

self._doc = doc

def __eq__(self, other):

if not isinstance(other, _SpecialForm):

return NotImplemented

return self._name == other._name

def __hash__(self):

return hash((self._name,))

def __repr__(self):

return 'typing.' + self._name

def __reduce__(self):

return self._name

def __call__(self, *args, **kwds):

raise TypeError(f"Cannot instantiate {self!r}")

def __instancecheck__(self, obj):

raise TypeError(f"{self} cannot be used with isinstance()")

def __subclasscheck__(self, cls):

raise TypeError(f"{self} cannot be used with issubclass()")

@_tp_cache

def __getitem__(self, parameters):

if self._name in ('ClassVar', 'Final'):

item = _type_check(parameters, f'{self._name} accepts only single type.')

return _GenericAlias(self, (item,))

if self._name == 'Union':

if parameters == ():

raise TypeError("Cannot take a Union of no types.")

if not isinstance(parameters, tuple):

parameters = (parameters,)

msg = "Union[arg, ...]: each arg must be a type."

parameters = tuple(_type_check(p, msg) for p in parameters)

parameters = _remove_dups_flatten(parameters)

if len(parameters) == 1:

return parameters[0]

return _GenericAlias(self, parameters)

if self._name == 'Optional':

arg = _type_check(parameters, "Optional[t] requires a single type.")

return Union[arg, type(None)]

if self._name == 'Literal':

# There is no '_type_check' call because arguments to Literal[...] are

# values, not types.

return _GenericAlias(self, parameters)

raise TypeError(f"{self} is not subscriptable")

Any = _SpecialForm('Any', doc=

"""Special type indicating an unconstrained type.

- Any is compatible with every type.

- Any assumed to have all methods.

- All values assumed to be instances of Any.

Note that all the above statements are true from the point of view of

static type checkers. At runtime, Any should not be used with instance

or class checks.

""")

NoReturn = _SpecialForm('NoReturn', doc=

"""Special type indicating functions that never return.

Example::

from typing import NoReturn

def stop() -> NoReturn:

raise Exception('no way')

This type is invalid in other positions, e.g., ``List[NoReturn]``

will fail in static type checkers.

""")

ClassVar = _SpecialForm('ClassVar', doc=

"""Special type construct to mark class variables.

An annotation wrapped in ClassVar indicates that a given

attribute is intended to be used as a class variable and

should not be set on instances of that class. Usage::

class Starship:

stats: ClassVar[Dict[str, int]] = {} # class variable

damage: int = 10 # instance variable

ClassVar accepts only types and cannot be further subscribed.

Note that ClassVar is not a class itself, and should not

be used with isinstance() or issubclass().

""")

Final = _SpecialForm('Final', doc=

"""Special typing construct to indicate final names to type checkers.

A final name cannot be re-assigned or overridden in a subclass.

For example:

MAX_SIZE: Final = 9000

MAX_SIZE += 1 # Error reported by type checker

class Connection:

TIMEOUT: Final[int] = 10

class FastConnector(Connection):

TIMEOUT = 1 # Error reported by type checker

There is no runtime checking of these properties.

""")

Union = _SpecialForm('Union', doc=

"""Union type; Union[X, Y] means either X or Y.

To define a union, use e.g. Union[int, str]. Details:

- The arguments must be types and there must be at least one.

- None as an argument is a special case and is replaced by

type(None).

- Unions of unions are flattened, e.g.::

Union[Union[int, str], float] == Union[int, str, float]

- Unions of a single argument vanish, e.g.::

Union[int] == int # The constructor actually returns int

- Redundant arguments are skipped, e.g.::

Union[int, str, int] == Union[int, str]

- When comparing unions, the argument order is ignored, e.g.::

Union[int, str] == Union[str, int]

- You cannot subclass or instantiate a union.

- You can use Optional[X] as a shorthand for Union[X, None].

""")

Optional = _SpecialForm('Optional', doc=

"""Optional type.

Optional[X] is equivalent to Union[X, None].

""")

Literal = _SpecialForm('Literal', doc=

"""Special typing form to define literal types (a.k.a. value types).

This form can be used to indicate to type checkers that the corresponding

variable or function parameter has a value equivalent to the provided

literal (or one of several literals):

def validate_simple(data: Any) -> Literal[True]: # always returns True

...

MODE = Literal['r', 'rb', 'w', 'wb']

def open_helper(file: str, mode: MODE) -> str:

...

open_helper('/some/path', 'r') # Passes type check

open_helper('/other/path', 'typo') # Error in type checker

Literal[...] cannot be subclassed. At runtime, an arbitrary value

is allowed as type argument to Literal[...], but type checkers may

impose restrictions.

""")

class ForwardRef(_Final, _root=True):

"""Internal wrapper to hold a forward reference."""

__slots__ = ('__forward_arg__', '__forward_code__',

'__forward_evaluated__', '__forward_value__',

'__forward_is_argument__')

def __init__(self, arg, is_argument=True):

if not isinstance(arg, str):

raise TypeError(f"Forward reference must be a string -- got {arg!r}")

try:

code = compile(arg, '<string>', 'eval')

except SyntaxError:

raise SyntaxError(f"Forward reference must be an expression -- got {arg!r}")

self.__forward_arg__ = arg

self.__forward_code__ = code

self.__forward_evaluated__ = False

self.__forward_value__ = None

self.__forward_is_argument__ = is_argument

def _evaluate(self, globalns, localns):

if not self.__forward_evaluated__ or localns is not globalns:

if globalns is None and localns is None:

globalns = localns = {}

elif globalns is None:

globalns = localns

elif localns is None:

localns = globalns

self.__forward_value__ = _type_check(

eval(self.__forward_code__, globalns, localns),

"Forward references must evaluate to types.",

is_argument=self.__forward_is_argument__)

self.__forward_evaluated__ = True

return self.__forward_value__

def __eq__(self, other):

if not isinstance(other, ForwardRef):

return NotImplemented

if self.__forward_evaluated__ and other.__forward_evaluated__:

return (self.__forward_arg__ == other.__forward_arg__ and

self.__forward_value__ == other.__forward_value__)

return self.__forward_arg__ == other.__forward_arg__

def __hash__(self):

return hash(self.__forward_arg__)

def __repr__(self):

return f'ForwardRef({self.__forward_arg__!r})'

class TypeVar(_Final, _Immutable, _root=True):

"""Type variable.

Usage::

T = TypeVar('T') # Can be anything

A = TypeVar('A', str, bytes) # Must be str or bytes

Type variables exist primarily for the benefit of static type

checkers. They serve as the parameters for generic types as well

as for generic function definitions. See class Generic for more

information on generic types. Generic functions work as follows:

def repeat(x: T, n: int) -> List[T]:

'''Return a list containing n references to x.'''

return [x]*n

def longest(x: A, y: A) -> A:

'''Return the longest of two strings.'''

return x if len(x) >= len(y) else y

The latter example's signature is essentially the overloading

of (str, str) -> str and (bytes, bytes) -> bytes. Also note

that if the arguments are instances of some subclass of str,

the return type is still plain str.

At runtime, isinstance(x, T) and issubclass(C, T) will raise TypeError.

Type variables defined with covariant=True or contravariant=True

can be used to declare covariant or contravariant generic types.

See PEP 484 for more details. By default generic types are invariant

in all type variables.

Type variables can be introspected. e.g.:

T.__name__ == 'T'

T.__constraints__ == ()

T.__covariant__ == False

T.__contravariant__ = False

A.__constraints__ == (str, bytes)

Note that only type variables defined in global scope can be pickled.

"""

__slots__ = ('__name__', '__bound__', '__constraints__',

'__covariant__', '__contravariant__')

def __init__(self, name, *constraints, bound=None,

covariant=False, contravariant=False):

self.__name__ = name

if covariant and contravariant:

raise ValueError("Bivariant types are not supported.")

self.__covariant__ = bool(covariant)

self.__contravariant__ = bool(contravariant)

if constraints and bound is not None:

raise TypeError("Constraints cannot be combined with bound=...")

if constraints and len(constraints) == 1:

raise TypeError("A single constraint is not allowed")

msg = "TypeVar(name, constraint, ...): constraints must be types."

self.__constraints__ = tuple(_type_check(t, msg) for t in constraints)

if bound:

self.__bound__ = _type_check(bound, "Bound must be a type.")

else:

self.__bound__ = None

try:

def_mod = sys._getframe(1).f_globals.get('__name__', '__main__') # for pickling

except (AttributeError, ValueError):

def_mod = None

if def_mod != 'typing':

self.__module__ = def_mod

def __repr__(self):

if self.__covariant__:

prefix = '+'

elif self.__contravariant__:

prefix = '-'

else:

prefix = '~'

return prefix + self.__name__

def __reduce__(self):

return self.__name__

# Special typing constructs Union, Optional, Generic, Callable and Tuple

# use three special attributes for internal bookkeeping of generic types:

# * __parameters__ is a tuple of unique free type parameters of a generic

# type, for example, Dict[T, T].__parameters__ == (T,);

# * __origin__ keeps a reference to a type that was subscripted,

# e.g., Union[T, int].__origin__ == Union, or the non-generic version of

# the type.

# * __args__ is a tuple of all arguments used in subscripting,

# e.g., Dict[T, int].__args__ == (T, int).

# Mapping from non-generic type names that have a generic alias in typing

# but with a different name.

_normalize_alias = {'list': 'List',

'tuple': 'Tuple',

'dict': 'Dict',

'set': 'Set',

'frozenset': 'FrozenSet',

'deque': 'Deque',

'defaultdict': 'DefaultDict',

'type': 'Type',

'Set': 'AbstractSet'}

def _is_dunder(attr):

return attr.startswith('__') and attr.endswith('__')

class _GenericAlias(_Final, _root=True):

"""The central part of internal API.

This represents a generic version of type 'origin' with type arguments 'params'.

There are two kind of these aliases: user defined and special. The special ones

are wrappers around builtin collections and ABCs in collections.abc. These must

have 'name' always set. If 'inst' is False, then the alias can't be instantiated,

this is used by e.g. typing.List and typing.Dict.

"""

def __init__(self, origin, params, *, inst=True, special=False, name=None):

self._inst = inst

self._special = special

if special and name is None:

orig_name = origin.__name__

name = _normalize_alias.get(orig_name, orig_name)

self._name = name

if not isinstance(params, tuple):

params = (params,)

self.__origin__ = origin

self.__args__ = tuple(... if a is _TypingEllipsis else

() if a is _TypingEmpty else

a for a in params)

self.__parameters__ = _collect_type_vars(params)

self.__slots__ = None # This is not documented.

if not name:

self.__module__ = origin.__module__

@_tp_cache

def __getitem__(self, params):

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,)

msg = "Parameters to generic types must be types."

params = tuple(_type_check(p, msg) for p in params)

_check_generic(self, params)

return _subs_tvars(self, self.__parameters__, params)

def copy_with(self, params):

# We don't copy self._special.

return _GenericAlias(self.__origin__, params, name=self._name, inst=self._inst)

def __repr__(self):

if (self._name != 'Callable' or

len(self.__args__) == 2 and self.__args__[0] is Ellipsis):

if self._name:

name = 'typing.' + self._name

else:

name = _type_repr(self.__origin__)

if not self._special:

args = f'[{", ".join([_type_repr(a) for a in self.__args__])}]'

else:

args = ''

return (f'{name}{args}')

if self._special:

return 'typing.Callable'

return (f'typing.Callable'

f'[[{", ".join([_type_repr(a) for a in self.__args__[:-1]])}], '

f'{_type_repr(self.__args__[-1])}]')

def __eq__(self, other):

if not isinstance(other, _GenericAlias):

return NotImplemented

if self.__origin__ != other.__origin__:

return False

if self.__origin__ is Union and other.__origin__ is Union:

return frozenset(self.__args__) == frozenset(other.__args__)

return self.__args__ == other.__args__

def __hash__(self):

if self.__origin__ is Union:

return hash((Union, frozenset(self.__args__)))

return hash((self.__origin__, self.__args__))

def __call__(self, *args, **kwargs):

if not self._inst:

raise TypeError(f"Type {self._name} cannot be instantiated; "

f"use {self._name.lower()}() instead")

result = self.__origin__(*args, **kwargs)

try:

result.__orig_class__ = self

except AttributeError:

pass

return result

def __mro_entries__(self, bases):

if self._name: # generic version of an ABC or built-in class

res = []

if self.__origin__ not in bases:

res.append(self.__origin__)

i = bases.index(self)

if not any(isinstance(b, _GenericAlias) or issubclass(b, Generic)

for b in bases[i+1:]):

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:

return ()

return (self.__origin__,)

def __getattr__(self, attr):

# We are careful for copy and pickle.

# Also for simplicity we just don't relay all dunder names

if '__origin__' in self.__dict__ and not _is_dunder(attr):

return getattr(self.__origin__, attr)

raise AttributeError(attr)

def __setattr__(self, attr, val):

if _is_dunder(attr) or attr in ('_name', '_inst', '_special'):

super().__setattr__(attr, val)

else:

setattr(self.__origin__, attr, val)

def __instancecheck__(self, obj):

return self.__subclasscheck__(type(obj))

def __subclasscheck__(self, cls):

if self._special:

if not isinstance(cls, _GenericAlias):

return issubclass(cls, self.__origin__)

if cls._special:

return issubclass(cls.__origin__, self.__origin__)

raise TypeError("Subscripted generics cannot be used with"

" class and instance checks")

def __reduce__(self):

if self._special:

return self._name

if self._name:

origin = globals()[self._name]

else:

origin = self.__origin__

if (origin is Callable and

not (len(self.__args__) == 2 and self.__args__[0] is Ellipsis)):

args = list(self.__args__[:-1]), self.__args__[-1]

else:

args = tuple(self.__args__)

if len(args) == 1 and not isinstance(args[0], tuple):

args, = args

return operator.getitem, (origin, args)

class _VariadicGenericAlias(_GenericAlias, _root=True):

"""Same as _GenericAlias above but for variadic aliases. Currently,

this is used only by special internal aliases: Tuple and Callable.

"""

def __getitem__(self, params):

if self._name != 'Callable' or not self._special:

return self.__getitem_inner__(params)

if not isinstance(params, tuple) or len(params) != 2:

raise TypeError("Callable must be used as "

"Callable[[arg, ...], result].")

args, result = params

if args is Ellipsis:

params = (Ellipsis, result)

else:

if not isinstance(args, list):

raise TypeError(f"Callable[args, result]: args must be a list."

f" Got {args}")

params = (tuple(args), result)

return self.__getitem_inner__(params)

@_tp_cache

def __getitem_inner__(self, params):

if self.__origin__ is tuple and self._special:

if params == ():

return self.copy_with((_TypingEmpty,))

if not isinstance(params, tuple):

params = (params,)

if len(params) == 2 and params[1] is ...:

msg = "Tuple[t, ...]: t must be a type."

p = _type_check(params[0], msg)

return self.copy_with((p, _TypingEllipsis))

msg = "Tuple[t0, t1, ...]: each t must be a type."

params = tuple(_type_check(p, msg) for p in params)

return self.copy_with(params)

if self.__origin__ is collections.abc.Callable and self._special:

args, result = params

msg = "Callable[args, result]: result must be a type."

result = _type_check(result, msg)

if args is Ellipsis:

return self.copy_with((_TypingEllipsis, result))

msg = "Callable[[arg, ...], result]: each arg must be a type."

args = tuple(_type_check(arg, msg) for arg in args)

params = args + (result,)

return self.copy_with(params)

return super().__getitem__(params)

class Generic:

"""Abstract base class for generic types.

A generic type is typically declared by inheriting from

this class parameterized with one or more type variables.

For example, a generic mapping type might be defined as::

class Mapping(Generic[KT, VT]):

def __getitem__(self, key: KT) -> VT:

...

# Etc.

This class can then be used as follows::

def lookup_name(mapping: Mapping[KT, VT], key: KT, default: VT) -> VT:

try:

return mapping[key]

except KeyError:

return default

"""

__slots__ = ()

_is_protocol = False

def __new__(cls, *args, **kwds):

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)

else:

obj = super().__new__(cls, *args, **kwds)

return obj

@_tp_cache

def __class_getitem__(cls, params):

if not isinstance(params, tuple):

params = (params,)

if not params and cls is not Tuple:

raise TypeError(

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 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(

f"Parameters to {cls.__name__}[...] must all be type variables")

if len(set(params)) != len(params):

raise TypeError(

f"Parameters to {cls.__name__}[...] must all be unique")

else:

# Subscripting a regular Generic subclass.

_check_generic(cls, params)

return _GenericAlias(cls, params)

def __init_subclass__(cls, *args, **kwargs):

super().__init_subclass__(*args, **kwargs)

tvars = []

if '__orig_bases__' in cls.__dict__:

error = Generic in cls.__orig_bases__

else:

error = Generic in cls.__bases__ and cls.__name__ != 'Protocol'

if error:

raise TypeError("Cannot inherit from plain Generic")

if '__orig_bases__' in cls.__dict__:

tvars = _collect_type_vars(cls.__orig_bases__)

# Look for Generic[T1, ..., Tn].

# If found, tvars must be a subset of it.

# If not found, tvars is it.

# Also check for and reject plain Generic,

# and reject multiple Generic[...].

gvars = None

for base in cls.__orig_bases__:

if (isinstance(base, _GenericAlias) and

base.__origin__ is Generic):

if gvars is not None:

raise TypeError(

"Cannot inherit from Generic[...] multiple types.")

gvars = base.__parameters__

if gvars is not None:

tvarset = set(tvars)

gvarset = set(gvars)

if not tvarset <= gvarset:

s_vars = ', '.join(str(t) for t in tvars if t not in gvarset)

s_args = ', '.join(str(g) for g in gvars)

raise TypeError(f"Some type variables ({s_vars}) are"

f" not listed in Generic[{s_args}]")

tvars = gvars

cls.__parameters__ = tuple(tvars)

class _TypingEmpty:

"""Internal placeholder for () or []. Used by TupleMeta and CallableMeta

to allow empty list/tuple in specific places, without allowing them

to sneak in where prohibited.

"""

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 = {

'collections.abc': [

'Callable', 'Awaitable', 'Iterable', 'Iterator', 'AsyncIterable',

'Hashable', 'Sized', 'Container', 'Collection', 'Reversible',