"""

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, Never, ClassVar, Union, Optional, Concatenate, Unpack

* Classes whose instances can be type arguments in addition to types:

ForwardRef, TypeVar and ParamSpec

* 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

from collections import defaultdict

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

import warnings

from types import WrapperDescriptorType, MethodWrapperType, MethodDescriptorType, GenericAlias

try:

from _typing import _idfunc

except ImportError:

def _idfunc(_, x):

return x

# Please keep __all__ alphabetized within each category.

__all__ = [

# Super-special typing primitives.

'Annotated',

'Any',

'Callable',

'ClassVar',

'Concatenate',

'Final',

'ForwardRef',

'Generic',

'Literal',

'Optional',

'ParamSpec',

'Protocol',

'Tuple',

'Type',

'TypeVar',

'TypeVarTuple',

'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',

# Other concrete types.

'BinaryIO',

'IO',

'Match',

'Pattern',

'TextIO',

# One-off things.

'AnyStr',

'assert_type',

'assert_never',

'cast',

'clear_overloads',

'dataclass_transform',

'final',

'get_args',

'get_origin',

'get_overloads',

'get_type_hints',

'is_typeddict',

'LiteralString',

'Never',

'NewType',

'no_type_check',

'no_type_check_decorator',

'NoReturn',

'NotRequired',

'overload',

'override',

'ParamSpecArgs',

'ParamSpecKwargs',

'Required',

'reveal_type',

'runtime_checkable',

'Self',

'Text',

'TYPE_CHECKING',

'TypeAlias',

'TypeGuard',

'Unpack',

]

# 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_convert(arg, module=None, *, allow_special_forms=False):

"""For converting None to type(None), and strings to ForwardRef."""

if arg is None:

return type(None)

if isinstance(arg, str):

return ForwardRef(arg, module=module, is_class=allow_special_forms)

return arg

def _type_check(arg, msg, is_argument=True, module=None, *, allow_special_forms=False):

"""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 not allow_special_forms:

invalid_generic_forms += (ClassVar,)

if is_argument:

invalid_generic_forms += (Final,)

arg = _type_convert(arg, module=module, allow_special_forms=allow_special_forms)

if (isinstance(arg, _GenericAlias) and

arg.__origin__ in invalid_generic_forms):

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

if arg in (Any, LiteralString, NoReturn, Never, Self, TypeAlias):

return arg

if allow_special_forms and arg in (ClassVar, Final):

return arg

if isinstance(arg, _SpecialForm) or arg in (Generic, Protocol):

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

if type(arg) is tuple:

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

return arg

def _is_param_expr(arg):

return arg is ... or isinstance(arg,

(tuple, list, ParamSpec, _ConcatenateGenericAlias))

def _should_unflatten_callable_args(typ, args):

"""Internal helper for munging collections.abc.Callable's __args__.

The canonical representation for a Callable's __args__ flattens the

argument types, see https://bugs.python.org/issue42195. For example:

collections.abc.Callable[[int, int], str].__args__ == (int, int, str)

collections.abc.Callable[ParamSpec, str].__args__ == (ParamSpec, str)

As a result, if we need to reconstruct the Callable from its __args__,

we need to unflatten it.

"""

return (

typ.__origin__ is collections.abc.Callable

and not (len(args) == 2 and _is_param_expr(args[0]))

)

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).

"""

# When changing this function, don't forget about

# `_collections_abc._type_repr`, which does the same thing

# and must be consistent with this one.

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__

if isinstance(obj, tuple):

# Special case for `repr` of types with `ParamSpec`:

return '[' + ', '.join(_type_repr(t) for t in obj) + ']'

return repr(obj)

def _collect_parameters(args):

"""Collect all type variables and parameter specifications in args

in order of first appearance (lexicographic order). For example::

_collect_parameters((T, Callable[P, T])) == (T, P)

"""

parameters = []

for t in args:

if isinstance(t, type):

# We don't want __parameters__ descriptor of a bare Python class.

pass

elif isinstance(t, tuple):

# `t` might be a tuple, when `ParamSpec` is substituted with

# `[T, int]`, or `[int, *Ts]`, etc.

for x in t:

for collected in _collect_parameters([x]):

if collected not in parameters:

parameters.append(collected)

elif hasattr(t, '__typing_subst__'):

if t not in parameters:

parameters.append(t)

else:

for x in getattr(t, '__parameters__', ()):

if x not in parameters:

parameters.append(x)

return tuple(parameters)

def _check_generic(cls, parameters, elen):

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

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

"""

if not elen:

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

alen = len(parameters)

if alen != elen:

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

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

def _unpack_args(args):

newargs = []

for arg in args:

subargs = getattr(arg, '__typing_unpacked_tuple_args__', None)

if subargs is not None and not (subargs and subargs[-1] is ...):

newargs.extend(subargs)

else:

newargs.append(arg)

return newargs

def _deduplicate(params):

# 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 params

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, (_UnionGenericAlias, types.UnionType)):

params.extend(p.__args__)

else:

params.append(p)

return tuple(_deduplicate(params))

def _flatten_literal_params(parameters):

"""An internal helper for Literal creation: flatten Literals among parameters"""

params = []

for p in parameters:

if isinstance(p, _LiteralGenericAlias):

params.extend(p.__args__)

else:

params.append(p)

return tuple(params)

_cleanups = []

_caches = {}

def _tp_cache(func=None, /, *, typed=False):

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

original function for non-hashable arguments.

"""

def decorator(func):

# The callback 'inner' references the newly created lru_cache

# indirectly by performing a lookup in the global '_caches' dictionary.

# This breaks a reference that can be problematic when combined with

# C API extensions that leak references to types. See GH-98253.

cache = functools.lru_cache(typed=typed)(func)

_caches[func] = cache

_cleanups.append(cache.cache_clear)

del cache

@functools.wraps(func)

def inner(*args, **kwds):

try:

return _caches[func](*args, **kwds)

except TypeError:

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

return func(*args, **kwds)

return inner

if func is not None:

return decorator(func)

return decorator

def _eval_type(t, globalns, localns, recursive_guard=frozenset()):

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

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

recursive_guard is used to prevent infinite recursion with a recursive

ForwardRef.

"""

if isinstance(t, ForwardRef):

return t._evaluate(globalns, localns, recursive_guard)

if isinstance(t, (_GenericAlias, GenericAlias, types.UnionType)):

if isinstance(t, GenericAlias):

args = tuple(

ForwardRef(arg) if isinstance(arg, str) else arg

for arg in t.__args__

)

is_unpacked = t.__unpacked__

if _should_unflatten_callable_args(t, args):

t = t.__origin__[(args[:-1], args[-1])]

else:

t = t.__origin__[args]

if is_unpacked:

t = Unpack[t]

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

if ev_args == t.__args__:

return t

if isinstance(t, GenericAlias):

return GenericAlias(t.__origin__, ev_args)

if isinstance(t, types.UnionType):

return functools.reduce(operator.or_, ev_args)

else:

return t.copy_with(ev_args)

return t

class _Final:

"""Mixin to prohibit subclassing"""

__slots__ = ('__weakref__',)

def __init_subclass__(cls, /, *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."""

__slots__ = ()

def __copy__(self):

return self

def __deepcopy__(self, memo):

return self

class _NotIterable:

"""Mixin to prevent iteration, without being compatible with Iterable.

That is, we could do:

def __iter__(self): raise TypeError()

But this would make users of this mixin duck type-compatible with

collections.abc.Iterable - isinstance(foo, Iterable) would be True.

Luckily, we can instead prevent iteration by setting __iter__ to None, which

is treated specially.

"""

__slots__ = ()

__iter__ = None

# Internal indicator of special typing constructs.

# See __doc__ instance attribute for specific docs.

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

__slots__ = ('_name', '__doc__', '_getitem')

def __init__(self, getitem):

self._getitem = getitem

self._name = getitem.__name__

self.__doc__ = getitem.__doc__

def __getattr__(self, item):

if item in {'__name__', '__qualname__'}:

return self._name

raise AttributeError(item)

def __mro_entries__(self, bases):

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

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 __or__(self, other):

return Union[self, other]

def __ror__(self, other):

return Union[other, self]

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):

return self._getitem(self, parameters)

class _LiteralSpecialForm(_SpecialForm, _root=True):

def __getitem__(self, parameters):

if not isinstance(parameters, tuple):

parameters = (parameters,)

return self._getitem(self, *parameters)

class _AnyMeta(type):

def __instancecheck__(self, obj):

if self is Any:

raise TypeError("typing.Any cannot be used with isinstance()")

return super().__instancecheck__(obj)

def __repr__(self):

if self is Any:

return "typing.Any"

return super().__repr__() # respect to subclasses

class Any(metaclass=_AnyMeta):

"""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

checks.

"""

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

if cls is Any:

raise TypeError("Any cannot be instantiated")

return super().__new__(cls, *args, **kwargs)

@_SpecialForm

def NoReturn(self, parameters):

"""Special type indicating functions that never return.

Example::

from typing import NoReturn

def stop() -> NoReturn:

raise Exception('no way')

NoReturn can also be used as a bottom type, a type that

has no values. Starting in Python 3.11, the Never type should

be used for this concept instead. Type checkers should treat the two

equivalently.

"""

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

# This is semantically identical to NoReturn, but it is implemented

# separately so that type checkers can distinguish between the two

# if they want.

@_SpecialForm

def Never(self, parameters):

"""The bottom type, a type that has no members.

This can be used to define a function that should never be

called, or a function that never returns::

from typing import Never

def never_call_me(arg: Never) -> None:

pass

def int_or_str(arg: int | str) -> None:

never_call_me(arg) # type checker error

match arg:

case int():

print("It's an int")

case str():

print("It's a str")

case _:

never_call_me(arg) # ok, arg is of type Never

"""

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

@_SpecialForm

def Self(self, parameters):

"""Used to spell the type of "self" in classes.

Example::

from typing import Self

class Foo:

def return_self(self) -> Self:

...

return self

This is especially useful for:

- classmethods that are used as alternative constructors

- annotating an `__enter__` method which returns self

"""

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

@_SpecialForm

def LiteralString(self, parameters):

"""Represents an arbitrary literal string.

Example::

from typing import LiteralString

def run_query(sql: LiteralString) -> ...

...

def caller(arbitrary_string: str, literal_string: LiteralString) -> None:

run_query("SELECT * FROM students") # ok

run_query(literal_string) # ok

run_query("SELECT * FROM " + literal_string) # ok

run_query(arbitrary_string) # type checker error

run_query( # type checker error

f"SELECT * FROM students WHERE name = {arbitrary_string}"

)

Only string literals and other LiteralStrings are compatible

with LiteralString. This provides a tool to help prevent

security issues such as SQL injection.

"""

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

@_SpecialForm

def ClassVar(self, parameters):

"""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().

"""

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

return _GenericAlias(self, (item,))

@_SpecialForm

def Final(self, parameters):

"""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.

"""

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

return _GenericAlias(self, (item,))

@_SpecialForm

def Union(self, parameters):

"""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].

"""

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]

if len(parameters) == 2 and type(None) in parameters:

return _UnionGenericAlias(self, parameters, name="Optional")

return _UnionGenericAlias(self, parameters)

@_SpecialForm

def Optional(self, parameters):

"""Optional type.

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

"""

arg = _type_check(parameters, f"{self} requires a single type.")

return Union[arg, type(None)]

@_LiteralSpecialForm

@_tp_cache(typed=True)

def Literal(self, *parameters):

"""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.

"""

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

# values, not types.

parameters = _flatten_literal_params(parameters)

try:

parameters = tuple(p for p, _ in _deduplicate(list(_value_and_type_iter(parameters))))

except TypeError: # unhashable parameters

pass

return _LiteralGenericAlias(self, parameters)

@_SpecialForm

def TypeAlias(self, parameters):

"""Special marker indicating that an assignment should

be recognized as a proper type alias definition by type

checkers.

For example::

Predicate: TypeAlias = Callable[..., bool]

It's invalid when used anywhere except as in the example above.

"""

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

@_SpecialForm

def Concatenate(self, parameters):

"""Used in conjunction with ``ParamSpec`` and ``Callable`` to represent a

higher order function which adds, removes or transforms parameters of a

callable.

For example::

Callable[Concatenate[int, P], int]

See PEP 612 for detailed information.

"""

if parameters == ():

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

if not isinstance(parameters, tuple):

parameters = (parameters,)

if not (parameters[-1] is ... or isinstance(parameters[-1], ParamSpec)):

raise TypeError("The last parameter to Concatenate should be a "

"ParamSpec variable or ellipsis.")

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

parameters = (*(_type_check(p, msg) for p in parameters[:-1]), parameters[-1])

return _ConcatenateGenericAlias(self, parameters,

_paramspec_tvars=True)

@_SpecialForm

def TypeGuard(self, parameters):

"""Special typing form used to annotate the return type of a user-defined

type guard function. ``TypeGuard`` only accepts a single type argument.

At runtime, functions marked this way should return a boolean.

``TypeGuard`` aims to benefit *type narrowing* -- a technique used by static

type checkers to determine a more precise type of an expression within a

program's code flow. Usually type narrowing is done by analyzing

conditional code flow and applying the narrowing to a block of code. The

conditional expression here is sometimes referred to as a "type guard".

Sometimes it would be convenient to use a user-defined boolean function

as a type guard. Such a function should use ``TypeGuard[...]`` as its

return type to alert static type checkers to this intention.

Using ``-> TypeGuard`` tells the static type checker that for a given

function:

1. The return value is a boolean.

2. If the return value is ``True``, the type of its argument

is the type inside ``TypeGuard``.

For example::

def is_str(val: Union[str, float]):

# "isinstance" type guard

if isinstance(val, str):

# Type of ``val`` is narrowed to ``str``

...

else:

# Else, type of ``val`` is narrowed to ``float``.

...

Strict type narrowing is not enforced -- ``TypeB`` need not be a narrower

form of ``TypeA`` (it can even be a wider form) and this may lead to

type-unsafe results. The main reason is to allow for things like

narrowing ``List[object]`` to ``List[str]`` even though the latter is not

a subtype of the former, since ``List`` is invariant. The responsibility of

writing type-safe type guards is left to the user.

``TypeGuard`` also works with type variables. For more information, see

PEP 647 (User-Defined Type Guards).

"""

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

return _GenericAlias(self, (item,))

class ForwardRef(_Final, _root=True):

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

__slots__ = ('__forward_arg__', '__forward_code__',

'__forward_evaluated__', '__forward_value__',

'__forward_is_argument__', '__forward_is_class__',

'__forward_module__')

def __init__(self, arg, is_argument=True, module=None, *, is_class=False):

if not isinstance(arg, str):

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

# If we do `def f(*args: *Ts)`, then we'll have `arg = '*Ts'`.

# Unfortunately, this isn't a valid expression on its own, so we

# do the unpacking manually.

if arg[0] == '*':

arg_to_compile = f'({arg},)[0]' # E.g. (*Ts,)[0] or (*tuple[int, int],)[0]

else:

arg_to_compile = arg

try:

code = compile(arg_to_compile, '<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

self.__forward_is_class__ = is_class

self.__forward_module__ = module

def _evaluate(self, globalns, localns, recursive_guard):

if self.__forward_arg__ in recursive_guard:

return self

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

if self.__forward_module__ is not None:

globalns = getattr(

sys.modules.get(self.__forward_module__, None), '__dict__', globalns

)

type_ = _type_check(

eval(self.__forward_code__, globalns, localns),

"Forward references must evaluate to types.",

is_argument=self.__forward_is_argument__,

allow_special_forms=self.__forward_is_class__,

)

self.__forward_value__ = _eval_type(

type_, globalns, localns, recursive_guard | {self.__forward_arg__}

)

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__ and

self.__forward_module__ == other.__forward_module__)

def __hash__(self):

return hash((self.__forward_arg__, self.__forward_module__))

def __or__(self, other):

return Union[self, other]

def __ror__(self, other):

return Union[other, self]

def __repr__(self):

if self.__forward_module__ is None:

module_repr = ''

else:

module_repr = f', module={self.__forward_module__!r}'

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

def _is_unpacked_typevartuple(x: Any) -> bool:

return ((not isinstance(x, type)) and

getattr(x, '__typing_is_unpacked_typevartuple__', False))

def _is_typevar_like(x: Any) -> bool:

return isinstance(x, (TypeVar, ParamSpec)) or _is_unpacked_typevartuple(x)

class _PickleUsingNameMixin:

"""Mixin enabling pickling based on self.__name__."""

def __reduce__(self):

return self.__name__

class _BoundVarianceMixin:

"""Mixin giving __init__ bound and variance arguments.

This is used by TypeVar and ParamSpec, which both employ the notions of

a type 'bound' (restricting type arguments to be a subtype of some

specified type) and type 'variance' (determining subtype relations between

generic types).

"""

def __init__(self, bound, covariant, contravariant):

"""Used to setup TypeVars and ParamSpec's bound, covariant and

contravariant attributes.

"""

if covariant and contravariant:

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

self.__covariant__ = bool(covariant)

self.__contravariant__ = bool(contravariant)

if bound:

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

else:

self.__bound__ = None

def __or__(self, right):

return Union[self, right]

def __ror__(self, left):

return Union[left, self]

def __repr__(self):

if self.__covariant__:

prefix = '+'

elif self.__contravariant__:

prefix = '-'

else:

prefix = '~'

return prefix + self.__name__

def __mro_entries__(self, bases):

raise TypeError(f"Cannot subclass an instance of {type(self).__name__}")

class TypeVar(_Final, _Immutable, _BoundVarianceMixin, _PickleUsingNameMixin,

_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.