--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.7/site-packages/typing_extensions.py	Sat May 02 07:14:21 2020 -0400
@@ -0,0 +1,2058 @@
+import abc
+import collections
+import contextlib
+import sys
+import typing
+import collections.abc as collections_abc
+import operator
+
+# 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
+
+# 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)
+
+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 _subs_tree  # noqa
+    SUBS_TREE = True
+except ImportError:
+    SUBS_TREE = False
+try:
+    from typing import _tp_cache
+except ImportError:
+    def _tp_cache(x):
+        return 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',
+    'TypedDict',
+
+    # One-off things.
+    'final',
+    'IntVar',
+    'Literal',
+    'NewType',
+    'overload',
+    'Text',
+    'TYPE_CHECKING',
+]
+
+# Annotated relies on substitution trees of pep 560. It will not work for
+# versions of typing older than 3.5.3
+HAVE_ANNOTATED = PEP_560 or SUBS_TREE
+
+if PEP_560:
+    __all__.extend(["get_args", "get_origin", "get_type_hints"])
+
+if HAVE_ANNOTATED:
+    __all__.append("Annotated")
+
+# 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', 'runtime_checkable'])
+
+
+# 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
+
+# On older versions of typing there is an internal class named "Final".
+if hasattr(typing, 'Final') and sys.version_info[:2] >= (3, 7):
+    Final = typing.Final
+elif 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 = typing._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
+
+
+if hasattr(typing, 'final'):
+    final = typing.final
+else:
+    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
+
+
+def IntVar(name):
+    return TypeVar(name)
+
+
+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):  # noqa
+        """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
+
+
+_PROTO_WHITELIST = ['Callable', 'Awaitable',
+                    'Iterable', 'Iterator', 'AsyncIterable', 'AsyncIterator',
+                    'Hashable', 'Sized', 'Container', 'Collection', 'Reversible',
+                    'ContextManager', 'AsyncContextManager']
+
+
+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 hasattr(typing, 'Protocol'):
+    Protocol = typing.Protocol
+elif 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) or
+                            base.__module__ == 'collections.abc' and
+                            base.__name__ in _PROTO_WHITELIST 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  # noqa
+
+    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) or
+                        base.__module__ == 'collections.abc' and
+                        base.__name__ in _PROTO_WHITELIST 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 hasattr(typing, 'runtime_checkable'):
+    runtime_checkable = typing.runtime_checkable
+elif HAVE_PROTOCOLS:
+    def runtime_checkable(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_checkable can be only applied to protocol classes,'
+                            ' got %r' % cls)
+        cls._is_runtime_protocol = True
+        return cls
+
+
+if HAVE_PROTOCOLS:
+    # Exists for backwards compatibility.
+    runtime = runtime_checkable
+
+
+if sys.version_info[:2] >= (3, 9):
+    # The standard library TypedDict in Python 3.8 does not store runtime information
+    # about which (if any) keys are optional.  See https://bugs.python.org/issue38834
+    TypedDict = typing.TypedDict
+else:
+    def _check_fails(cls, other):
+        try:
+            if sys._getframe(1).f_globals['__name__'] not in ['abc',
+                                                              'functools',
+                                                              'typing']:
+                # Typed dicts are only for static structural subtyping.
+                raise TypeError('TypedDict does not support instance and class checks')
+        except (AttributeError, ValueError):
+            pass
+        return False
+
+    def _dict_new(*args, **kwargs):
+        if not args:
+            raise TypeError('TypedDict.__new__(): not enough arguments')
+        _, args = args[0], args[1:]  # allow the "cls" keyword be passed
+        return dict(*args, **kwargs)
+
+    _dict_new.__text_signature__ = '($cls, _typename, _fields=None, /, **kwargs)'
+
+    def _typeddict_new(*args, total=True, **kwargs):
+        if not args:
+            raise TypeError('TypedDict.__new__(): not enough arguments')
+        _, args = args[0], args[1:]  # allow the "cls" keyword be passed
+        if args:
+            typename, args = args[0], args[1:]  # allow the "_typename" keyword be passed
+        elif '_typename' in kwargs:
+            typename = kwargs.pop('_typename')
+            import warnings
+            warnings.warn("Passing '_typename' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        else:
+            raise TypeError("TypedDict.__new__() missing 1 required positional "
+                            "argument: '_typename'")
+        if args:
+            try:
+                fields, = args  # allow the "_fields" keyword be passed
+            except ValueError:
+                raise TypeError('TypedDict.__new__() takes from 2 to 3 '
+                                'positional arguments but {} '
+                                'were given'.format(len(args) + 2))
+        elif '_fields' in kwargs and len(kwargs) == 1:
+            fields = kwargs.pop('_fields')
+            import warnings
+            warnings.warn("Passing '_fields' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        else:
+            fields = None
+
+        if fields is None:
+            fields = kwargs
+        elif kwargs:
+            raise TypeError("TypedDict takes either a dict or keyword arguments,"
+                            " but not both")
+
+        ns = {'__annotations__': dict(fields), '__total__': total}
+        try:
+            # Setting correct module is necessary to make typed dict classes pickleable.
+            ns['__module__'] = sys._getframe(1).f_globals.get('__name__', '__main__')
+        except (AttributeError, ValueError):
+            pass
+
+        return _TypedDictMeta(typename, (), ns)
+
+    _typeddict_new.__text_signature__ = ('($cls, _typename, _fields=None,'
+                                         ' /, *, total=True, **kwargs)')
+
+    class _TypedDictMeta(type):
+        def __new__(cls, name, bases, ns, total=True):
+            # Create new typed dict class object.
+            # This method is called directly when TypedDict is subclassed,
+            # or via _typeddict_new when TypedDict is instantiated. This way
+            # TypedDict supports all three syntaxes described in its docstring.
+            # Subclasses and instances of TypedDict return actual dictionaries
+            # via _dict_new.
+            ns['__new__'] = _typeddict_new if name == 'TypedDict' else _dict_new
+            tp_dict = super(_TypedDictMeta, cls).__new__(cls, name, (dict,), ns)
+
+            annotations = {}
+            own_annotations = ns.get('__annotations__', {})
+            own_annotation_keys = set(own_annotations.keys())
+            msg = "TypedDict('Name', {f0: t0, f1: t1, ...}); each t must be a type"
+            own_annotations = {
+                n: typing._type_check(tp, msg) for n, tp in own_annotations.items()
+            }
+            required_keys = set()
+            optional_keys = set()
+
+            for base in bases:
+                annotations.update(base.__dict__.get('__annotations__', {}))
+                required_keys.update(base.__dict__.get('__required_keys__', ()))
+                optional_keys.update(base.__dict__.get('__optional_keys__', ()))
+
+            annotations.update(own_annotations)
+            if total:
+                required_keys.update(own_annotation_keys)
+            else:
+                optional_keys.update(own_annotation_keys)
+
+            tp_dict.__annotations__ = annotations
+            tp_dict.__required_keys__ = frozenset(required_keys)
+            tp_dict.__optional_keys__ = frozenset(optional_keys)
+            if not hasattr(tp_dict, '__total__'):
+                tp_dict.__total__ = total
+            return tp_dict
+
+        __instancecheck__ = __subclasscheck__ = _check_fails
+
+    TypedDict = _TypedDictMeta('TypedDict', (dict,), {})
+    TypedDict.__module__ = __name__
+    TypedDict.__doc__ = \
+        """A simple typed name space. At runtime it is equivalent to a plain dict.
+
+        TypedDict creates a dictionary type that expects all of its
+        instances to have a certain set of keys, with each key
+        associated with a value of a consistent type. This expectation
+        is not checked at runtime but is only enforced by type checkers.
+        Usage::
+
+            class Point2D(TypedDict):
+                x: int
+                y: int
+                label: str
+
+            a: Point2D = {'x': 1, 'y': 2, 'label': 'good'}  # OK
+            b: Point2D = {'z': 3, 'label': 'bad'}           # Fails type check
+
+            assert Point2D(x=1, y=2, label='first') == dict(x=1, y=2, label='first')
+
+        The type info can be accessed via the Point2D.__annotations__ dict, and
+        the Point2D.__required_keys__ and Point2D.__optional_keys__ frozensets.
+        TypedDict supports two additional equivalent forms::
+
+            Point2D = TypedDict('Point2D', x=int, y=int, label=str)
+            Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str})
+
+        The class syntax is only supported in Python 3.6+, while two other
+        syntax forms work for Python 2.7 and 3.2+
+        """
+
+
+# Python 3.9+ has PEP 593 (Annotated and modified get_type_hints)
+if hasattr(typing, 'Annotated'):
+    Annotated = typing.Annotated
+    get_type_hints = typing.get_type_hints
+    # Not exported and not a public API, but needed for get_origin() and get_args()
+    # to work.
+    _AnnotatedAlias = typing._AnnotatedAlias
+elif PEP_560:
+    class _AnnotatedAlias(typing._GenericAlias, _root=True):
+        """Runtime representation of an annotated type.
+
+        At its core 'Annotated[t, dec1, dec2, ...]' is an alias for the type 't'
+        with extra annotations. The alias behaves like a normal typing alias,
+        instantiating is the same as instantiating the underlying type, binding
+        it to types is also the same.
+        """
+        def __init__(self, origin, metadata):
+            if isinstance(origin, _AnnotatedAlias):
+                metadata = origin.__metadata__ + metadata
+                origin = origin.__origin__
+            super().__init__(origin, origin)
+            self.__metadata__ = metadata
+
+        def copy_with(self, params):
+            assert len(params) == 1
+            new_type = params[0]
+            return _AnnotatedAlias(new_type, self.__metadata__)
+
+        def __repr__(self):
+            return "typing_extensions.Annotated[{}, {}]".format(
+                typing._type_repr(self.__origin__),
+                ", ".join(repr(a) for a in self.__metadata__)
+            )
+
+        def __reduce__(self):
+            return operator.getitem, (
+                Annotated, (self.__origin__,) + self.__metadata__
+            )
+
+        def __eq__(self, other):
+            if not isinstance(other, _AnnotatedAlias):
+                return NotImplemented
+            if self.__origin__ != other.__origin__:
+                return False
+            return self.__metadata__ == other.__metadata__
+
+        def __hash__(self):
+            return hash((self.__origin__, self.__metadata__))
+
+    class Annotated:
+        """Add context specific metadata to a type.
+
+        Example: Annotated[int, runtime_check.Unsigned] indicates to the
+        hypothetical runtime_check module that this type is an unsigned int.
+        Every other consumer of this type can ignore this metadata and treat
+        this type as int.
+
+        The first argument to Annotated must be a valid type (and will be in
+        the __origin__ field), the remaining arguments are kept as a tuple in
+        the __extra__ field.
+
+        Details:
+
+        - It's an error to call `Annotated` with less than two arguments.
+        - Nested Annotated are flattened::
+
+            Annotated[Annotated[T, Ann1, Ann2], Ann3] == Annotated[T, Ann1, Ann2, Ann3]
+
+        - Instantiating an annotated type is equivalent to instantiating the
+        underlying type::
+
+            Annotated[C, Ann1](5) == C(5)
+
+        - Annotated can be used as a generic type alias::
+
+            Optimized = Annotated[T, runtime.Optimize()]
+            Optimized[int] == Annotated[int, runtime.Optimize()]
+
+            OptimizedList = Annotated[List[T], runtime.Optimize()]
+            OptimizedList[int] == Annotated[List[int], runtime.Optimize()]
+        """
+
+        __slots__ = ()
+
+        def __new__(cls, *args, **kwargs):
+            raise TypeError("Type Annotated cannot be instantiated.")
+
+        @_tp_cache
+        def __class_getitem__(cls, params):
+            if not isinstance(params, tuple) or len(params) < 2:
+                raise TypeError("Annotated[...] should be used "
+                                "with at least two arguments (a type and an "
+                                "annotation).")
+            msg = "Annotated[t, ...]: t must be a type."
+            origin = typing._type_check(params[0], msg)
+            metadata = tuple(params[1:])
+            return _AnnotatedAlias(origin, metadata)
+
+        def __init_subclass__(cls, *args, **kwargs):
+            raise TypeError(
+                "Cannot subclass {}.Annotated".format(cls.__module__)
+            )
+
+    def _strip_annotations(t):
+        """Strips the annotations from a given type.
+        """
+        if isinstance(t, _AnnotatedAlias):
+            return _strip_annotations(t.__origin__)
+        if isinstance(t, typing._GenericAlias):
+            stripped_args = tuple(_strip_annotations(a) for a in t.__args__)
+            if stripped_args == t.__args__:
+                return t
+            res = t.copy_with(stripped_args)
+            res._special = t._special
+            return res
+        return t
+
+    def get_type_hints(obj, globalns=None, localns=None, include_extras=False):
+        """Return type hints for an object.
+
+        This is often the same as obj.__annotations__, but it handles
+        forward references encoded as string literals, adds Optional[t] if a
+        default value equal to None is set and recursively replaces all
+        'Annotated[T, ...]' with 'T' (unless 'include_extras=True').
+
+        The argument may be a module, class, method, or function. The annotations
+        are returned as a dictionary. For classes, annotations include also
+        inherited members.
+
+        TypeError is raised if the argument is not of a type that can contain
+        annotations, and an empty dictionary is returned if no annotations are
+        present.
+
+        BEWARE -- the behavior of globalns and localns is counterintuitive
+        (unless you are familiar with how eval() and exec() work).  The
+        search order is locals first, then globals.
+
+        - If no dict arguments are passed, an attempt is made to use the
+          globals from obj (or the respective module's globals for classes),
+          and these are also used as the locals.  If the object does not appear
+          to have globals, an empty dictionary is used.
+
+        - If one dict argument is passed, it is used for both globals and
+          locals.
+
+        - If two dict arguments are passed, they specify globals and
+          locals, respectively.
+        """
+        hint = typing.get_type_hints(obj, globalns=globalns, localns=localns)
+        if include_extras:
+            return hint
+        return {k: _strip_annotations(t) for k, t in hint.items()}
+
+elif HAVE_ANNOTATED:
+
+    def _is_dunder(name):
+        """Returns True if name is a __dunder_variable_name__."""
+        return len(name) > 4 and name.startswith('__') and name.endswith('__')
+
+    # Prior to Python 3.7 types did not have `copy_with`. A lot of the equality
+    # checks, argument expansion etc. are done on the _subs_tre. As a result we
+    # can't provide a get_type_hints function that strips out annotations.
+
+    class AnnotatedMeta(typing.GenericMeta):
+        """Metaclass for Annotated"""
+
+        def __new__(cls, name, bases, namespace, **kwargs):
+            if any(b is not object for b in bases):
+                raise TypeError("Cannot subclass " + str(Annotated))
+            return super().__new__(cls, name, bases, namespace, **kwargs)
+
+        @property
+        def __metadata__(self):
+            return self._subs_tree()[2]
+
+        def _tree_repr(self, tree):
+            cls, origin, metadata = tree
+            if not isinstance(origin, tuple):
+                tp_repr = typing._type_repr(origin)
+            else:
+                tp_repr = origin[0]._tree_repr(origin)
+            metadata_reprs = ", ".join(repr(arg) for arg in metadata)
+            return '%s[%s, %s]' % (cls, tp_repr, metadata_reprs)
+
+        def _subs_tree(self, tvars=None, args=None):  # noqa
+            if self is Annotated:
+                return Annotated
+            res = super()._subs_tree(tvars=tvars, args=args)
+            # Flatten nested Annotated
+            if isinstance(res[1], tuple) and res[1][0] is Annotated:
+                sub_tp = res[1][1]
+                sub_annot = res[1][2]
+                return (Annotated, sub_tp, sub_annot + res[2])
+            return res
+
+        def _get_cons(self):
+            """Return the class used to create instance of this type."""
+            if self.__origin__ is None:
+                raise TypeError("Cannot get the underlying type of a "
+                                "non-specialized Annotated type.")
+            tree = self._subs_tree()
+            while isinstance(tree, tuple) and tree[0] is Annotated:
+                tree = tree[1]
+            if isinstance(tree, tuple):
+                return tree[0]
+            else:
+                return tree
+
+        @_tp_cache
+        def __getitem__(self, params):
+            if not isinstance(params, tuple):
+                params = (params,)
+            if self.__origin__ is not None:  # specializing an instantiated type
+                return super().__getitem__(params)
+            elif not isinstance(params, tuple) or len(params) < 2:
+                raise TypeError("Annotated[...] should be instantiated "
+                                "with at least two arguments (a type and an "
+                                "annotation).")
+            else:
+                msg = "Annotated[t, ...]: t must be a type."
+                tp = typing._type_check(params[0], msg)
+                metadata = tuple(params[1:])
+            return self.__class__(
+                self.__name__,
+                self.__bases__,
+                _no_slots_copy(self.__dict__),
+                tvars=_type_vars((tp,)),
+                # Metadata is a tuple so it won't be touched by _replace_args et al.
+                args=(tp, metadata),
+                origin=self,
+            )
+
+        def __call__(self, *args, **kwargs):
+            cons = self._get_cons()
+            result = cons(*args, **kwargs)
+            try:
+                result.__orig_class__ = self
+            except AttributeError:
+                pass
+            return result
+
+        def __getattr__(self, attr):
+            # For simplicity we just don't relay all dunder names
+            if self.__origin__ is not None and not _is_dunder(attr):
+                return getattr(self._get_cons(), attr)
+            raise AttributeError(attr)
+
+        def __setattr__(self, attr, value):
+            if _is_dunder(attr) or attr.startswith('_abc_'):
+                super().__setattr__(attr, value)
+            elif self.__origin__ is None:
+                raise AttributeError(attr)
+            else:
+                setattr(self._get_cons(), attr, value)
+
+        def __instancecheck__(self, obj):
+            raise TypeError("Annotated cannot be used with isinstance().")
+
+        def __subclasscheck__(self, cls):
+            raise TypeError("Annotated cannot be used with issubclass().")
+
+    class Annotated(metaclass=AnnotatedMeta):
+        """Add context specific metadata to a type.
+
+        Example: Annotated[int, runtime_check.Unsigned] indicates to the
+        hypothetical runtime_check module that this type is an unsigned int.
+        Every other consumer of this type can ignore this metadata and treat
+        this type as int.
+
+        The first argument to Annotated must be a valid type, the remaining
+        arguments are kept as a tuple in the __metadata__ field.
+
+        Details:
+
+        - It's an error to call `Annotated` with less than two arguments.
+        - Nested Annotated are flattened::
+
+            Annotated[Annotated[T, Ann1, Ann2], Ann3] == Annotated[T, Ann1, Ann2, Ann3]
+
+        - Instantiating an annotated type is equivalent to instantiating the
+        underlying type::
+
+            Annotated[C, Ann1](5) == C(5)
+
+        - Annotated can be used as a generic type alias::
+
+            Optimized = Annotated[T, runtime.Optimize()]
+            Optimized[int] == Annotated[int, runtime.Optimize()]
+
+            OptimizedList = Annotated[List[T], runtime.Optimize()]
+            OptimizedList[int] == Annotated[List[int], runtime.Optimize()]
+        """
+
+# Python 3.8 has get_origin() and get_args() but those implementations aren't
+# Annotated-aware, so we can't use those, only Python 3.9 versions will do.
+if sys.version_info[:2] >= (3, 9):
+    get_origin = typing.get_origin
+    get_args = typing.get_args
+elif PEP_560:
+    from typing import _GenericAlias  # noqa
+
+    def get_origin(tp):
+        """Get the unsubscripted version of a type.
+
+        This supports generic types, Callable, Tuple, Union, Literal, Final, ClassVar
+        and Annotated. Return None for unsupported types. Examples::
+
+            get_origin(Literal[42]) is Literal
+            get_origin(int) is None
+            get_origin(ClassVar[int]) is ClassVar
+            get_origin(Generic) is Generic
+            get_origin(Generic[T]) is Generic
+            get_origin(Union[T, int]) is Union
+            get_origin(List[Tuple[T, T]][int]) == list
+        """
+        if isinstance(tp, _AnnotatedAlias):
+            return Annotated
+        if isinstance(tp, _GenericAlias):
+            return tp.__origin__
+        if tp is Generic:
+            return Generic
+        return None
+
+    def get_args(tp):
+        """Get type arguments with all substitutions performed.
+
+        For unions, basic simplifications used by Union constructor are performed.
+        Examples::
+            get_args(Dict[str, int]) == (str, int)
+            get_args(int) == ()
+            get_args(Union[int, Union[T, int], str][int]) == (int, str)
+            get_args(Union[int, Tuple[T, int]][str]) == (int, Tuple[str, int])
+            get_args(Callable[[], T][int]) == ([], int)
+        """
+        if isinstance(tp, _AnnotatedAlias):
+            return (tp.__origin__,) + tp.__metadata__
+        if isinstance(tp, _GenericAlias):
+            res = tp.__args__
+            if get_origin(tp) is collections.abc.Callable and res[0] is not Ellipsis:
+                res = (list(res[:-1]), res[-1])
+            return res
+        return ()