import abc
import collections
import contextlib
import sys
import typing
import collections.abc as collections_abc

# After PEP 560, internal typing API was substantially reworked.
# This is especially important for Protocol class which uses internal APIs
# quite extensivelly.
PEP_560 = sys.version_info[:3] >= (3, 7, 0)

# These are used by Protocol implementation
# We use internal typing helpers here, but this significantly reduces
# code duplication. (Also this is only until Protocol is in typing.)
from typing import Generic, Callable, TypeVar, Tuple
if PEP_560:
    GenericMeta = TypingMeta = type
else:
    from typing import GenericMeta, TypingMeta
OLD_GENERICS = False
try:
    from typing import _type_vars, _next_in_mro, _type_check
except ImportError:
    OLD_GENERICS = True
try:
    from typing import _tp_cache
except ImportError:
    _tp_cache = lambda x: x
try:
    from typing import _TypingEllipsis, _TypingEmpty
except ImportError:
    class _TypingEllipsis: pass
    class _TypingEmpty: pass


# The two functions below are copies of typing internal helpers.
# They are needed by _ProtocolMeta


def _no_slots_copy(dct):
    dict_copy = dict(dct)
    if '__slots__' in dict_copy:
        for slot in dict_copy['__slots__']:
            dict_copy.pop(slot, None)
    return dict_copy


def _check_generic(cls, parameters):
    if not cls.__parameters__:
        raise TypeError("%s is not a generic class" % repr(cls))
    alen = len(parameters)
    elen = len(cls.__parameters__)
    if alen != elen:
        raise TypeError("Too %s parameters for %s; actual %s, expected %s" %
                        ("many" if alen > elen else "few", repr(cls), alen, elen))


if hasattr(typing, '_generic_new'):
    _generic_new = typing._generic_new
else:
    # Note: The '_generic_new(...)' function is used as a part of the
    # process of creating a generic type and was added to the typing module
    # as of Python 3.5.3.
    #
    # We've defined '_generic_new(...)' below to exactly match the behavior
    # implemented in older versions of 'typing' bundled with Python 3.5.0 to
    # 3.5.2. This helps eliminate redundancy when defining collection types
    # like 'Deque' later.
    #
    # See https://github.com/python/typing/pull/308 for more details -- in
    # particular, compare and contrast the definition of types like
    # 'typing.List' before and after the merge.

    def _generic_new(base_cls, cls, *args, **kwargs):
        return base_cls.__new__(cls, *args, **kwargs)

# See https://github.com/python/typing/pull/439
if hasattr(typing, '_geqv'):
    from typing import _geqv
    _geqv_defined = True
else:
    _geqv = None
    _geqv_defined = False

if sys.version_info[:2] >= (3, 6):
    import _collections_abc
    _check_methods_in_mro = _collections_abc._check_methods
else:
    def _check_methods_in_mro(C, *methods):
        mro = C.__mro__
        for method in methods:
            for B in mro:
                if method in B.__dict__:
                    if B.__dict__[method] is None:
                        return NotImplemented
                    break
            else:
                return NotImplemented
        return True


# Please keep __all__ alphabetized within each category.
__all__ = [
    # Super-special typing primitives.
    'ClassVar',
    'Final',
    'Type',

    # ABCs (from collections.abc).
    # The following are added depending on presence
    # of their non-generic counterparts in stdlib:
    # 'Awaitable',
    # 'AsyncIterator',
    # 'AsyncIterable',
    # 'Coroutine',
    # 'AsyncGenerator',
    # 'AsyncContextManager',
    # 'ChainMap',

    # Concrete collection types.
    'ContextManager',
    'Counter',
    'Deque',
    'DefaultDict',

    # One-off things.
    'final',
    'Literal',
    'NewType',
    'overload',
    'Text',
    'TYPE_CHECKING',
]

# Protocols are hard to backport to the original version of typing 3.5.0
HAVE_PROTOCOLS = sys.version_info[:3] != (3, 5, 0)

if HAVE_PROTOCOLS:
    __all__.extend(['Protocol', 'runtime'])

# TODO
if hasattr(typing, 'NoReturn'):
    NoReturn = typing.NoReturn
elif hasattr(typing, '_FinalTypingBase'):
    class _NoReturn(typing._FinalTypingBase, _root=True):
        """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.
        """
        __slots__ = ()

        def __instancecheck__(self, obj):
            raise TypeError("NoReturn cannot be used with isinstance().")

        def __subclasscheck__(self, cls):
            raise TypeError("NoReturn cannot be used with issubclass().")

    NoReturn = _NoReturn(_root=True)
else:
    class _NoReturnMeta(typing.TypingMeta):
        """Metaclass for NoReturn"""
        def __new__(cls, name, bases, namespace, _root=False):
            return super().__new__(cls, name, bases, namespace, _root=_root)

        def __instancecheck__(self, obj):
            raise TypeError("NoReturn cannot be used with isinstance().")

        def __subclasscheck__(self, cls):
            raise TypeError("NoReturn cannot be used with issubclass().")

    class NoReturn(typing.Final, metaclass=_NoReturnMeta, _root=True):
        """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.
        """
        __slots__ = ()


# Some unconstrained type variables.  These are used by the container types.
# (These are not for export.)
T = typing.TypeVar('T')  # Any type.
KT = typing.TypeVar('KT')  # Key type.
VT = typing.TypeVar('VT')  # Value type.
T_co = typing.TypeVar('T_co', covariant=True)  # Any type covariant containers.
V_co = typing.TypeVar('V_co', covariant=True)  # Any type covariant containers.
VT_co = typing.TypeVar('VT_co', covariant=True)  # Value type covariant containers.
T_contra = typing.TypeVar('T_contra', contravariant=True)  # Ditto contravariant.


if hasattr(typing, 'ClassVar'):
    ClassVar = typing.ClassVar
elif hasattr(typing, '_FinalTypingBase'):
    class _ClassVar(typing._FinalTypingBase, _root=True):
        """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().
        """

        __slots__ = ('__type__',)

        def __init__(self, tp=None, **kwds):
            self.__type__ = tp

        def __getitem__(self, item):
            cls = type(self)
            if self.__type__ is None:
                return cls(typing._type_check(item,
                           '{} accepts only single type.'.format(cls.__name__[1:])),
                           _root=True)
            raise TypeError('{} cannot be further subscripted'
                            .format(cls.__name__[1:]))

        def _eval_type(self, globalns, localns):
            new_tp = typing._eval_type(self.__type__, globalns, localns)
            if new_tp == self.__type__:
                return self
            return type(self)(new_tp, _root=True)

        def __repr__(self):
            r = super().__repr__()
            if self.__type__ is not None:
                r += '[{}]'.format(typing._type_repr(self.__type__))
            return r

        def __hash__(self):
            return hash((type(self).__name__, self.__type__))

        def __eq__(self, other):
            if not isinstance(other, _ClassVar):
                return NotImplemented
            if self.__type__ is not None:
                return self.__type__ == other.__type__
            return self is other

    ClassVar = _ClassVar(_root=True)
else:
    class _ClassVarMeta(typing.TypingMeta):
        """Metaclass for ClassVar"""

        def __new__(cls, name, bases, namespace, tp=None, _root=False):
            self = super().__new__(cls, name, bases, namespace, _root=_root)
            if tp is not None:
                self.__type__ = tp
            return self

        def __instancecheck__(self, obj):
            raise TypeError("ClassVar cannot be used with isinstance().")

        def __subclasscheck__(self, cls):
            raise TypeError("ClassVar cannot be used with issubclass().")

        def __getitem__(self, item):
            cls = type(self)
            if self.__type__ is not None:
                raise TypeError('{} cannot be further subscripted'
                                .format(cls.__name__[1:]))

            param = typing._type_check(
                item,
                '{} accepts only single type.'.format(cls.__name__[1:]))
            return cls(self.__name__, self.__bases__,
                       dict(self.__dict__), tp=param, _root=True)

        def _eval_type(self, globalns, localns):
            new_tp = typing._eval_type(self.__type__, globalns, localns)
            if new_tp == self.__type__:
                return self
            return type(self)(self.__name__, self.__bases__,
                              dict(self.__dict__), tp=self.__type__,
                              _root=True)

        def __repr__(self):
            r = super().__repr__()
            if self.__type__ is not None:
                r += '[{}]'.format(typing._type_repr(self.__type__))
            return r

        def __hash__(self):
            return hash((type(self).__name__, self.__type__))

        def __eq__(self, other):
            if not isinstance(other, ClassVar):
                return NotImplemented
            if self.__type__ is not None:
                return self.__type__ == other.__type__
            return self is other

    class ClassVar(typing.Final, metaclass=_ClassVarMeta, _root=True):
        """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().
        """

        __type__ = None

if sys.version_info[:2] >= (3, 7):
    class _FinalForm(typing._SpecialForm, _root=True):

        def __repr__(self):
            return 'typing_extensions.' + self._name

        def __getitem__(self, parameters):
            item = _type_check(parameters,
                               '{} accepts only single type'.format(self._name))
            return _GenericAlias(self, (item,))

    Final = _FinalForm('Final', doc=
        """A special typing construct to indicate that a 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.
        """)
elif hasattr(typing, '_FinalTypingBase'):
    class _Final(typing._FinalTypingBase, _root=True):
        """A special typing construct to indicate that a 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.
        """

        __slots__ = ('__type__',)

        def __init__(self, tp=None, **kwds):
            self.__type__ = tp

        def __getitem__(self, item):
            cls = type(self)
            if self.__type__ is None:
                return cls(typing._type_check(item,
                           '{} accepts only single type.'.format(cls.__name__[1:])),
                           _root=True)
            raise TypeError('{} cannot be further subscripted'
                            .format(cls.__name__[1:]))

        def _eval_type(self, globalns, localns):
            new_tp = typing._eval_type(self.__type__, globalns, localns)
            if new_tp == self.__type__:
                return self
            return type(self)(new_tp, _root=True)

        def __repr__(self):
            r = super().__repr__()
            if self.__type__ is not None:
                r += '[{}]'.format(typing._type_repr(self.__type__))
            return r

        def __hash__(self):
            return hash((type(self).__name__, self.__type__))

        def __eq__(self, other):
            if not isinstance(other, _Final):
                return NotImplemented
            if self.__type__ is not None:
                return self.__type__ == other.__type__
            return self is other

    Final = _Final(_root=True)
else:
    class _FinalMeta(typing.TypingMeta):
        """Metaclass for Final"""

        def __new__(cls, name, bases, namespace, tp=None, _root=False):
            self = super().__new__(cls, name, bases, namespace, _root=_root)
            if tp is not None:
                self.__type__ = tp
            return self

        def __instancecheck__(self, obj):
            raise TypeError("Final cannot be used with isinstance().")

        def __subclasscheck__(self, cls):
            raise TypeError("Final cannot be used with issubclass().")

        def __getitem__(self, item):
            cls = type(self)
            if self.__type__ is not None:
                raise TypeError('{} cannot be further subscripted'
                                .format(cls.__name__[1:]))

            param = typing._type_check(
                item,
                '{} accepts only single type.'.format(cls.__name__[1:]))
            return cls(self.__name__, self.__bases__,
                       dict(self.__dict__), tp=param, _root=True)

        def _eval_type(self, globalns, localns):
            new_tp = typing._eval_type(self.__type__, globalns, localns)
            if new_tp == self.__type__:
                return self
            return type(self)(self.__name__, self.__bases__,
                              dict(self.__dict__), tp=self.__type__,
                              _root=True)

        def __repr__(self):
            r = super().__repr__()
            if self.__type__ is not None:
                r += '[{}]'.format(typing._type_repr(self.__type__))
            return r

        def __hash__(self):
            return hash((type(self).__name__, self.__type__))

        def __eq__(self, other):
            if not isinstance(other, Final):
                return NotImplemented
            if self.__type__ is not None:
                return self.__type__ == other.__type__
            return self is other

    class Final(typing.Final, metaclass=_FinalMeta, _root=True):
        """A special typing construct to indicate that a 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.
        """

        __type__ = None


def final(f):
    """This decorator can be used to indicate to type checkers that
    the decorated method cannot be overridden, and decorated class
    cannot be subclassed. For example:

        class Base:
            @final
            def done(self) -> None:
                ...
        class Sub(Base):
            def done(self) -> None:  # Error reported by type checker
                ...
        @final
        class Leaf:
            ...
        class Other(Leaf):  # Error reported by type checker
            ...

    There is no runtime checking of these properties.
    """
    return f


if hasattr(typing, 'Literal'):
    Literal = typing.Literal 
elif sys.version_info[:2] >= (3, 7):
    class _LiteralForm(typing._SpecialForm, _root=True):

        def __repr__(self):
            return 'typing_extensions.' + self._name

        def __getitem__(self, parameters):
            return _GenericAlias(self, parameters)

    Literal = _LiteralForm('Literal', doc=
        """A type that can be used to indicate to type checkers that the
        corresponding value has a value literally equivalent to the
        provided parameter. For example:

            var: Literal[4] = 4
        
        The type checker understands that 'var' is literally equal to the
        value 4 and no other value.

        Literal[...] cannot be subclassed. There is no runtime checking
        verifying that the parameter is actually a value instead of a type.
        """)
elif hasattr(typing, '_FinalTypingBase'):
    class _Literal(typing._FinalTypingBase, _root=True):
        """A type that can be used to indicate to type checkers that the
        corresponding value has a value literally equivalent to the
        provided parameter. For example:

            var: Literal[4] = 4
        
        The type checker understands that 'var' is literally equal to the
        value 4 and no other value.

        Literal[...] cannot be subclassed. There is no runtime checking
        verifying that the parameter is actually a value instead of a type.
        """

        __slots__ = ('__values__',)

        def __init__(self, values=None, **kwds):
            self.__values__ = values

        def __getitem__(self, values):
            cls = type(self)
            if self.__values__ is None:
                if not isinstance(values, tuple):
                    values = (values,)
                return cls(values, _root=True)
            raise TypeError('{} cannot be further subscripted'
                            .format(cls.__name__[1:]))

        def _eval_type(self, globalns, localns):
            return self

        def __repr__(self):
            r = super().__repr__()
            if self.__values__ is not None:
                r += '[{}]'.format(', '.join(map(typing._type_repr, self.__values__)))
            return r

        def __hash__(self):
            return hash((type(self).__name__, self.__values__))

        def __eq__(self, other):
            if not isinstance(other, _Literal):
                return NotImplemented
            if self.__values__ is not None:
                return self.__values__ == other.__values__
            return self is other

    Literal = _Literal(_root=True)
else:
    class _LiteralMeta(typing.TypingMeta):
        """Metaclass for Literal"""

        def __new__(cls, name, bases, namespace, values=None, _root=False):
            self = super().__new__(cls, name, bases, namespace, _root=_root)
            if values is not None:
                self.__values__ = values
            return self

        def __instancecheck__(self, obj):
            raise TypeError("Literal cannot be used with isinstance().")

        def __subclasscheck__(self, cls):
            raise TypeError("Literal cannot be used with issubclass().")

        def __getitem__(self, item):
            cls = type(self)
            if self.__values__ is not None:
                raise TypeError('{} cannot be further subscripted'
                                .format(cls.__name__[1:]))

            if not isinstance(item, tuple):
                item = (item,)
            return cls(self.__name__, self.__bases__,
                       dict(self.__dict__), values=item, _root=True)

        def _eval_type(self, globalns, localns):
            return self

        def __repr__(self):
            r = super().__repr__()
            if self.__values__ is not None:
                r += '[{}]'.format(', '.join(map(typing._type_repr, self.__values__)))
            return r

        def __hash__(self):
            return hash((type(self).__name__, self.__values__))

        def __eq__(self, other):
            if not isinstance(other, Literal):
                return NotImplemented
            if self.__values__ is not None:
                return self.__values__ == other.__values__
            return self is other

    class Literal(typing.Final, metaclass=_LiteralMeta, _root=True):
        """A type that can be used to indicate to type checkers that the
        corresponding value has a value literally equivalent to the
        provided parameter. For example:

            var: Literal[4] = 4
        
        The type checker understands that 'var' is literally equal to the
        value 4 and no other value.

        Literal[...] cannot be subclassed. There is no runtime checking
        verifying that the parameter is actually a value instead of a type.
        """

        __values__ = None


def _overload_dummy(*args, **kwds):
    """Helper for @overload to raise when called."""
    raise NotImplementedError(
        "You should not call an overloaded function. "
        "A series of @overload-decorated functions "
        "outside a stub module should always be followed "
        "by an implementation that is not @overload-ed.")


def overload(func):
    """Decorator for overloaded functions/methods.

    In a stub file, place two or more stub definitions for the same
    function in a row, each decorated with @overload.  For example:

      @overload
      def utf8(value: None) -> None: ...
      @overload
      def utf8(value: bytes) -> bytes: ...
      @overload
      def utf8(value: str) -> bytes: ...

    In a non-stub file (i.e. a regular .py file), do the same but
    follow it with an implementation.  The implementation should *not*
    be decorated with @overload.  For example:

      @overload
      def utf8(value: None) -> None: ...
      @overload
      def utf8(value: bytes) -> bytes: ...
      @overload
      def utf8(value: str) -> bytes: ...
      def utf8(value):
          # implementation goes here
    """
    return _overload_dummy


# This is not a real generic class.  Don't use outside annotations.
if hasattr(typing, 'Type'):
    Type = typing.Type
else:
    # Internal type variable used for Type[].
    CT_co = typing.TypeVar('CT_co', covariant=True, bound=type)

    class Type(typing.Generic[CT_co], extra=type):
        """A special construct usable to annotate class objects.

        For example, suppose we have the following classes::

          class User: ...  # Abstract base for User classes
          class BasicUser(User): ...
          class ProUser(User): ...
          class TeamUser(User): ...

        And a function that takes a class argument that's a subclass of
        User and returns an instance of the corresponding class::

          U = TypeVar('U', bound=User)
          def new_user(user_class: Type[U]) -> U:
              user = user_class()
              # (Here we could write the user object to a database)
              return user
          joe = new_user(BasicUser)

        At this point the type checker knows that joe has type BasicUser.
        """

        __slots__ = ()


# Various ABCs mimicking those in collections.abc.
# A few are simply re-exported for completeness.

def _define_guard(type_name):
    """
    Returns True if the given type isn't defined in typing but
    is defined in collections_abc.

    Adds the type to __all__ if the collection is found in either
    typing or collection_abc.
    """
    if hasattr(typing, type_name):
        __all__.append(type_name)
        globals()[type_name] = getattr(typing, type_name)
        return False
    elif hasattr(collections_abc, type_name):
        __all__.append(type_name)
        return True
    else:
        return False


class _ExtensionsGenericMeta(GenericMeta):
    def __subclasscheck__(self, subclass):
        """This mimics a more modern GenericMeta.__subclasscheck__() logic
        (that does not have problems with recursion) to work around interactions
        between collections, typing, and typing_extensions on older
        versions of Python, see https://github.com/python/typing/issues/501.
        """
        if sys.version_info[:3] >= (3, 5, 3) or sys.version_info[:3] < (3, 5, 0):
            if self.__origin__ is not None:
                if sys._getframe(1).f_globals['__name__'] not in ['abc', 'functools']:
                    raise TypeError("Parameterized generics cannot be used with class "
                                    "or instance checks")
                return False
        if not self.__extra__:
            return super().__subclasscheck__(subclass)
        res = self.__extra__.__subclasshook__(subclass)
        if res is not NotImplemented:
            return res
        if self.__extra__ in subclass.__mro__:
            return True
        for scls in self.__extra__.__subclasses__():
            if isinstance(scls, GenericMeta):
                continue
            if issubclass(subclass, scls):
                return True
        return False


if _define_guard('Awaitable'):
    class Awaitable(typing.Generic[T_co], metaclass=_ExtensionsGenericMeta,
                    extra=collections_abc.Awaitable):
        __slots__ = ()


if _define_guard('Coroutine'):
    class Coroutine(Awaitable[V_co], typing.Generic[T_co, T_contra, V_co],
                    metaclass=_ExtensionsGenericMeta,
                    extra=collections_abc.Coroutine):
        __slots__ = ()


if _define_guard('AsyncIterable'):
    class AsyncIterable(typing.Generic[T_co],
                        metaclass=_ExtensionsGenericMeta,
                        extra=collections_abc.AsyncIterable):
        __slots__ = ()


if _define_guard('AsyncIterator'):
    class AsyncIterator(AsyncIterable[T_co],
                        metaclass=_ExtensionsGenericMeta,
                        extra=collections_abc.AsyncIterator):
        __slots__ = ()


if hasattr(typing, 'Deque'):
    Deque = typing.Deque
elif _geqv_defined:
    class Deque(collections.deque, typing.MutableSequence[T],
                metaclass=_ExtensionsGenericMeta,
                extra=collections.deque):
        __slots__ = ()

        def __new__(cls, *args, **kwds):
            if _geqv(cls, Deque):
                return collections.deque(*args, **kwds)
            return _generic_new(collections.deque, cls, *args, **kwds)
else:
    class Deque(collections.deque, typing.MutableSequence[T],
                metaclass=_ExtensionsGenericMeta,
                extra=collections.deque):
        __slots__ = ()

        def __new__(cls, *args, **kwds):
            if cls._gorg is Deque:
                return collections.deque(*args, **kwds)
            return _generic_new(collections.deque, cls, *args, **kwds)


if hasattr(typing, 'ContextManager'):
    ContextManager = typing.ContextManager
elif hasattr(contextlib, 'AbstractContextManager'):
    class ContextManager(typing.Generic[T_co],
                         metaclass=_ExtensionsGenericMeta,
                         extra=contextlib.AbstractContextManager):
        __slots__ = ()
else:
    class ContextManager(typing.Generic[T_co]):
        __slots__ = ()

        def __enter__(self):
            return self

        @abc.abstractmethod
        def __exit__(self, exc_type, exc_value, traceback):
            return None

        @classmethod
        def __subclasshook__(cls, C):
            if cls is ContextManager:
                # In Python 3.6+, it is possible to set a method to None to
                # explicitly indicate that the class does not implement an ABC
                # (https://bugs.python.org/issue25958), but we do not support
                # that pattern here because this fallback class is only used
                # in Python 3.5 and earlier.
                if (any("__enter__" in B.__dict__ for B in C.__mro__) and
                    any("__exit__" in B.__dict__ for B in C.__mro__)):
                    return True
            return NotImplemented


if hasattr(typing, 'AsyncContextManager'):
    AsyncContextManager = typing.AsyncContextManager
    __all__.append('AsyncContextManager')
elif hasattr(contextlib, 'AbstractAsyncContextManager'):
    class AsyncContextManager(typing.Generic[T_co],
                              metaclass=_ExtensionsGenericMeta,
                              extra=contextlib.AbstractAsyncContextManager):
        __slots__ = ()

    __all__.append('AsyncContextManager')
elif sys.version_info[:2] >= (3, 5):
    exec("""
class AsyncContextManager(typing.Generic[T_co]):
    __slots__ = ()

    async def __aenter__(self):
        return self

    @abc.abstractmethod
    async def __aexit__(self, exc_type, exc_value, traceback):
        return None

    @classmethod
    def __subclasshook__(cls, C):
        if cls is AsyncContextManager:
            return _check_methods_in_mro(C, "__aenter__", "__aexit__")
        return NotImplemented

__all__.append('AsyncContextManager')
""")


if hasattr(typing, 'DefaultDict'):
    DefaultDict = typing.DefaultDict
elif _geqv_defined:
    class DefaultDict(collections.defaultdict, typing.MutableMapping[KT, VT],
                      metaclass=_ExtensionsGenericMeta,
                      extra=collections.defaultdict):

        __slots__ = ()

        def __new__(cls, *args, **kwds):
            if _geqv(cls, DefaultDict):
                return collections.defaultdict(*args, **kwds)
            return _generic_new(collections.defaultdict, cls, *args, **kwds)
else:
    class DefaultDict(collections.defaultdict, typing.MutableMapping[KT, VT],
                      metaclass=_ExtensionsGenericMeta,
                      extra=collections.defaultdict):

        __slots__ = ()

        def __new__(cls, *args, **kwds):
            if cls._gorg is DefaultDict:
                return collections.defaultdict(*args, **kwds)
            return _generic_new(collections.defaultdict, cls, *args, **kwds)


if hasattr(typing, 'Counter'):
    Counter = typing.Counter
elif (3, 5, 0) <= sys.version_info[:3] <= (3, 5, 1):
    assert _geqv_defined
    _TInt = typing.TypeVar('_TInt')

    class _CounterMeta(typing.GenericMeta):
        """Metaclass for Counter"""
        def __getitem__(self, item):
            return super().__getitem__((item, int))

    class Counter(collections.Counter,
                  typing.Dict[T, int],
                  metaclass=_CounterMeta,
                  extra=collections.Counter):

        __slots__ = ()

        def __new__(cls, *args, **kwds):
            if _geqv(cls, Counter):
                return collections.Counter(*args, **kwds)
            return _generic_new(collections.Counter, cls, *args, **kwds)

elif _geqv_defined:
    class Counter(collections.Counter,
                  typing.Dict[T, int],
                  metaclass=_ExtensionsGenericMeta, extra=collections.Counter):

        __slots__ = ()

        def __new__(cls, *args, **kwds):
            if _geqv(cls, Counter):
                return collections.Counter(*args, **kwds)
            return _generic_new(collections.Counter, cls, *args, **kwds)

else:
    class Counter(collections.Counter,
                  typing.Dict[T, int],
                  metaclass=_ExtensionsGenericMeta, extra=collections.Counter):

        __slots__ = ()

        def __new__(cls, *args, **kwds):
            if cls._gorg is Counter:
                return collections.Counter(*args, **kwds)
            return _generic_new(collections.Counter, cls, *args, **kwds)


if hasattr(typing, 'ChainMap'):
    ChainMap = typing.ChainMap
    __all__.append('ChainMap')
elif hasattr(collections, 'ChainMap'):
    # ChainMap only exists in 3.3+
    if _geqv_defined:
        class ChainMap(collections.ChainMap, typing.MutableMapping[KT, VT],
                       metaclass=_ExtensionsGenericMeta,
                       extra=collections.ChainMap):

            __slots__ = ()

            def __new__(cls, *args, **kwds):
                if _geqv(cls, ChainMap):
                    return collections.ChainMap(*args, **kwds)
                return _generic_new(collections.ChainMap, cls, *args, **kwds)
    else:
        class ChainMap(collections.ChainMap, typing.MutableMapping[KT, VT],
                       metaclass=_ExtensionsGenericMeta,
                       extra=collections.ChainMap):

            __slots__ = ()

            def __new__(cls, *args, **kwds):
                if cls._gorg is ChainMap:
                    return collections.ChainMap(*args, **kwds)
                return _generic_new(collections.ChainMap, cls, *args, **kwds)

    __all__.append('ChainMap')


if _define_guard('AsyncGenerator'):
    class AsyncGenerator(AsyncIterator[T_co], typing.Generic[T_co, T_contra],
                         metaclass=_ExtensionsGenericMeta,
                         extra=collections_abc.AsyncGenerator):
        __slots__ = ()


if hasattr(typing, 'NewType'):
    NewType = typing.NewType
else:
    def NewType(name, tp):
        """NewType creates simple unique types with almost zero
        runtime overhead. NewType(name, tp) is considered a subtype of tp
        by static type checkers. At runtime, NewType(name, tp) returns
        a dummy function that simply returns its argument. Usage::

            UserId = NewType('UserId', int)

            def name_by_id(user_id: UserId) -> str:
                ...

            UserId('user')          # Fails type check

            name_by_id(42)          # Fails type check
            name_by_id(UserId(42))  # OK

            num = UserId(5) + 1     # type: int
        """

        def new_type(x):
            return x

        new_type.__name__ = name
        new_type.__supertype__ = tp
        return new_type


if hasattr(typing, 'Text'):
    Text = typing.Text
else:
    Text = str


if hasattr(typing, 'TYPE_CHECKING'):
    TYPE_CHECKING = typing.TYPE_CHECKING
else:
    # Constant that's True when type checking, but False here.
    TYPE_CHECKING = False


def _gorg(cls):
    """This function exists for compatibility with old typing versions."""
    assert isinstance(cls, GenericMeta)
    if hasattr(cls, '_gorg'):
        return cls._gorg
    while cls.__origin__ is not None:
        cls = cls.__origin__
    return cls


if OLD_GENERICS:
    def _next_in_mro(cls):
        """This function exists for compatibility with old typing versions."""
        next_in_mro = object
        for i, c in enumerate(cls.__mro__[:-1]):
            if isinstance(c, GenericMeta) and _gorg(c) is Generic:
                next_in_mro = cls.__mro__[i + 1]
        return next_in_mro


def _get_protocol_attrs(cls):
    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 (
                    '__abstractmethods__', '__annotations__', '__weakref__',
                    '_is_protocol', '_is_runtime_protocol', '__dict__',
                    '__args__', '__slots__',
                    '__next_in_mro__', '__parameters__', '__origin__',
                    '__orig_bases__', '__extra__', '__tree_hash__',
                    '__doc__', '__subclasshook__', '__init__', '__new__',
                    '__module__', '_MutableMapping__marker', '_gorg')):
                attrs.add(attr)
    return attrs


def _is_callable_members_only(cls):
    return all(callable(getattr(cls, attr, None)) for attr in _get_protocol_attrs(cls))


if HAVE_PROTOCOLS and not PEP_560:
    class _ProtocolMeta(GenericMeta):
        """Internal metaclass for Protocol.

        This exists so Protocol classes can be generic without deriving
        from Generic.
        """
        if not OLD_GENERICS:
            def __new__(cls, name, bases, namespace,
                        tvars=None, args=None, origin=None, extra=None, orig_bases=None):
                # This is just a version copied from GenericMeta.__new__ that
                # includes "Protocol" special treatment. (Comments removed for brevity.)
                assert extra is None  # Protocols should not have extra
                if tvars is not None:
                    assert origin is not None
                    assert all(isinstance(t, TypeVar) for t in tvars), tvars
                else:
                    tvars = _type_vars(bases)
                    gvars = None
                    for base in bases:
                        if base is Generic:
                            raise TypeError("Cannot inherit from plain Generic")
                        if (isinstance(base, GenericMeta) and
                                base.__origin__ in (Generic, Protocol)):
                            if gvars is not None:
                                raise TypeError(
                                    "Cannot inherit from Generic[...] or"
                                    " Protocol[...] multiple times.")
                            gvars = base.__parameters__
                    if gvars is None:
                        gvars = tvars
                    else:
                        tvarset = set(tvars)
                        gvarset = set(gvars)
                        if not tvarset <= gvarset:
                            raise TypeError(
                                "Some type variables (%s) "
                                "are not listed in %s[%s]" %
                                (", ".join(str(t) for t in tvars if t not in gvarset),
                                 "Generic" if any(b.__origin__ is Generic
                                                  for b in bases) else "Protocol",
                                 ", ".join(str(g) for g in gvars)))
                        tvars = gvars

                initial_bases = bases
                if (extra is not None and type(extra) is abc.ABCMeta and
                        extra not in bases):
                    bases = (extra,) + bases
                bases = tuple(_gorg(b) if isinstance(b, GenericMeta) else b
                              for b in bases)
                if any(isinstance(b, GenericMeta) and b is not Generic for b in bases):
                    bases = tuple(b for b in bases if b is not Generic)
                namespace.update({'__origin__': origin, '__extra__': extra})
                self = super(GenericMeta, cls).__new__(cls, name, bases, namespace,
                                                       _root=True)
                super(GenericMeta, self).__setattr__('_gorg',
                                                     self if not origin else
                                                     _gorg(origin))
                self.__parameters__ = tvars
                self.__args__ = tuple(... if a is _TypingEllipsis else
                                      () if a is _TypingEmpty else
                                      a for a in args) if args else None
                self.__next_in_mro__ = _next_in_mro(self)
                if orig_bases is None:
                    self.__orig_bases__ = initial_bases
                elif origin is not None:
                    self._abc_registry = origin._abc_registry
                    self._abc_cache = origin._abc_cache
                if hasattr(self, '_subs_tree'):
                    self.__tree_hash__ = (hash(self._subs_tree()) if origin else
                                          super(GenericMeta, self).__hash__())
                return self

        def __init__(cls, *args, **kwargs):
            super().__init__(*args, **kwargs)
            if not cls.__dict__.get('_is_protocol', None):
                cls._is_protocol = any(b is Protocol or
                                       isinstance(b, _ProtocolMeta) and
                                       b.__origin__ is Protocol
                                       for b in cls.__bases__)
            if cls._is_protocol:
                for base in cls.__mro__[1:]:
                    if not (base in (object, Generic, Callable) or
                            isinstance(base, TypingMeta) and base._is_protocol or
                            isinstance(base, GenericMeta) and
                            base.__origin__ is Generic):
                        raise TypeError('Protocols can only inherit from other'
                                        ' protocols, got %r' % base)

                def _no_init(self, *args, **kwargs):
                    if type(self)._is_protocol:
                        raise TypeError('Protocols cannot be instantiated')
                cls.__init__ = _no_init

            def _proto_hook(other):
                if not cls.__dict__.get('_is_protocol', None):
                    return NotImplemented
                if not isinstance(other, type):
                    # Same error as for issubclass(1, int)
                    raise TypeError('issubclass() arg 1 must be a class')
                for attr in _get_protocol_attrs(cls):
                    for base in other.__mro__:
                        if attr in base.__dict__:
                            if base.__dict__[attr] is None:
                                return NotImplemented
                            break
                        annotations = getattr(base, '__annotations__', {})
                        if (isinstance(annotations, typing.Mapping) and attr in annotations and
                                isinstance(other, _ProtocolMeta) and other._is_protocol):
                            break
                    else:
                        return NotImplemented
                return True
            if '__subclasshook__' not in cls.__dict__:
                cls.__subclasshook__ = _proto_hook

        def __instancecheck__(self, instance):
            # We need this method for situations where attributes are
            # assigned in __init__.
            if ((not getattr(self, '_is_protocol', False) or
                    _is_callable_members_only(self)) and
                    issubclass(instance.__class__, self)):
                return True
            if self._is_protocol:
                if all(hasattr(instance, attr) and
                        (not callable(getattr(self, attr, None)) or
                         getattr(instance, attr) is not None)
                        for attr in _get_protocol_attrs(self)):
                    return True
            return super(GenericMeta, self).__instancecheck__(instance)

        def __subclasscheck__(self, cls):
            if self.__origin__ is not None:
                if sys._getframe(1).f_globals['__name__'] not in ['abc', 'functools']:
                    raise TypeError("Parameterized generics cannot be used with class "
                                    "or instance checks")
                return False
            if (self.__dict__.get('_is_protocol', None) and
                    not self.__dict__.get('_is_runtime_protocol', None)):
                if sys._getframe(1).f_globals['__name__'] in ['abc', 'functools', 'typing']:
                    return False
                raise TypeError("Instance and class checks can only be used with"
                                " @runtime protocols")
            if (self.__dict__.get('_is_runtime_protocol', None) and
                    not _is_callable_members_only(self)):
                if sys._getframe(1).f_globals['__name__'] in ['abc', 'functools', 'typing']:
                    return super(GenericMeta, self).__subclasscheck__(cls)
                raise TypeError("Protocols with non-method members"
                                " don't support issubclass()")
            return super(GenericMeta, self).__subclasscheck__(cls)

        if not OLD_GENERICS:
            @_tp_cache
            def __getitem__(self, params):
                # We also need to copy this from GenericMeta.__getitem__ to get
                # special treatment of "Protocol". (Comments removed for brevity.)
                if not isinstance(params, tuple):
                    params = (params,)
                if not params and _gorg(self) is not Tuple:
                    raise TypeError(
                        "Parameter list to %s[...] cannot be empty" % self.__qualname__)
                msg = "Parameters to generic types must be types."
                params = tuple(_type_check(p, msg) for p in params)
                if self in (Generic, Protocol):
                    if not all(isinstance(p, TypeVar) for p in params):
                        raise TypeError(
                            "Parameters to %r[...] must all be type variables" % self)
                    if len(set(params)) != len(params):
                        raise TypeError(
                            "Parameters to %r[...] must all be unique" % self)
                    tvars = params
                    args = params
                elif self in (Tuple, Callable):
                    tvars = _type_vars(params)
                    args = params
                elif self.__origin__ in (Generic, Protocol):
                    raise TypeError("Cannot subscript already-subscripted %s" %
                                    repr(self))
                else:
                    _check_generic(self, params)
                    tvars = _type_vars(params)
                    args = params

                prepend = (self,) if self.__origin__ is None else ()
                return self.__class__(self.__name__,
                                      prepend + self.__bases__,
                                      _no_slots_copy(self.__dict__),
                                      tvars=tvars,
                                      args=args,
                                      origin=self,
                                      extra=self.__extra__,
                                      orig_bases=self.__orig_bases__)

    class Protocol(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_extensions.runtime act as simple-minded runtime protocol that checks
        only the presence of given attributes, ignoring their type signatures.

        Protocol classes can be generic, they are defined as::

          class GenProto({bases}):
              def meth(self) -> T:
                  ...
        """
        __slots__ = ()
        _is_protocol = True

        def __new__(cls, *args, **kwds):
            if _gorg(cls) is Protocol:
                raise TypeError("Type Protocol cannot be instantiated; "
                                "it can be used only as a base class")
            if OLD_GENERICS:
                return _generic_new(_next_in_mro(cls), cls, *args, **kwds)
            return _generic_new(cls.__next_in_mro__, cls, *args, **kwds)
    if Protocol.__doc__ is not None:
        Protocol.__doc__ = Protocol.__doc__.format(bases="Protocol, Generic[T]" if
                                                   OLD_GENERICS else "Protocol[T]")


elif PEP_560:
    from typing import _type_check, _GenericAlias, _collect_type_vars

    class _ProtocolMeta(abc.ABCMeta):
        # This metaclass is a bit 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
                        (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(metaclass=_ProtocolMeta):
        # There is quite a lot of overlapping code with typing.Generic.
        # Unfortunately it is hard to avoid this while these live in two different modules.
        # The duplicated code will be removed when Protocol is moved to typing.
        """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_extensions.runtime act as simple-minded runtime protocol that checks
        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

        def __new__(cls, *args, **kwds):
            if cls is Protocol:
                raise TypeError("Type Protocol cannot be instantiated; "
                                "it can only be used as a base class")
            return super().__new__(cls)

        @_tp_cache
        def __class_getitem__(cls, params):
            if not isinstance(params, tuple):
                params = (params,)
            if not params and cls is not Tuple:
                raise TypeError(
                    "Parameter list to {}[...] cannot be empty".format(cls.__qualname__))
            msg = "Parameters to generic types must be types."
            params = tuple(_type_check(p, msg) for p in params)
            if cls is Protocol:
                # Generic can only be subscripted with unique type variables.
                if not all(isinstance(p, TypeVar) for p in params):
                    i = 0
                    while isinstance(params[i], TypeVar):
                        i += 1
                    raise TypeError(
                        "Parameters to Protocol[...] must all be type variables."
                        " Parameter {} is {}".format(i + 1, params[i]))
                if len(set(params)) != len(params):
                    raise TypeError(
                        "Parameters to Protocol[...] must all be unique")
            else:
                # Subscripting a regular Generic subclass.
                _check_generic(cls, params)
            return _GenericAlias(cls, params)

        def __init_subclass__(cls, *args, **kwargs):
            tvars = []
            if '__orig_bases__' in cls.__dict__:
                error = Generic in cls.__orig_bases__
            else:
                error = Generic in cls.__bases__
            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] or Protocol[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[...] and/or Protocol[...].
                gvars = None
                for base in cls.__orig_bases__:
                    if (isinstance(base, _GenericAlias) and
                            base.__origin__ in (Generic, Protocol)):
                        # for error messages
                        the_base = 'Generic' if base.__origin__ is Generic else 'Protocol'
                        if gvars is not None:
                            raise TypeError(
                                "Cannot inherit from Generic[...]"
                                " and/or Protocol[...] multiple types.")
                        gvars = base.__parameters__
                if gvars is None:
                    gvars = tvars
                else:
                    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("Some type variables ({}) are"
                                        " not listed in {}[{}]".format(s_vars, the_base, s_args))
                    tvars = gvars
            cls.__parameters__ = tuple(tvars)

            # Determine if this is a protocol or a concrete subclass.
            if not cls.__dict__.get('_is_protocol', None):
                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', None):
                    return NotImplemented
                if not getattr(cls, '_is_runtime_protocol', False):
                    if sys._getframe(2).f_globals['__name__'] in ['abc', 'functools']:
                        return NotImplemented
                    raise TypeError("Instance and class checks can only be used with"
                                    " @runtime protocols")
                if not _is_callable_members_only(cls):
                    if sys._getframe(2).f_globals['__name__'] in ['abc', 'functools']:
                        return NotImplemented
                    raise TypeError("Protocols with non-method members"
                                    " don't support issubclass()")
                if not isinstance(other, type):
                    # Same error as for issubclass(1, int)
                    raise TypeError('issubclass() arg 1 must be a class')
                for attr in _get_protocol_attrs(cls):
                    for base in other.__mro__:
                        if attr in base.__dict__:
                            if base.__dict__[attr] is None:
                                return NotImplemented
                            break
                        annotations = getattr(base, '__annotations__', {})
                        if (isinstance(annotations, typing.Mapping) and attr in annotations and
                                isinstance(other, _ProtocolMeta) 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

            # Check consistency of bases.
            for base in cls.__bases__:
                if not (base in (object, Generic, Callable) or
                        isinstance(base, _ProtocolMeta) and base._is_protocol):
                    raise TypeError('Protocols can only inherit from other'
                                    ' protocols, got %r' % base)

            def _no_init(self, *args, **kwargs):
                if type(self)._is_protocol:
                    raise TypeError('Protocols cannot be instantiated')
            cls.__init__ = _no_init


if HAVE_PROTOCOLS:
    def runtime(cls):
        """Mark a protocol class as a runtime protocol, so that it
        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 the
        one-offs in collections.abc such as Hashable.
        """
        if not isinstance(cls, _ProtocolMeta) or not cls._is_protocol:
            raise TypeError('@runtime can be only applied to protocol classes,'
                            ' got %r' % cls)
        cls._is_runtime_protocol = True
        return cls
