oss ydb: fix dstool building and test run

1 files changed, 2550 insertions, 0 deletions

diff --git a/contrib/deprecated/python/typing/typing.py b/contrib/deprecated/python/typing/typing.py
new file mode 100644
index 0000000000..dd16d9af96
--- /dev/null
+++ b/contrib/deprecated/python/typing/typing.py
@@ -0,0 +1,2550 @@
+from __future__ import absolute_import, unicode_literals
+
+import abc
+from abc import abstractmethod, abstractproperty
+import collections
+import functools
+import re as stdlib_re  # Avoid confusion with the re we export.
+import sys
+import types
+import copy
+try:
+    import collections.abc as collections_abc
+except ImportError:
+    import collections as collections_abc  # Fallback for PY3.2.
+
+
+# Please keep __all__ alphabetized within each category.
+__all__ = [
+    # Super-special typing primitives.
+    'Any',
+    'Callable',
+    'ClassVar',
+    'Final',
+    'Generic',
+    'Literal',
+    'Optional',
+    'Protocol',
+    'Tuple',
+    'Type',
+    'TypeVar',
+    'Union',
+
+    # ABCs (from collections.abc).
+    'AbstractSet',  # collections.abc.Set.
+    'GenericMeta',  # subclass of abc.ABCMeta and a metaclass
+                    # for 'Generic' and ABCs below.
+    'ByteString',
+    'Container',
+    'ContextManager',
+    'Hashable',
+    'ItemsView',
+    'Iterable',
+    'Iterator',
+    'KeysView',
+    'Mapping',
+    'MappingView',
+    'MutableMapping',
+    'MutableSequence',
+    'MutableSet',
+    'Sequence',
+    'Sized',
+    'ValuesView',
+
+    # Structural checks, a.k.a. protocols.
+    'Reversible',
+    'SupportsAbs',
+    'SupportsComplex',
+    'SupportsFloat',
+    'SupportsIndex',
+    'SupportsInt',
+
+    # Concrete collection types.
+    'Counter',
+    'Deque',
+    'Dict',
+    'DefaultDict',
+    'List',
+    'Set',
+    'FrozenSet',
+    'NamedTuple',  # Not really a type.
+    'TypedDict',  # Not really a type.
+    'Generator',
+
+    # One-off things.
+    'AnyStr',
+    'cast',
+    'final',
+    'get_type_hints',
+    'NewType',
+    'no_type_check',
+    'no_type_check_decorator',
+    'NoReturn',
+    'overload',
+    'runtime_checkable',
+    'Text',
+    'TYPE_CHECKING',
+]
+
+# The pseudo-submodules 're' and 'io' are part of the public
+# namespace, but excluded from __all__ because they might stomp on
+# legitimate imports of those modules.
+
+
+def _qualname(x):
+    if sys.version_info[:2] >= (3, 3):
+        return x.__qualname__
+    else:
+        # Fall back to just name.
+        return x.__name__
+
+
+def _trim_name(nm):
+    whitelist = ('_TypeAlias', '_ForwardRef', '_TypingBase', '_FinalTypingBase')
+    if nm.startswith('_') and nm not in whitelist:
+        nm = nm[1:]
+    return nm
+
+
+class TypingMeta(type):
+    """Metaclass for most types defined in typing module
+    (not a part of public API).
+
+    This also defines a dummy constructor (all the work for most typing
+    constructs is done in __new__) and a nicer repr().
+    """
+
+    _is_protocol = False
+
+    def __new__(cls, name, bases, namespace):
+        return super(TypingMeta, cls).__new__(cls, str(name), bases, namespace)
+
+    @classmethod
+    def assert_no_subclassing(cls, bases):
+        for base in bases:
+            if isinstance(base, cls):
+                raise TypeError("Cannot subclass %s" %
+                                (', '.join(map(_type_repr, bases)) or '()'))
+
+    def __init__(self, *args, **kwds):
+        pass
+
+    def _eval_type(self, globalns, localns):
+        """Override this in subclasses to interpret forward references.
+
+        For example, List['C'] is internally stored as
+        List[_ForwardRef('C')], which should evaluate to List[C],
+        where C is an object found in globalns or localns (searching
+        localns first, of course).
+        """
+        return self
+
+    def _get_type_vars(self, tvars):
+        pass
+
+    def __repr__(self):
+        qname = _trim_name(_qualname(self))
+        return '%s.%s' % (self.__module__, qname)
+
+
+class _TypingBase(object):
+    """Internal indicator of special typing constructs."""
+    __metaclass__ = TypingMeta
+    __slots__ = ('__weakref__',)
+
+    def __init__(self, *args, **kwds):
+        pass
+
+    def __new__(cls, *args, **kwds):
+        """Constructor.
+
+        This only exists to give a better error message in case
+        someone tries to subclass a special typing object (not a good idea).
+        """
+        if (len(args) == 3 and
+                isinstance(args[0], str) and
+                isinstance(args[1], tuple)):
+            # Close enough.
+            raise TypeError("Cannot subclass %r" % cls)
+        return super(_TypingBase, cls).__new__(cls)
+
+    # Things that are not classes also need these.
+    def _eval_type(self, globalns, localns):
+        return self
+
+    def _get_type_vars(self, tvars):
+        pass
+
+    def __repr__(self):
+        cls = type(self)
+        qname = _trim_name(_qualname(cls))
+        return '%s.%s' % (cls.__module__, qname)
+
+    def __call__(self, *args, **kwds):
+        raise TypeError("Cannot instantiate %r" % type(self))
+
+
+class _FinalTypingBase(_TypingBase):
+    """Internal mix-in class to prevent instantiation.
+
+    Prevents instantiation unless _root=True is given in class call.
+    It is used to create pseudo-singleton instances Any, Union, Optional, etc.
+    """
+
+    __slots__ = ()
+
+    def __new__(cls, *args, **kwds):
+        self = super(_FinalTypingBase, cls).__new__(cls, *args, **kwds)
+        if '_root' in kwds and kwds['_root'] is True:
+            return self
+        raise TypeError("Cannot instantiate %r" % cls)
+
+    def __reduce__(self):
+        return _trim_name(type(self).__name__)
+
+
+class _ForwardRef(_TypingBase):
+    """Internal wrapper to hold a forward reference."""
+
+    __slots__ = ('__forward_arg__', '__forward_code__',
+                 '__forward_evaluated__', '__forward_value__')
+
+    def __init__(self, arg):
+        super(_ForwardRef, self).__init__(arg)
+        if not isinstance(arg, basestring):
+            raise TypeError('Forward reference must be a string -- got %r' % (arg,))
+        try:
+            code = compile(arg, '<string>', 'eval')
+        except SyntaxError:
+            raise SyntaxError('Forward reference must be an expression -- got %r' %
+                              (arg,))
+        self.__forward_arg__ = arg
+        self.__forward_code__ = code
+        self.__forward_evaluated__ = False
+        self.__forward_value__ = None
+
+    def _eval_type(self, globalns, localns):
+        if not self.__forward_evaluated__ or localns is not globalns:
+            if globalns is None and localns is None:
+                globalns = localns = {}
+            elif globalns is None:
+                globalns = localns
+            elif localns is None:
+                localns = globalns
+            self.__forward_value__ = _type_check(
+                eval(self.__forward_code__, globalns, localns),
+                "Forward references must evaluate to types.")
+            self.__forward_evaluated__ = True
+        return self.__forward_value__
+
+    def __eq__(self, other):
+        if not isinstance(other, _ForwardRef):
+            return NotImplemented
+        return (self.__forward_arg__ == other.__forward_arg__ and
+                self.__forward_value__ == other.__forward_value__)
+
+    def __hash__(self):
+        return hash((self.__forward_arg__, self.__forward_value__))
+
+    def __instancecheck__(self, obj):
+        raise TypeError("Forward references cannot be used with isinstance().")
+
+    def __subclasscheck__(self, cls):
+        raise TypeError("Forward references cannot be used with issubclass().")
+
+    def __repr__(self):
+        return '_ForwardRef(%r)' % (self.__forward_arg__,)
+
+
+class _TypeAlias(_TypingBase):
+    """Internal helper class for defining generic variants of concrete types.
+
+    Note that this is not a type; let's call it a pseudo-type.  It cannot
+    be used in instance and subclass checks in parameterized form, i.e.
+    ``isinstance(42, Match[str])`` raises ``TypeError`` instead of returning
+    ``False``.
+    """
+
+    __slots__ = ('name', 'type_var', 'impl_type', 'type_checker')
+
+    def __init__(self, name, type_var, impl_type, type_checker):
+        """Initializer.
+
+        Args:
+            name: The name, e.g. 'Pattern'.
+            type_var: The type parameter, e.g. AnyStr, or the
+                specific type, e.g. str.
+            impl_type: The implementation type.
+            type_checker: Function that takes an impl_type instance.
+                and returns a value that should be a type_var instance.
+        """
+        assert isinstance(name, basestring), repr(name)
+        assert isinstance(impl_type, type), repr(impl_type)
+        assert not isinstance(impl_type, TypingMeta), repr(impl_type)
+        assert isinstance(type_var, (type, _TypingBase)), repr(type_var)
+        self.name = name
+        self.type_var = type_var
+        self.impl_type = impl_type
+        self.type_checker = type_checker
+
+    def __repr__(self):
+        return "%s[%s]" % (self.name, _type_repr(self.type_var))
+
+    def __getitem__(self, parameter):
+        if not isinstance(self.type_var, TypeVar):
+            raise TypeError("%s cannot be further parameterized." % self)
+        if self.type_var.__constraints__ and isinstance(parameter, type):
+            if not issubclass(parameter, self.type_var.__constraints__):
+                raise TypeError("%s is not a valid substitution for %s." %
+                                (parameter, self.type_var))
+        if isinstance(parameter, TypeVar) and parameter is not self.type_var:
+            raise TypeError("%s cannot be re-parameterized." % self)
+        return self.__class__(self.name, parameter,
+                              self.impl_type, self.type_checker)
+
+    def __eq__(self, other):
+        if not isinstance(other, _TypeAlias):
+            return NotImplemented
+        return self.name == other.name and self.type_var == other.type_var
+
+    def __hash__(self):
+        return hash((self.name, self.type_var))
+
+    def __instancecheck__(self, obj):
+        if not isinstance(self.type_var, TypeVar):
+            raise TypeError("Parameterized type aliases cannot be used "
+                            "with isinstance().")
+        return isinstance(obj, self.impl_type)
+
+    def __subclasscheck__(self, cls):
+        if not isinstance(self.type_var, TypeVar):
+            raise TypeError("Parameterized type aliases cannot be used "
+                            "with issubclass().")
+        return issubclass(cls, self.impl_type)
+
+
+def _get_type_vars(types, tvars):
+    for t in types:
+        if isinstance(t, TypingMeta) or isinstance(t, _TypingBase):
+            t._get_type_vars(tvars)
+
+
+def _type_vars(types):
+    tvars = []
+    _get_type_vars(types, tvars)
+    return tuple(tvars)
+
+
+def _eval_type(t, globalns, localns):
+    if isinstance(t, TypingMeta) or isinstance(t, _TypingBase):
+        return t._eval_type(globalns, localns)
+    return t
+
+
+def _type_check(arg, msg):
+    """Check that the argument is a type, and return it (internal helper).
+
+    As a special case, accept None and return type(None) instead.
+    Also, _TypeAlias instances (e.g. Match, Pattern) are acceptable.
+
+    The msg argument is a human-readable error message, e.g.
+
+        "Union[arg, ...]: arg should be a type."
+
+    We append the repr() of the actual value (truncated to 100 chars).
+    """
+    if arg is None:
+        return type(None)
+    if isinstance(arg, basestring):
+        arg = _ForwardRef(arg)
+    if (
+        isinstance(arg, _TypingBase) and type(arg).__name__ == '_ClassVar' or
+        not isinstance(arg, (type, _TypingBase)) and not callable(arg)
+    ):
+        raise TypeError(msg + " Got %.100r." % (arg,))
+    # Bare Union etc. are not valid as type arguments
+    if (
+        type(arg).__name__ in ('_Union', '_Optional') and
+        not getattr(arg, '__origin__', None) or
+        isinstance(arg, TypingMeta) and arg._gorg in (Generic, Protocol)
+    ):
+        raise TypeError("Plain %s is not valid as type argument" % arg)
+    return arg
+
+
+def _type_repr(obj):
+    """Return the repr() of an object, special-casing types (internal helper).
+
+    If obj is a type, we return a shorter version than the default
+    type.__repr__, based on the module and qualified name, which is
+    typically enough to uniquely identify a type.  For everything
+    else, we fall back on repr(obj).
+    """
+    if isinstance(obj, type) and not isinstance(obj, TypingMeta):
+        if obj.__module__ == '__builtin__':
+            return _qualname(obj)
+        return '%s.%s' % (obj.__module__, _qualname(obj))
+    if obj is Ellipsis:
+        return '...'
+    if isinstance(obj, types.FunctionType):
+        return obj.__name__
+    return repr(obj)
+
+
+class ClassVarMeta(TypingMeta):
+    """Metaclass for _ClassVar"""
+
+    def __new__(cls, name, bases, namespace):
+        cls.assert_no_subclassing(bases)
+        self = super(ClassVarMeta, cls).__new__(cls, name, bases, namespace)
+        return self
+
+
+class _ClassVar(_FinalTypingBase):
+    """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 = {}  # type: ClassVar[Dict[str, int]] # class variable
+          damage = 10 # type: int                      # 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().
+    """
+
+    __metaclass__ = ClassVarMeta
+    __slots__ = ('__type__',)
+
+    def __init__(self, tp=None, _root=False):
+        self.__type__ = tp
+
+    def __getitem__(self, item):
+        cls = type(self)
+        if self.__type__ is None:
+            return cls(_type_check(item,
+                       '{} accepts only types.'.format(cls.__name__[1:])),
+                       _root=True)
+        raise TypeError('{} cannot be further subscripted'
+                        .format(cls.__name__[1:]))
+
+    def _eval_type(self, globalns, localns):
+        return type(self)(_eval_type(self.__type__, globalns, localns),
+                          _root=True)
+
+    def __repr__(self):
+        r = super(_ClassVar, self).__repr__()
+        if self.__type__ is not None:
+            r += '[{}]'.format(_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)
+
+
+class _FinalMeta(TypingMeta):
+    """Metaclass for _Final"""
+
+    def __new__(cls, name, bases, namespace):
+        cls.assert_no_subclassing(bases)
+        self = super(_FinalMeta, cls).__new__(cls, name, bases, namespace)
+        return self
+
+
+class _Final(_FinalTypingBase):
+    """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.
+    """
+
+    __metaclass__ = _FinalMeta
+    __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(_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 = _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(_Final, self).__repr__()
+        if self.__type__ is not None:
+            r += '[{}]'.format(_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)
+
+
+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
+
+
+class _LiteralMeta(TypingMeta):
+    """Metaclass for _Literal"""
+
+    def __new__(cls, name, bases, namespace):
+        cls.assert_no_subclassing(bases)
+        self = super(_LiteralMeta, cls).__new__(cls, name, bases, namespace)
+        return self
+
+
+class _Literal(_FinalTypingBase):
+    """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.
+    """
+
+    __metaclass__ = _LiteralMeta
+    __slots__ = ('__values__',)
+
+    def __init__(self, values=None, **kwds):
+        self.__values__ = values
+
+    def __getitem__(self, item):
+        cls = type(self)
+        if self.__values__ is None:
+            if not isinstance(item, tuple):
+                item = (item,)
+            return cls(values=item,
+                       _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(_Literal, self).__repr__()
+        if self.__values__ is not None:
+            r += '[{}]'.format(', '.join(map(_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)
+
+
+class AnyMeta(TypingMeta):
+    """Metaclass for Any."""
+
+    def __new__(cls, name, bases, namespace):
+        cls.assert_no_subclassing(bases)
+        self = super(AnyMeta, cls).__new__(cls, name, bases, namespace)
+        return self
+
+
+class _Any(_FinalTypingBase):
+    """Special type indicating an unconstrained type.
+
+    - Any is compatible with every type.
+    - Any assumed to have all methods.
+    - All values assumed to be instances of Any.
+
+    Note that all the above statements are true from the point of view of
+    static type checkers. At runtime, Any should not be used with instance
+    or class checks.
+    """
+    __metaclass__ = AnyMeta
+    __slots__ = ()
+
+    def __instancecheck__(self, obj):
+        raise TypeError("Any cannot be used with isinstance().")
+
+    def __subclasscheck__(self, cls):
+        raise TypeError("Any cannot be used with issubclass().")
+
+
+Any = _Any(_root=True)
+
+
+class NoReturnMeta(TypingMeta):
+    """Metaclass for NoReturn."""
+
+    def __new__(cls, name, bases, namespace):
+        cls.assert_no_subclassing(bases)
+        self = super(NoReturnMeta, cls).__new__(cls, name, bases, namespace)
+        return self
+
+
+class _NoReturn(_FinalTypingBase):
+    """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.
+    """
+    __metaclass__ = NoReturnMeta
+    __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)
+
+
+class TypeVarMeta(TypingMeta):
+    def __new__(cls, name, bases, namespace):
+        cls.assert_no_subclassing(bases)
+        return super(TypeVarMeta, cls).__new__(cls, name, bases, namespace)
+
+
+class TypeVar(_TypingBase):
+    """Type variable.
+
+    Usage::
+
+      T = TypeVar('T')  # Can be anything
+      A = TypeVar('A', str, bytes)  # Must be str or bytes
+
+    Type variables exist primarily for the benefit of static type
+    checkers.  They serve as the parameters for generic types as well
+    as for generic function definitions.  See class Generic for more
+    information on generic types.  Generic functions work as follows:
+
+      def repeat(x: T, n: int) -> List[T]:
+          '''Return a list containing n references to x.'''
+          return [x]*n
+
+      def longest(x: A, y: A) -> A:
+          '''Return the longest of two strings.'''
+          return x if len(x) >= len(y) else y
+
+    The latter example's signature is essentially the overloading
+    of (str, str) -> str and (bytes, bytes) -> bytes.  Also note
+    that if the arguments are instances of some subclass of str,
+    the return type is still plain str.
+
+    At runtime, isinstance(x, T) and issubclass(C, T) will raise TypeError.
+
+    Type variables defined with covariant=True or contravariant=True
+    can be used do declare covariant or contravariant generic types.
+    See PEP 484 for more details. By default generic types are invariant
+    in all type variables.
+
+    Type variables can be introspected. e.g.:
+
+      T.__name__ == 'T'
+      T.__constraints__ == ()
+      T.__covariant__ == False
+      T.__contravariant__ = False
+      A.__constraints__ == (str, bytes)
+    """
+
+    __metaclass__ = TypeVarMeta
+    __slots__ = ('__name__', '__bound__', '__constraints__',
+                 '__covariant__', '__contravariant__')
+
+    def __init__(self, name, *constraints, **kwargs):
+        super(TypeVar, self).__init__(name, *constraints, **kwargs)
+        bound = kwargs.get('bound', None)
+        covariant = kwargs.get('covariant', False)
+        contravariant = kwargs.get('contravariant', False)
+        self.__name__ = name
+        if covariant and contravariant:
+            raise ValueError("Bivariant types are not supported.")
+        self.__covariant__ = bool(covariant)
+        self.__contravariant__ = bool(contravariant)
+        if constraints and bound is not None:
+            raise TypeError("Constraints cannot be combined with bound=...")
+        if constraints and len(constraints) == 1:
+            raise TypeError("A single constraint is not allowed")
+        msg = "TypeVar(name, constraint, ...): constraints must be types."
+        self.__constraints__ = tuple(_type_check(t, msg) for t in constraints)
+        if bound:
+            self.__bound__ = _type_check(bound, "Bound must be a type.")
+        else:
+            self.__bound__ = None
+
+    def _get_type_vars(self, tvars):
+        if self not in tvars:
+            tvars.append(self)
+
+    def __repr__(self):
+        if self.__covariant__:
+            prefix = '+'
+        elif self.__contravariant__:
+            prefix = '-'
+        else:
+            prefix = '~'
+        return prefix + self.__name__
+
+    def __instancecheck__(self, instance):
+        raise TypeError("Type variables cannot be used with isinstance().")
+
+    def __subclasscheck__(self, cls):
+        raise TypeError("Type variables cannot be used with issubclass().")
+
+
+# Some unconstrained type variables.  These are used by the container types.
+# (These are not for export.)
+T = TypeVar('T')  # Any type.
+KT = TypeVar('KT')  # Key type.
+VT = TypeVar('VT')  # Value type.
+T_co = TypeVar('T_co', covariant=True)  # Any type covariant containers.
+V_co = TypeVar('V_co', covariant=True)  # Any type covariant containers.
+VT_co = TypeVar('VT_co', covariant=True)  # Value type covariant containers.
+T_contra = TypeVar('T_contra', contravariant=True)  # Ditto contravariant.
+
+# A useful type variable with constraints.  This represents string types.
+# (This one *is* for export!)
+AnyStr = TypeVar('AnyStr', bytes, unicode)
+
+
+def _replace_arg(arg, tvars, args):
+    """An internal helper function: replace arg if it is a type variable
+    found in tvars with corresponding substitution from args or
+    with corresponding substitution sub-tree if arg is a generic type.
+    """
+
+    if tvars is None:
+        tvars = []
+    if hasattr(arg, '_subs_tree') and isinstance(arg, (GenericMeta, _TypingBase)):
+        return arg._subs_tree(tvars, args)
+    if isinstance(arg, TypeVar):
+        for i, tvar in enumerate(tvars):
+            if arg == tvar:
+                return args[i]
+    return arg
+
+
+# Special typing constructs Union, Optional, Generic, Callable and Tuple
+# use three special attributes for internal bookkeeping of generic types:
+# * __parameters__ is a tuple of unique free type parameters of a generic
+#   type, for example, Dict[T, T].__parameters__ == (T,);
+# * __origin__ keeps a reference to a type that was subscripted,
+#   e.g., Union[T, int].__origin__ == Union;
+# * __args__ is a tuple of all arguments used in subscripting,
+#   e.g., Dict[T, int].__args__ == (T, int).
+
+
+def _subs_tree(cls, tvars=None, args=None):
+    """An internal helper function: calculate substitution tree
+    for generic cls after replacing its type parameters with
+    substitutions in tvars -> args (if any).
+    Repeat the same following __origin__'s.
+
+    Return a list of arguments with all possible substitutions
+    performed. Arguments that are generic classes themselves are represented
+    as tuples (so that no new classes are created by this function).
+    For example: _subs_tree(List[Tuple[int, T]][str]) == [(Tuple, int, str)]
+    """
+
+    if cls.__origin__ is None:
+        return cls
+    # Make of chain of origins (i.e. cls -> cls.__origin__)
+    current = cls.__origin__
+    orig_chain = []
+    while current.__origin__ is not None:
+        orig_chain.append(current)
+        current = current.__origin__
+    # Replace type variables in __args__ if asked ...
+    tree_args = []
+    for arg in cls.__args__:
+        tree_args.append(_replace_arg(arg, tvars, args))
+    # ... then continue replacing down the origin chain.
+    for ocls in orig_chain:
+        new_tree_args = []
+        for arg in ocls.__args__:
+            new_tree_args.append(_replace_arg(arg, ocls.__parameters__, tree_args))
+        tree_args = new_tree_args
+    return tree_args
+
+
+def _remove_dups_flatten(parameters):
+    """An internal helper for Union creation and substitution: flatten Union's
+    among parameters, then remove duplicates and strict subclasses.
+    """
+
+    # Flatten out Union[Union[...], ...].
+    params = []
+    for p in parameters:
+        if isinstance(p, _Union) and p.__origin__ is Union:
+            params.extend(p.__args__)
+        elif isinstance(p, tuple) and len(p) > 0 and p[0] is Union:
+            params.extend(p[1:])
+        else:
+            params.append(p)
+    # Weed out strict duplicates, preserving the first of each occurrence.
+    all_params = set(params)
+    if len(all_params) < len(params):
+        new_params = []
+        for t in params:
+            if t in all_params:
+                new_params.append(t)
+                all_params.remove(t)
+        params = new_params
+        assert not all_params, all_params
+    # Weed out subclasses.
+    # E.g. Union[int, Employee, Manager] == Union[int, Employee].
+    # If object is present it will be sole survivor among proper classes.
+    # Never discard type variables.
+    # (In particular, Union[str, AnyStr] != AnyStr.)
+    all_params = set(params)
+    for t1 in params:
+        if not isinstance(t1, type):
+            continue
+        if any(isinstance(t2, type) and issubclass(t1, t2)
+               for t2 in all_params - {t1}
+               if not (isinstance(t2, GenericMeta) and
+                       t2.__origin__ is not None)):
+            all_params.remove(t1)
+    return tuple(t for t in params if t in all_params)
+
+
+def _check_generic(cls, parameters):
+    # Check correct count for parameters of a generic cls (internal helper).
+    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))
+
+
+_cleanups = []
+
+
+def _tp_cache(func):
+    maxsize = 128
+    cache = {}
+    _cleanups.append(cache.clear)
+
+    @functools.wraps(func)
+    def inner(*args):
+        key = args
+        try:
+            return cache[key]
+        except TypeError:
+            # Assume it's an unhashable argument.
+            return func(*args)
+        except KeyError:
+            value = func(*args)
+            if len(cache) >= maxsize:
+                # If the cache grows too much, just start over.
+                cache.clear()
+            cache[key] = value
+            return value
+
+    return inner
+
+
+class UnionMeta(TypingMeta):
+    """Metaclass for Union."""
+
+    def __new__(cls, name, bases, namespace):
+        cls.assert_no_subclassing(bases)
+        return super(UnionMeta, cls).__new__(cls, name, bases, namespace)
+
+
+class _Union(_FinalTypingBase):
+    """Union type; Union[X, Y] means either X or Y.
+
+    To define a union, use e.g. Union[int, str].  Details:
+
+    - The arguments must be types and there must be at least one.
+
+    - None as an argument is a special case and is replaced by
+      type(None).
+
+    - Unions of unions are flattened, e.g.::
+
+        Union[Union[int, str], float] == Union[int, str, float]
+
+    - Unions of a single argument vanish, e.g.::
+
+        Union[int] == int  # The constructor actually returns int
+
+    - Redundant arguments are skipped, e.g.::
+
+        Union[int, str, int] == Union[int, str]
+
+    - When comparing unions, the argument order is ignored, e.g.::
+
+        Union[int, str] == Union[str, int]
+
+    - When two arguments have a subclass relationship, the least
+      derived argument is kept, e.g.::
+
+        class Employee: pass
+        class Manager(Employee): pass
+        Union[int, Employee, Manager] == Union[int, Employee]
+        Union[Manager, int, Employee] == Union[int, Employee]
+        Union[Employee, Manager] == Employee
+
+    - Similar for object::
+
+        Union[int, object] == object
+
+    - You cannot subclass or instantiate a union.
+
+    - You can use Optional[X] as a shorthand for Union[X, None].
+    """
+
+    __metaclass__ = UnionMeta
+    __slots__ = ('__parameters__', '__args__', '__origin__', '__tree_hash__')
+
+    def __new__(cls, parameters=None, origin=None, *args, **kwds):
+        self = super(_Union, cls).__new__(cls, parameters, origin, *args, **kwds)
+        if origin is None:
+            self.__parameters__ = None
+            self.__args__ = None
+            self.__origin__ = None
+            self.__tree_hash__ = hash(frozenset(('Union',)))
+            return self
+        if not isinstance(parameters, tuple):
+            raise TypeError("Expected parameters=<tuple>")
+        if origin is Union:
+            parameters = _remove_dups_flatten(parameters)
+            # It's not a union if there's only one type left.
+            if len(parameters) == 1:
+                return parameters[0]
+        self.__parameters__ = _type_vars(parameters)
+        self.__args__ = parameters
+        self.__origin__ = origin
+        # Pre-calculate the __hash__ on instantiation.
+        # This improves speed for complex substitutions.
+        subs_tree = self._subs_tree()
+        if isinstance(subs_tree, tuple):
+            self.__tree_hash__ = hash(frozenset(subs_tree))
+        else:
+            self.__tree_hash__ = hash(subs_tree)
+        return self
+
+    def _eval_type(self, globalns, localns):
+        if self.__args__ is None:
+            return self
+        ev_args = tuple(_eval_type(t, globalns, localns) for t in self.__args__)
+        ev_origin = _eval_type(self.__origin__, globalns, localns)
+        if ev_args == self.__args__ and ev_origin == self.__origin__:
+            # Everything is already evaluated.
+            return self
+        return self.__class__(ev_args, ev_origin, _root=True)
+
+    def _get_type_vars(self, tvars):
+        if self.__origin__ and self.__parameters__:
+            _get_type_vars(self.__parameters__, tvars)
+
+    def __repr__(self):
+        if self.__origin__ is None:
+            return super(_Union, self).__repr__()
+        tree = self._subs_tree()
+        if not isinstance(tree, tuple):
+            return repr(tree)
+        return tree[0]._tree_repr(tree)
+
+    def _tree_repr(self, tree):
+        arg_list = []
+        for arg in tree[1:]:
+            if not isinstance(arg, tuple):
+                arg_list.append(_type_repr(arg))
+            else:
+                arg_list.append(arg[0]._tree_repr(arg))
+        return super(_Union, self).__repr__() + '[%s]' % ', '.join(arg_list)
+
+    @_tp_cache
+    def __getitem__(self, parameters):
+        if parameters == ():
+            raise TypeError("Cannot take a Union of no types.")
+        if not isinstance(parameters, tuple):
+            parameters = (parameters,)
+        if self.__origin__ is None:
+            msg = "Union[arg, ...]: each arg must be a type."
+        else:
+            msg = "Parameters to generic types must be types."
+        parameters = tuple(_type_check(p, msg) for p in parameters)
+        if self is not Union:
+            _check_generic(self, parameters)
+        return self.__class__(parameters, origin=self, _root=True)
+
+    def _subs_tree(self, tvars=None, args=None):
+        if self is Union:
+            return Union  # Nothing to substitute
+        tree_args = _subs_tree(self, tvars, args)
+        tree_args = _remove_dups_flatten(tree_args)
+        if len(tree_args) == 1:
+            return tree_args[0]  # Union of a single type is that type
+        return (Union,) + tree_args
+
+    def __eq__(self, other):
+        if isinstance(other, _Union):
+            return self.__tree_hash__ == other.__tree_hash__
+        elif self is not Union:
+            return self._subs_tree() == other
+        else:
+            return self is other
+
+    def __hash__(self):
+        return self.__tree_hash__
+
+    def __instancecheck__(self, obj):
+        raise TypeError("Unions cannot be used with isinstance().")
+
+    def __subclasscheck__(self, cls):
+        raise TypeError("Unions cannot be used with issubclass().")
+
+
+Union = _Union(_root=True)
+
+
+class OptionalMeta(TypingMeta):
+    """Metaclass for Optional."""
+
+    def __new__(cls, name, bases, namespace):
+        cls.assert_no_subclassing(bases)
+        return super(OptionalMeta, cls).__new__(cls, name, bases, namespace)
+
+
+class _Optional(_FinalTypingBase):
+    """Optional type.
+
+    Optional[X] is equivalent to Union[X, None].
+    """
+
+    __metaclass__ = OptionalMeta
+    __slots__ = ()
+
+    @_tp_cache
+    def __getitem__(self, arg):
+        arg = _type_check(arg, "Optional[t] requires a single type.")
+        return Union[arg, type(None)]
+
+
+Optional = _Optional(_root=True)
+
+
+def _next_in_mro(cls):
+    """Helper for Generic.__new__.
+
+    Returns the class after the last occurrence of Generic or
+    Generic[...] in cls.__mro__.
+    """
+    next_in_mro = object
+    # Look for the last occurrence of Generic or Generic[...].
+    for i, c in enumerate(cls.__mro__[:-1]):
+        if isinstance(c, GenericMeta) and c._gorg is Generic:
+            next_in_mro = cls.__mro__[i + 1]
+    return next_in_mro
+
+
+def _make_subclasshook(cls):
+    """Construct a __subclasshook__ callable that incorporates
+    the associated __extra__ class in subclass checks performed
+    against cls.
+    """
+    if isinstance(cls.__extra__, abc.ABCMeta):
+        # The logic mirrors that of ABCMeta.__subclasscheck__.
+        # Registered classes need not be checked here because
+        # cls and its extra share the same _abc_registry.
+        def __extrahook__(cls, subclass):
+            res = cls.__extra__.__subclasshook__(subclass)
+            if res is not NotImplemented:
+                return res
+            if cls.__extra__ in getattr(subclass, '__mro__', ()):
+                return True
+            for scls in cls.__extra__.__subclasses__():
+                if isinstance(scls, GenericMeta):
+                    continue
+                if issubclass(subclass, scls):
+                    return True
+            return NotImplemented
+    else:
+        # For non-ABC extras we'll just call issubclass().
+        def __extrahook__(cls, subclass):
+            if cls.__extra__ and issubclass(subclass, cls.__extra__):
+                return True
+            return NotImplemented
+    return classmethod(__extrahook__)
+
+
+class GenericMeta(TypingMeta, abc.ABCMeta):
+    """Metaclass for generic types.
+
+    This is a metaclass for typing.Generic and generic ABCs defined in
+    typing module. User defined subclasses of GenericMeta can override
+    __new__ and invoke super().__new__. Note that GenericMeta.__new__
+    has strict rules on what is allowed in its bases argument:
+    * plain Generic is disallowed in bases;
+    * Generic[...] should appear in bases at most once;
+    * if Generic[...] is present, then it should list all type variables
+      that appear in other bases.
+    In addition, type of all generic bases is erased, e.g., C[int] is
+    stripped to plain C.
+    """
+
+    def __new__(cls, name, bases, namespace,
+                tvars=None, args=None, origin=None, extra=None, orig_bases=None):
+        """Create a new generic class. GenericMeta.__new__ accepts
+        keyword arguments that are used for internal bookkeeping, therefore
+        an override should pass unused keyword arguments to super().
+        """
+        if tvars is not None:
+            # Called from __getitem__() below.
+            assert origin is not None
+            assert all(isinstance(t, TypeVar) for t in tvars), tvars
+        else:
+            # Called from class statement.
+            assert tvars is None, tvars
+            assert args is None, args
+            assert origin is None, origin
+
+            # Get the full set of tvars from the bases.
+            tvars = _type_vars(bases)
+            # Look for Generic[T1, ..., Tn].
+            # If found, tvars must be a subset of it.
+            # If not found, tvars is it.
+            # Also check for and reject plain Generic,
+            # and reject multiple Generic[...].
+            gvars = None
+            for base in 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 None:
+            extra = namespace.get('__extra__')
+        if extra is not None and type(extra) is abc.ABCMeta and extra not in bases:
+            bases = (extra,) + bases
+        bases = tuple(b._gorg if isinstance(b, GenericMeta) else b for b in bases)
+
+        # remove bare Generic from bases if there are other generic 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)
+        super(GenericMeta, self).__setattr__('_gorg',
+                                             self if not origin else origin._gorg)
+
+        self.__parameters__ = tvars
+        # Be prepared that GenericMeta will be subclassed by TupleMeta
+        # and CallableMeta, those two allow ..., (), or [] in __args___.
+        self.__args__ = tuple(Ellipsis if a is _TypingEllipsis else
+                              () if a is _TypingEmpty else
+                              a for a in args) if args else None
+        # Speed hack (https://github.com/python/typing/issues/196).
+        self.__next_in_mro__ = _next_in_mro(self)
+        # Preserve base classes on subclassing (__bases__ are type erased now).
+        if orig_bases is None:
+            self.__orig_bases__ = initial_bases
+
+        # This allows unparameterized generic collections to be used
+        # with issubclass() and isinstance() in the same way as their
+        # collections.abc counterparts (e.g., isinstance([], Iterable)).
+        if (
+            '__subclasshook__' not in namespace and extra or
+            # allow overriding
+            getattr(self.__subclasshook__, '__name__', '') == '__extrahook__'
+        ):
+            self.__subclasshook__ = _make_subclasshook(self)
+
+        if origin and hasattr(origin, '__qualname__'):  # Fix for Python 3.2.
+            self.__qualname__ = origin.__qualname__
+        self.__tree_hash__ = (hash(self._subs_tree()) if origin else
+                              super(GenericMeta, self).__hash__())
+        return self
+
+    def __init__(self, *args, **kwargs):
+        super(GenericMeta, self).__init__(*args, **kwargs)
+        if isinstance(self.__extra__, abc.ABCMeta):
+            self._abc_registry = self.__extra__._abc_registry
+            self._abc_cache = self.__extra__._abc_cache
+        elif self.__origin__ is not None:
+            self._abc_registry = self.__origin__._abc_registry
+            self._abc_cache = self.__origin__._abc_cache
+
+    # _abc_negative_cache and _abc_negative_cache_version
+    # realised as descriptors, since GenClass[t1, t2, ...] always
+    # share subclass info with GenClass.
+    # This is an important memory optimization.
+    @property
+    def _abc_negative_cache(self):
+        if isinstance(self.__extra__, abc.ABCMeta):
+            return self.__extra__._abc_negative_cache
+        return self._gorg._abc_generic_negative_cache
+
+    @_abc_negative_cache.setter
+    def _abc_negative_cache(self, value):
+        if self.__origin__ is None:
+            if isinstance(self.__extra__, abc.ABCMeta):
+                self.__extra__._abc_negative_cache = value
+            else:
+                self._abc_generic_negative_cache = value
+
+    @property
+    def _abc_negative_cache_version(self):
+        if isinstance(self.__extra__, abc.ABCMeta):
+            return self.__extra__._abc_negative_cache_version
+        return self._gorg._abc_generic_negative_cache_version
+
+    @_abc_negative_cache_version.setter
+    def _abc_negative_cache_version(self, value):
+        if self.__origin__ is None:
+            if isinstance(self.__extra__, abc.ABCMeta):
+                self.__extra__._abc_negative_cache_version = value
+            else:
+                self._abc_generic_negative_cache_version = value
+
+    def _get_type_vars(self, tvars):
+        if self.__origin__ and self.__parameters__:
+            _get_type_vars(self.__parameters__, tvars)
+
+    def _eval_type(self, globalns, localns):
+        ev_origin = (self.__origin__._eval_type(globalns, localns)
+                     if self.__origin__ else None)
+        ev_args = tuple(_eval_type(a, globalns, localns) for a
+                        in self.__args__) if self.__args__ else None
+        if ev_origin == self.__origin__ and ev_args == self.__args__:
+            return self
+        return self.__class__(self.__name__,
+                              self.__bases__,
+                              dict(self.__dict__),
+                              tvars=_type_vars(ev_args) if ev_args else None,
+                              args=ev_args,
+                              origin=ev_origin,
+                              extra=self.__extra__,
+                              orig_bases=self.__orig_bases__)
+
+    def __repr__(self):
+        if self.__origin__ is None:
+            return super(GenericMeta, self).__repr__()
+        return self._tree_repr(self._subs_tree())
+
+    def _tree_repr(self, tree):
+        arg_list = []
+        for arg in tree[1:]:
+            if arg == ():
+                arg_list.append('()')
+            elif not isinstance(arg, tuple):
+                arg_list.append(_type_repr(arg))
+            else:
+                arg_list.append(arg[0]._tree_repr(arg))
+        return super(GenericMeta, self).__repr__() + '[%s]' % ', '.join(arg_list)
+
+    def _subs_tree(self, tvars=None, args=None):
+        if self.__origin__ is None:
+            return self
+        tree_args = _subs_tree(self, tvars, args)
+        return (self._gorg,) + tuple(tree_args)
+
+    def __eq__(self, other):
+        if not isinstance(other, GenericMeta):
+            return NotImplemented
+        if self.__origin__ is None or other.__origin__ is None:
+            return self is other
+        return self.__tree_hash__ == other.__tree_hash__
+
+    def __hash__(self):
+        return self.__tree_hash__
+
+    @_tp_cache
+    def __getitem__(self, params):
+        if not isinstance(params, tuple):
+            params = (params,)
+        if not params and self._gorg is not Tuple:
+            raise TypeError(
+                "Parameter list to %s[...] cannot be empty" % _qualname(self))
+        msg = "Parameters to generic types must be types."
+        params = tuple(_type_check(p, msg) for p in params)
+        if self in (Generic, Protocol):
+            # Generic can only be subscripted with unique type variables.
+            if not all(isinstance(p, TypeVar) for p in params):
+                raise TypeError(
+                    "Parameters to %s[...] must all be type variables" % self.__name__)
+            if len(set(params)) != len(params):
+                raise TypeError(
+                    "Parameters to %s[...] must all be unique" % self.__name__)
+            tvars = params
+            args = params
+        elif self in (Tuple, Callable):
+            tvars = _type_vars(params)
+            args = params
+        elif self.__origin__ in (Generic, Protocol):
+            # Can't subscript Generic[...] or Protocol[...].
+            raise TypeError("Cannot subscript already-subscripted %s" %
+                            repr(self))
+        else:
+            # Subscripting a regular Generic subclass.
+            _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__,
+                              dict(self.__dict__),
+                              tvars=tvars,
+                              args=args,
+                              origin=self,
+                              extra=self.__extra__,
+                              orig_bases=self.__orig_bases__)
+
+    def __subclasscheck__(self, cls):
+        if self.__origin__ is not None:
+            # These should only be modules within the standard library.
+            # singledispatch is an exception, because it's a Python 2 backport
+            # of functools.singledispatch.
+            whitelist = ['abc', 'functools', 'singledispatch']
+            if (sys._getframe(1).f_globals['__name__'] in whitelist or
+                    # The second frame is needed for the case where we came
+                    # from _ProtocolMeta.__subclasscheck__.
+                    sys._getframe(2).f_globals['__name__'] in whitelist):
+                return False
+            raise TypeError("Parameterized generics cannot be used with class "
+                            "or instance checks")
+        if self is Generic:
+            raise TypeError("Class %r cannot be used with class "
+                            "or instance checks" % self)
+        return super(GenericMeta, self).__subclasscheck__(cls)
+
+    def __instancecheck__(self, instance):
+        # Since we extend ABC.__subclasscheck__ and
+        # ABC.__instancecheck__ inlines the cache checking done by the
+        # latter, we must extend __instancecheck__ too. For simplicity
+        # we just skip the cache check -- instance checks for generic
+        # classes are supposed to be rare anyways.
+        if hasattr(instance, "__class__"):
+            return issubclass(instance.__class__, self)
+        return False
+
+    def __setattr__(self, attr, value):
+        # We consider all the subscripted genrics as proxies for original class
+        if (
+            attr.startswith('__') and attr.endswith('__') or
+            attr.startswith('_abc_')
+        ):
+            super(GenericMeta, self).__setattr__(attr, value)
+        else:
+            super(GenericMeta, self._gorg).__setattr__(attr, value)
+
+
+def _copy_generic(self):
+    """Hack to work around https://bugs.python.org/issue11480 on Python 2"""
+    return self.__class__(self.__name__, self.__bases__, dict(self.__dict__),
+                          self.__parameters__, self.__args__, self.__origin__,
+                          self.__extra__, self.__orig_bases__)
+
+
+copy._copy_dispatch[GenericMeta] = _copy_generic
+
+
+# Prevent checks for Generic to crash when defining Generic.
+Generic = None
+
+
+def _generic_new(base_cls, cls, *args, **kwds):
+    # Assure type is erased on instantiation,
+    # but attempt to store it in __orig_class__
+    if cls.__origin__ is None:
+        if (base_cls.__new__ is object.__new__ and
+                cls.__init__ is not object.__init__):
+            return base_cls.__new__(cls)
+        else:
+            return base_cls.__new__(cls, *args, **kwds)
+    else:
+        origin = cls._gorg
+        if (base_cls.__new__ is object.__new__ and
+                cls.__init__ is not object.__init__):
+            obj = base_cls.__new__(origin)
+        else:
+            obj = base_cls.__new__(origin, *args, **kwds)
+        try:
+            obj.__orig_class__ = cls
+        except AttributeError:
+            pass
+        obj.__init__(*args, **kwds)
+        return obj
+
+
+class Generic(object):
+    """Abstract base class for generic types.
+
+    A generic type is typically declared by inheriting from
+    this class parameterized with one or more type variables.
+    For example, a generic mapping type might be defined as::
+
+      class Mapping(Generic[KT, VT]):
+          def __getitem__(self, key: KT) -> VT:
+              ...
+          # Etc.
+
+    This class can then be used as follows::
+
+      def lookup_name(mapping: Mapping[KT, VT], key: KT, default: VT) -> VT:
+          try:
+              return mapping[key]
+          except KeyError:
+              return default
+    """
+
+    __metaclass__ = GenericMeta
+    __slots__ = ()
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is Generic:
+            raise TypeError("Type Generic cannot be instantiated; "
+                            "it can be used only as a base class")
+        return _generic_new(cls.__next_in_mro__, cls, *args, **kwds)
+
+
+class _TypingEmpty(object):
+    """Internal placeholder for () or []. Used by TupleMeta and CallableMeta
+    to allow empty list/tuple in specific places, without allowing them
+    to sneak in where prohibited.
+    """
+
+
+class _TypingEllipsis(object):
+    """Internal placeholder for ... (ellipsis)."""
+
+
+class TupleMeta(GenericMeta):
+    """Metaclass for Tuple (internal)."""
+
+    @_tp_cache
+    def __getitem__(self, parameters):
+        if self.__origin__ is not None or self._gorg is not Tuple:
+            # Normal generic rules apply if this is not the first subscription
+            # or a subscription of a subclass.
+            return super(TupleMeta, self).__getitem__(parameters)
+        if parameters == ():
+            return super(TupleMeta, self).__getitem__((_TypingEmpty,))
+        if not isinstance(parameters, tuple):
+            parameters = (parameters,)
+        if len(parameters) == 2 and parameters[1] is Ellipsis:
+            msg = "Tuple[t, ...]: t must be a type."
+            p = _type_check(parameters[0], msg)
+            return super(TupleMeta, self).__getitem__((p, _TypingEllipsis))
+        msg = "Tuple[t0, t1, ...]: each t must be a type."
+        parameters = tuple(_type_check(p, msg) for p in parameters)
+        return super(TupleMeta, self).__getitem__(parameters)
+
+    def __instancecheck__(self, obj):
+        if self.__args__ is None:
+            return isinstance(obj, tuple)
+        raise TypeError("Parameterized Tuple cannot be used "
+                        "with isinstance().")
+
+    def __subclasscheck__(self, cls):
+        if self.__args__ is None:
+            return issubclass(cls, tuple)
+        raise TypeError("Parameterized Tuple cannot be used "
+                        "with issubclass().")
+
+
+copy._copy_dispatch[TupleMeta] = _copy_generic
+
+
+class Tuple(tuple):
+    """Tuple type; Tuple[X, Y] is the cross-product type of X and Y.
+
+    Example: Tuple[T1, T2] is a tuple of two elements corresponding
+    to type variables T1 and T2.  Tuple[int, float, str] is a tuple
+    of an int, a float and a string.
+
+    To specify a variable-length tuple of homogeneous type, use Tuple[T, ...].
+    """
+
+    __metaclass__ = TupleMeta
+    __extra__ = tuple
+    __slots__ = ()
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is Tuple:
+            raise TypeError("Type Tuple cannot be instantiated; "
+                            "use tuple() instead")
+        return _generic_new(tuple, cls, *args, **kwds)
+
+
+class CallableMeta(GenericMeta):
+    """ Metaclass for Callable."""
+
+    def __repr__(self):
+        if self.__origin__ is None:
+            return super(CallableMeta, self).__repr__()
+        return self._tree_repr(self._subs_tree())
+
+    def _tree_repr(self, tree):
+        if self._gorg is not Callable:
+            return super(CallableMeta, self)._tree_repr(tree)
+        # For actual Callable (not its subclass) we override
+        # super(CallableMeta, self)._tree_repr() for nice formatting.
+        arg_list = []
+        for arg in tree[1:]:
+            if not isinstance(arg, tuple):
+                arg_list.append(_type_repr(arg))
+            else:
+                arg_list.append(arg[0]._tree_repr(arg))
+        if arg_list[0] == '...':
+            return repr(tree[0]) + '[..., %s]' % arg_list[1]
+        return (repr(tree[0]) +
+                '[[%s], %s]' % (', '.join(arg_list[:-1]), arg_list[-1]))
+
+    def __getitem__(self, parameters):
+        """A thin wrapper around __getitem_inner__ to provide the latter
+        with hashable arguments to improve speed.
+        """
+
+        if self.__origin__ is not None or self._gorg is not Callable:
+            return super(CallableMeta, self).__getitem__(parameters)
+        if not isinstance(parameters, tuple) or len(parameters) != 2:
+            raise TypeError("Callable must be used as "
+                            "Callable[[arg, ...], result].")
+        args, result = parameters
+        if args is Ellipsis:
+            parameters = (Ellipsis, result)
+        else:
+            if not isinstance(args, list):
+                raise TypeError("Callable[args, result]: args must be a list."
+                                " Got %.100r." % (args,))
+            parameters = (tuple(args), result)
+        return self.__getitem_inner__(parameters)
+
+    @_tp_cache
+    def __getitem_inner__(self, parameters):
+        args, result = parameters
+        msg = "Callable[args, result]: result must be a type."
+        result = _type_check(result, msg)
+        if args is Ellipsis:
+            return super(CallableMeta, self).__getitem__((_TypingEllipsis, result))
+        msg = "Callable[[arg, ...], result]: each arg must be a type."
+        args = tuple(_type_check(arg, msg) for arg in args)
+        parameters = args + (result,)
+        return super(CallableMeta, self).__getitem__(parameters)
+
+
+copy._copy_dispatch[CallableMeta] = _copy_generic
+
+
+class Callable(object):
+    """Callable type; Callable[[int], str] is a function of (int) -> str.
+
+    The subscription syntax must always be used with exactly two
+    values: the argument list and the return type.  The argument list
+    must be a list of types or ellipsis; the return type must be a single type.
+
+    There is no syntax to indicate optional or keyword arguments,
+    such function types are rarely used as callback types.
+    """
+
+    __metaclass__ = CallableMeta
+    __extra__ = collections_abc.Callable
+    __slots__ = ()
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is Callable:
+            raise TypeError("Type Callable cannot be instantiated; "
+                            "use a non-abstract subclass instead")
+        return _generic_new(cls.__next_in_mro__, cls, *args, **kwds)
+
+
+def cast(typ, val):
+    """Cast a value to a type.
+
+    This returns the value unchanged.  To the type checker this
+    signals that the return value has the designated type, but at
+    runtime we intentionally don't check anything (we want this
+    to be as fast as possible).
+    """
+    return val
+
+
+def _get_defaults(func):
+    """Internal helper to extract the default arguments, by name."""
+    code = func.__code__
+    pos_count = code.co_argcount
+    arg_names = code.co_varnames
+    arg_names = arg_names[:pos_count]
+    defaults = func.__defaults__ or ()
+    kwdefaults = func.__kwdefaults__
+    res = dict(kwdefaults) if kwdefaults else {}
+    pos_offset = pos_count - len(defaults)
+    for name, value in zip(arg_names[pos_offset:], defaults):
+        assert name not in res
+        res[name] = value
+    return res
+
+
+def get_type_hints(obj, globalns=None, localns=None):
+    """In Python 2 this is not supported and always returns None."""
+    return None
+
+
+def no_type_check(arg):
+    """Decorator to indicate that annotations are not type hints.
+
+    The argument must be a class or function; if it is a class, it
+    applies recursively to all methods and classes defined in that class
+    (but not to methods defined in its superclasses or subclasses).
+
+    This mutates the function(s) or class(es) in place.
+    """
+    if isinstance(arg, type):
+        arg_attrs = arg.__dict__.copy()
+        for attr, val in arg.__dict__.items():
+            if val in arg.__bases__ + (arg,):
+                arg_attrs.pop(attr)
+        for obj in arg_attrs.values():
+            if isinstance(obj, types.FunctionType):
+                obj.__no_type_check__ = True
+            if isinstance(obj, type):
+                no_type_check(obj)
+    try:
+        arg.__no_type_check__ = True
+    except TypeError:  # built-in classes
+        pass
+    return arg
+
+
+def no_type_check_decorator(decorator):
+    """Decorator to give another decorator the @no_type_check effect.
+
+    This wraps the decorator with something that wraps the decorated
+    function in @no_type_check.
+    """
+
+    @functools.wraps(decorator)
+    def wrapped_decorator(*args, **kwds):
+        func = decorator(*args, **kwds)
+        func = no_type_check(func)
+        return func
+
+    return wrapped_decorator
+
+
+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
+
+
+_PROTO_WHITELIST = ['Callable', 'Iterable', 'Iterator',
+                    'Hashable', 'Sized', 'Container', 'Collection',
+                    'Reversible', 'ContextManager']
+
+
+class _ProtocolMeta(GenericMeta):
+    """Internal metaclass for Protocol.
+
+    This exists so Protocol classes can be generic without deriving
+    from Generic.
+    """
+    def __init__(cls, *args, **kwargs):
+        super(_ProtocolMeta, cls).__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__ == '_abcoll' 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)
+            cls._callable_members_only = all(callable(getattr(cls, attr))
+                                             for attr in cls._get_protocol_attrs())
+
+            def _no_init(self, *args, **kwargs):
+                if type(self)._is_protocol:
+                    raise TypeError('Protocols cannot be instantiated')
+            cls.__init__ = _no_init
+
+        def _proto_hook(cls, other):
+            if not cls.__dict__.get('_is_protocol', None):
+                return NotImplemented
+            if not isinstance(other, type):
+                # Similar error as for issubclass(1, int)
+                # (also not a chance for old-style classes)
+                raise TypeError('issubclass() arg 1 must be a new-style class')
+            for attr in cls._get_protocol_attrs():
+                for base in other.__mro__:
+                    if attr in base.__dict__:
+                        if base.__dict__[attr] is None:
+                            return NotImplemented
+                        break
+                else:
+                    return NotImplemented
+            return True
+        if '__subclasshook__' not in cls.__dict__:
+            cls.__subclasshook__ = classmethod(_proto_hook)
+
+    def __instancecheck__(self, instance):
+        # We need this method for situations where attributes are assigned in __init__
+        if isinstance(instance, type):
+            # This looks like a fundamental limitation of Python 2.
+            # It cannot support runtime protocol metaclasses, On Python 2 classes
+            # cannot be correctly inspected as instances of protocols.
+            return False
+        if ((not getattr(self, '_is_protocol', False) or
+                self._callable_members_only) and
+                issubclass(instance.__class__, self)):
+            return True
+        if self._is_protocol:
+            if all(hasattr(instance, attr) and
+                    (not callable(getattr(self, attr)) or
+                     getattr(instance, attr) is not None)
+                    for attr in self._get_protocol_attrs()):
+                return True
+        return super(GenericMeta, self).__instancecheck__(instance)
+
+    def __subclasscheck__(self, cls):
+        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'] or
+                    # This is needed because we remove subclasses from unions on Python 2.
+                    sys._getframe(2).f_globals['__name__'] == 'typing'):
+                return False
+            raise TypeError("Instance and class checks can only be used with"
+                            " @runtime_checkable protocols")
+        if (self.__dict__.get('_is_runtime_protocol', None) and
+                not self._callable_members_only):
+            if sys._getframe(1).f_globals['__name__'] in ['abc', 'functools']:
+                return super(GenericMeta, self).__subclasscheck__(cls)
+            raise TypeError("Protocols with non-method members"
+                            " don't support issubclass()")
+        return super(_ProtocolMeta, self).__subclasscheck__(cls)
+
+    def _get_protocol_attrs(self):
+        attrs = set()
+        for base in self.__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__', '_get_protocol_attrs',
+                        '__next_in_mro__', '__parameters__', '__origin__',
+                        '__orig_bases__', '__extra__', '__tree_hash__',
+                        '__doc__', '__subclasshook__', '__init__', '__new__',
+                        '__module__', '_MutableMapping__marker',
+                        '__metaclass__', '_gorg', '_callable_members_only')):
+                    attrs.add(attr)
+        return attrs
+
+
+class Protocol(object):
+    """Base class for protocol classes. Protocol classes are defined as::
+
+      class Proto(Protocol):
+          def meth(self):
+              # type: () -> int
+              pass
+
+    Such classes are primarily used with static type checkers that recognize
+    structural subtyping (static duck-typing), for example::
+
+      class C:
+          def meth(self):
+              # type: () -> int
+              return 0
+
+      def func(x):
+          # type: (Proto) -> int
+          return x.meth()
+
+      func(C())  # Passes static type check
+
+    See PEP 544 for details. Protocol classes decorated with @typing.runtime_checkable
+    act as simple-minded runtime protocols that 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):
+              # type: () -> T
+              pass
+    """
+
+    __metaclass__ = _ProtocolMeta
+    __slots__ = ()
+    _is_protocol = True
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is Protocol:
+            raise TypeError("Type Protocol cannot be instantiated; "
+                            "it can be used only as a base class")
+        return _generic_new(cls.__next_in_mro__, cls, *args, **kwds)
+
+
+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
+
+
+# Various ABCs mimicking those in collections.abc.
+# A few are simply re-exported for completeness.
+
+Hashable = collections_abc.Hashable  # Not generic.
+
+
+class Iterable(Generic[T_co]):
+    __slots__ = ()
+    __extra__ = collections_abc.Iterable
+
+
+class Iterator(Iterable[T_co]):
+    __slots__ = ()
+    __extra__ = collections_abc.Iterator
+
+
+@runtime_checkable
+class SupportsInt(Protocol):
+    __slots__ = ()
+
+    @abstractmethod
+    def __int__(self):
+        pass
+
+
+@runtime_checkable
+class SupportsFloat(Protocol):
+    __slots__ = ()
+
+    @abstractmethod
+    def __float__(self):
+        pass
+
+
+@runtime_checkable
+class SupportsComplex(Protocol):
+    __slots__ = ()
+
+    @abstractmethod
+    def __complex__(self):
+        pass
+
+
+@runtime_checkable
+class SupportsIndex(Protocol):
+    __slots__ = ()
+
+    @abstractmethod
+    def __index__(self):
+        pass
+
+
+@runtime_checkable
+class SupportsAbs(Protocol[T_co]):
+    __slots__ = ()
+
+    @abstractmethod
+    def __abs__(self):
+        pass
+
+
+if hasattr(collections_abc, 'Reversible'):
+    class Reversible(Iterable[T_co]):
+        __slots__ = ()
+        __extra__ = collections_abc.Reversible
+else:
+    @runtime_checkable
+    class Reversible(Protocol[T_co]):
+        __slots__ = ()
+
+        @abstractmethod
+        def __reversed__(self):
+            pass
+
+
+Sized = collections_abc.Sized  # Not generic.
+
+
+class Container(Generic[T_co]):
+    __slots__ = ()
+    __extra__ = collections_abc.Container
+
+
+# Callable was defined earlier.
+
+
+class AbstractSet(Sized, Iterable[T_co], Container[T_co]):
+    __slots__ = ()
+    __extra__ = collections_abc.Set
+
+
+class MutableSet(AbstractSet[T]):
+    __slots__ = ()
+    __extra__ = collections_abc.MutableSet
+
+
+# NOTE: It is only covariant in the value type.
+class Mapping(Sized, Iterable[KT], Container[KT], Generic[KT, VT_co]):
+    __slots__ = ()
+    __extra__ = collections_abc.Mapping
+
+
+class MutableMapping(Mapping[KT, VT]):
+    __slots__ = ()
+    __extra__ = collections_abc.MutableMapping
+
+
+if hasattr(collections_abc, 'Reversible'):
+    class Sequence(Sized, Reversible[T_co], Container[T_co]):
+        __slots__ = ()
+        __extra__ = collections_abc.Sequence
+else:
+    class Sequence(Sized, Iterable[T_co], Container[T_co]):
+        __slots__ = ()
+        __extra__ = collections_abc.Sequence
+
+
+class MutableSequence(Sequence[T]):
+    __slots__ = ()
+    __extra__ = collections_abc.MutableSequence
+
+
+class ByteString(Sequence[int]):
+    pass
+
+
+ByteString.register(str)
+ByteString.register(bytearray)
+
+
+class List(list, MutableSequence[T]):
+    __slots__ = ()
+    __extra__ = list
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is List:
+            raise TypeError("Type List cannot be instantiated; "
+                            "use list() instead")
+        return _generic_new(list, cls, *args, **kwds)
+
+
+class Deque(collections.deque, MutableSequence[T]):
+    __slots__ = ()
+    __extra__ = collections.deque
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is Deque:
+            return collections.deque(*args, **kwds)
+        return _generic_new(collections.deque, cls, *args, **kwds)
+
+
+class Set(set, MutableSet[T]):
+    __slots__ = ()
+    __extra__ = set
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is Set:
+            raise TypeError("Type Set cannot be instantiated; "
+                            "use set() instead")
+        return _generic_new(set, cls, *args, **kwds)
+
+
+class FrozenSet(frozenset, AbstractSet[T_co]):
+    __slots__ = ()
+    __extra__ = frozenset
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is FrozenSet:
+            raise TypeError("Type FrozenSet cannot be instantiated; "
+                            "use frozenset() instead")
+        return _generic_new(frozenset, cls, *args, **kwds)
+
+
+class MappingView(Sized, Iterable[T_co]):
+    __slots__ = ()
+    __extra__ = collections_abc.MappingView
+
+
+class KeysView(MappingView[KT], AbstractSet[KT]):
+    __slots__ = ()
+    __extra__ = collections_abc.KeysView
+
+
+class ItemsView(MappingView[Tuple[KT, VT_co]],
+                AbstractSet[Tuple[KT, VT_co]],
+                Generic[KT, VT_co]):
+    __slots__ = ()
+    __extra__ = collections_abc.ItemsView
+
+
+class ValuesView(MappingView[VT_co]):
+    __slots__ = ()
+    __extra__ = collections_abc.ValuesView
+
+
+class ContextManager(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
+
+
+class Dict(dict, MutableMapping[KT, VT]):
+    __slots__ = ()
+    __extra__ = dict
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is Dict:
+            raise TypeError("Type Dict cannot be instantiated; "
+                            "use dict() instead")
+        return _generic_new(dict, cls, *args, **kwds)
+
+
+class DefaultDict(collections.defaultdict, MutableMapping[KT, VT]):
+    __slots__ = ()
+    __extra__ = collections.defaultdict
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is DefaultDict:
+            return collections.defaultdict(*args, **kwds)
+        return _generic_new(collections.defaultdict, cls, *args, **kwds)
+
+
+class Counter(collections.Counter, Dict[T, int]):
+    __slots__ = ()
+    __extra__ = collections.Counter
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is Counter:
+            return collections.Counter(*args, **kwds)
+        return _generic_new(collections.Counter, cls, *args, **kwds)
+
+
+# Determine what base class to use for Generator.
+if hasattr(collections_abc, 'Generator'):
+    # Sufficiently recent versions of 3.5 have a Generator ABC.
+    _G_base = collections_abc.Generator
+else:
+    # Fall back on the exact type.
+    _G_base = types.GeneratorType
+
+
+class Generator(Iterator[T_co], Generic[T_co, T_contra, V_co]):
+    __slots__ = ()
+    __extra__ = _G_base
+
+    def __new__(cls, *args, **kwds):
+        if cls._gorg is Generator:
+            raise TypeError("Type Generator cannot be instantiated; "
+                            "create a subclass instead")
+        return _generic_new(_G_base, cls, *args, **kwds)
+
+
+# Internal type variable used for Type[].
+CT_co = TypeVar('CT_co', covariant=True, bound=type)
+
+
+# This is not a real generic class.  Don't use outside annotations.
+class Type(Generic[CT_co]):
+    """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__ = ()
+    __extra__ = type
+
+
+def NamedTuple(typename, fields):
+    """Typed version of namedtuple.
+
+    Usage::
+
+        Employee = typing.NamedTuple('Employee', [('name', str), ('id', int)])
+
+    This is equivalent to::
+
+        Employee = collections.namedtuple('Employee', ['name', 'id'])
+
+    The resulting class has one extra attribute: _field_types,
+    giving a dict mapping field names to types.  (The field names
+    are in the _fields attribute, which is part of the namedtuple
+    API.)
+    """
+    fields = [(n, t) for n, t in fields]
+    cls = collections.namedtuple(typename, [n for n, t in fields])
+    cls._field_types = dict(fields)
+    # Set the module to the caller's module (otherwise it'd be 'typing').
+    try:
+        cls.__module__ = sys._getframe(1).f_globals.get('__name__', '__main__')
+    except (AttributeError, ValueError):
+        pass
+    return cls
+
+
+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(cls, *args, **kwargs):
+    return dict(*args, **kwargs)
+
+
+def _typeddict_new(cls, _typename, _fields=None, **kwargs):
+    total = kwargs.pop('total', True)
+    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)
+
+
+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 == b'TypedDict' else _dict_new
+        tp_dict = super(_TypedDictMeta, cls).__new__(cls, name, (dict,), ns)
+
+        anns = ns.get('__annotations__', {})
+        msg = "TypedDict('Name', {f0: t0, f1: t1, ...}); each t must be a type"
+        anns = {n: _type_check(tp, msg) for n, tp in anns.items()}
+        for base in bases:
+            anns.update(base.__dict__.get('__annotations__', {}))
+        tp_dict.__annotations__ = anns
+        if not hasattr(tp_dict, '__total__'):
+            tp_dict.__total__ = total
+        return tp_dict
+
+    __instancecheck__ = __subclasscheck__ = _check_fails
+
+
+TypedDict = _TypedDictMeta(b'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::
+
+        Point2D = TypedDict('Point2D', {'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 could be accessed via Point2D.__annotations__. TypedDict
+    supports an additional equivalent form::
+
+        Point2D = TypedDict('Point2D', x=int, y=int, label=str)
+    """
+
+
+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):
+            # type: (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
+
+    # Some versions of Python 2 complain because of making all strings unicode
+    new_type.__name__ = str(name)
+    new_type.__supertype__ = tp
+    return new_type
+
+
+# Python-version-specific alias (Python 2: unicode; Python 3: str)
+Text = unicode
+
+
+# Constant that's True when type checking, but False here.
+TYPE_CHECKING = False
+
+
+class IO(Generic[AnyStr]):
+    """Generic base class for TextIO and BinaryIO.
+
+    This is an abstract, generic version of the return of open().
+
+    NOTE: This does not distinguish between the different possible
+    classes (text vs. binary, read vs. write vs. read/write,
+    append-only, unbuffered).  The TextIO and BinaryIO subclasses
+    below capture the distinctions between text vs. binary, which is
+    pervasive in the interface; however we currently do not offer a
+    way to track the other distinctions in the type system.
+    """
+
+    __slots__ = ()
+
+    @abstractproperty
+    def mode(self):
+        pass
+
+    @abstractproperty
+    def name(self):
+        pass
+
+    @abstractmethod
+    def close(self):
+        pass
+
+    @abstractproperty
+    def closed(self):
+        pass
+
+    @abstractmethod
+    def fileno(self):
+        pass
+
+    @abstractmethod
+    def flush(self):
+        pass
+
+    @abstractmethod
+    def isatty(self):
+        pass
+
+    @abstractmethod
+    def read(self, n=-1):
+        pass
+
+    @abstractmethod
+    def readable(self):
+        pass
+
+    @abstractmethod
+    def readline(self, limit=-1):
+        pass
+
+    @abstractmethod
+    def readlines(self, hint=-1):
+        pass
+
+    @abstractmethod
+    def seek(self, offset, whence=0):
+        pass
+
+    @abstractmethod
+    def seekable(self):
+        pass
+
+    @abstractmethod
+    def tell(self):
+        pass
+
+    @abstractmethod
+    def truncate(self, size=None):
+        pass
+
+    @abstractmethod
+    def writable(self):
+        pass
+
+    @abstractmethod
+    def write(self, s):
+        pass
+
+    @abstractmethod
+    def writelines(self, lines):
+        pass
+
+    @abstractmethod
+    def __enter__(self):
+        pass
+
+    @abstractmethod
+    def __exit__(self, type, value, traceback):
+        pass
+
+
+class BinaryIO(IO[bytes]):
+    """Typed version of the return of open() in binary mode."""
+
+    __slots__ = ()
+
+    @abstractmethod
+    def write(self, s):
+        pass
+
+    @abstractmethod
+    def __enter__(self):
+        pass
+
+
+class TextIO(IO[unicode]):
+    """Typed version of the return of open() in text mode."""
+
+    __slots__ = ()
+
+    @abstractproperty
+    def buffer(self):
+        pass
+
+    @abstractproperty
+    def encoding(self):
+        pass
+
+    @abstractproperty
+    def errors(self):
+        pass
+
+    @abstractproperty
+    def line_buffering(self):
+        pass
+
+    @abstractproperty
+    def newlines(self):
+        pass
+
+    @abstractmethod
+    def __enter__(self):
+        pass
+
+
+class io(object):
+    """Wrapper namespace for IO generic classes."""
+
+    __all__ = ['IO', 'TextIO', 'BinaryIO']
+    IO = IO
+    TextIO = TextIO
+    BinaryIO = BinaryIO
+
+
+io.__name__ = __name__ + b'.io'
+sys.modules[io.__name__] = io
+
+
+Pattern = _TypeAlias('Pattern', AnyStr, type(stdlib_re.compile('')),
+                     lambda p: p.pattern)
+Match = _TypeAlias('Match', AnyStr, type(stdlib_re.match('', '')),
+                   lambda m: m.re.pattern)
+
+
+class re(object):
+    """Wrapper namespace for re type aliases."""
+
+    __all__ = ['Pattern', 'Match']
+    Pattern = Pattern
+    Match = Match
+
+
+re.__name__ = __name__ + b'.re'
+sys.modules[re.__name__] = re