text: # Copyright 2007 Google, Inc. All Rights Reserved.
  # Licensed to PSF under a Contributor Agreement.
  
  """Abstract Base Classes (ABCs) for collections, according to PEP 3119.
  
  Unit tests are in test_collections.
  """
  
  from abc import ABCMeta, abstractmethod
  import sys
  
  GenericAlias = type(list[int])
  EllipsisType = type(...)
  def _f(): pass
  FunctionType = type(_f)
  del _f
  
  __all__ = ["Awaitable", "Coroutine",
             "AsyncIterable", "AsyncIterator", "AsyncGenerator",
             "Hashable", "Iterable", "Iterator", "Generator", "Reversible",
             "Sized", "Container", "Callable", "Collection",
             "Set", "MutableSet",
             "Mapping", "MutableMapping",
             "MappingView", "KeysView", "ItemsView", "ValuesView",
             "Sequence", "MutableSequence",
             "ByteString",
             ]
  
  # This module has been renamed from collections.abc to _collections_abc to
  # speed up interpreter startup. Some of the types such as MutableMapping are
  # required early but collections module imports a lot of other modules.
  # See issue #19218
  __name__ = "collections.abc"
  
  # Private list of types that we want to register with the various ABCs
  # so that they will pass tests like:
  #       it = iter(somebytearray)
  #       assert isinstance(it, Iterable)
  # Note:  in other implementations, these types might not be distinct
  # and they may have their own implementation specific types that
  # are not included on this list.
  bytes_iterator = type(iter(b''))
  bytearray_iterator = type(iter(bytearray()))
  #callable_iterator = ???
  dict_keyiterator = type(iter({}.keys()))
  dict_valueiterator = type(iter({}.values()))
  dict_itemiterator = type(iter({}.items()))
  list_iterator = type(iter([]))
  list_reverseiterator = type(iter(reversed([])))
  range_iterator = type(iter(range(0)))
  longrange_iterator = type(iter(range(1 << 1000)))
  set_iterator = type(iter(set()))
  str_iterator = type(iter(""))
  tuple_iterator = type(iter(()))
  zip_iterator = type(iter(zip()))
  ## views ##
  dict_keys = type({}.keys())
  dict_values = type({}.values())
  dict_items = type({}.items())
  ## misc ##
  mappingproxy = type(type.__dict__)
  generator = type((lambda: (yield))())
  ## coroutine ##
  async def _coro(): pass
  _coro = _coro()
  coroutine = type(_coro)
  _coro.close()  # Prevent ResourceWarning
  del _coro
  ## asynchronous generator ##
  async def _ag(): yield
  _ag = _ag()
  async_generator = type(_ag)
  del _ag
  
  
  ### ONE-TRICK PONIES ###
  
  def _check_methods(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
  
  class Hashable(metaclass=ABCMeta):
  
      __slots__ = ()
  
      @abstractmethod
      def __hash__(self):
          return 0
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Hashable:
              return _check_methods(C, "__hash__")
          return NotImplemented
  
  
  class Awaitable(metaclass=ABCMeta):
  
      __slots__ = ()
  
      @abstractmethod
      def __await__(self):
          yield
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Awaitable:
              return _check_methods(C, "__await__")
          return NotImplemented
  
      __class_getitem__ = classmethod(GenericAlias)
  
  
  class Coroutine(Awaitable):
  
      __slots__ = ()
  
      @abstractmethod
      def send(self, value):
          """Send a value into the coroutine.
          Return next yielded value or raise StopIteration.
          """
          raise StopIteration
  
      @abstractmethod
      def throw(self, typ, val=None, tb=None):
          """Raise an exception in the coroutine.
          Return next yielded value or raise StopIteration.
          """
          if val is None:
              if tb is None:
                  raise typ
              val = typ()
          if tb is not None:
              val = val.with_traceback(tb)
          raise val
  
      def close(self):
          """Raise GeneratorExit inside coroutine.
          """
          try:
              self.throw(GeneratorExit)
          except (GeneratorExit, StopIteration):
              pass
          else:
              raise RuntimeError("coroutine ignored GeneratorExit")
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Coroutine:
              return _check_methods(C, '__await__', 'send', 'throw', 'close')
          return NotImplemented
  
  
  Coroutine.register(coroutine)
  
  
  class AsyncIterable(metaclass=ABCMeta):
  
      __slots__ = ()
  
      @abstractmethod
      def __aiter__(self):
          return AsyncIterator()
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is AsyncIterable:
              return _check_methods(C, "__aiter__")
          return NotImplemented
  
      __class_getitem__ = classmethod(GenericAlias)
  
  
  class AsyncIterator(AsyncIterable):
  
      __slots__ = ()
  
      @abstractmethod
      async def __anext__(self):
          """Return the next item or raise StopAsyncIteration when exhausted."""
          raise StopAsyncIteration
  
      def __aiter__(self):
          return self
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is AsyncIterator:
              return _check_methods(C, "__anext__", "__aiter__")
          return NotImplemented
  
  
  class AsyncGenerator(AsyncIterator):
  
      __slots__ = ()
  
      async def __anext__(self):
          """Return the next item from the asynchronous generator.
          When exhausted, raise StopAsyncIteration.
          """
          return await self.asend(None)
  
      @abstractmethod
      async def asend(self, value):
          """Send a value into the asynchronous generator.
          Return next yielded value or raise StopAsyncIteration.
          """
          raise StopAsyncIteration
  
      @abstractmethod
      async def athrow(self, typ, val=None, tb=None):
          """Raise an exception in the asynchronous generator.
          Return next yielded value or raise StopAsyncIteration.
          """
          if val is None:
              if tb is None:
                  raise typ
              val = typ()
          if tb is not None:
              val = val.with_traceback(tb)
          raise val
  
      async def aclose(self):
          """Raise GeneratorExit inside coroutine.
          """
          try:
              await self.athrow(GeneratorExit)
          except (GeneratorExit, StopAsyncIteration):
              pass
          else:
              raise RuntimeError("asynchronous generator ignored GeneratorExit")
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is AsyncGenerator:
              return _check_methods(C, '__aiter__', '__anext__',
                                    'asend', 'athrow', 'aclose')
          return NotImplemented
  
  
  AsyncGenerator.register(async_generator)
  
  
  class Iterable(metaclass=ABCMeta):
  
      __slots__ = ()
  
      @abstractmethod
      def __iter__(self):
          while False:
              yield None
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Iterable:
              return _check_methods(C, "__iter__")
          return NotImplemented
  
      __class_getitem__ = classmethod(GenericAlias)
  
  
  class Iterator(Iterable):
  
      __slots__ = ()
  
      @abstractmethod
      def __next__(self):
          'Return the next item from the iterator. When exhausted, raise StopIteration'
          raise StopIteration
  
      def __iter__(self):
          return self
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Iterator:
              return _check_methods(C, '__iter__', '__next__')
          return NotImplemented
  
  
  Iterator.register(bytes_iterator)
  Iterator.register(bytearray_iterator)
  #Iterator.register(callable_iterator)
  Iterator.register(dict_keyiterator)
  Iterator.register(dict_valueiterator)
  Iterator.register(dict_itemiterator)
  Iterator.register(list_iterator)
  Iterator.register(list_reverseiterator)
  Iterator.register(range_iterator)
  Iterator.register(longrange_iterator)
  Iterator.register(set_iterator)
  Iterator.register(str_iterator)
  Iterator.register(tuple_iterator)
  Iterator.register(zip_iterator)
  
  
  class Reversible(Iterable):
  
      __slots__ = ()
  
      @abstractmethod
      def __reversed__(self):
          while False:
              yield None
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Reversible:
              return _check_methods(C, "__reversed__", "__iter__")
          return NotImplemented
  
  
  class Generator(Iterator):
  
      __slots__ = ()
  
      def __next__(self):
          """Return the next item from the generator.
          When exhausted, raise StopIteration.
          """
          return self.send(None)
  
      @abstractmethod
      def send(self, value):
          """Send a value into the generator.
          Return next yielded value or raise StopIteration.
          """
          raise StopIteration
  
      @abstractmethod
      def throw(self, typ, val=None, tb=None):
          """Raise an exception in the generator.
          Return next yielded value or raise StopIteration.
          """
          if val is None:
              if tb is None:
                  raise typ
              val = typ()
          if tb is not None:
              val = val.with_traceback(tb)
          raise val
  
      def close(self):
          """Raise GeneratorExit inside generator.
          """
          try:
              self.throw(GeneratorExit)
          except (GeneratorExit, StopIteration):
              pass
          else:
              raise RuntimeError("generator ignored GeneratorExit")
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Generator:
              return _check_methods(C, '__iter__', '__next__',
                                    'send', 'throw', 'close')
          return NotImplemented
  
  
  Generator.register(generator)
  
  
  class Sized(metaclass=ABCMeta):
  
      __slots__ = ()
  
      @abstractmethod
      def __len__(self):
          return 0
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Sized:
              return _check_methods(C, "__len__")
          return NotImplemented
  
  
  class Container(metaclass=ABCMeta):
  
      __slots__ = ()
  
      @abstractmethod
      def __contains__(self, x):
          return False
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Container:
              return _check_methods(C, "__contains__")
          return NotImplemented
  
      __class_getitem__ = classmethod(GenericAlias)
  
  
  class Collection(Sized, Iterable, Container):
  
      __slots__ = ()
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Collection:
              return _check_methods(C,  "__len__", "__iter__", "__contains__")
          return NotImplemented
  
  
  class _CallableGenericAlias(GenericAlias):
      """ Represent `Callable[argtypes, resulttype]`.
  
      This sets ``__args__`` to a tuple containing the flattened ``argtypes``
      followed by ``resulttype``.
  
      Example: ``Callable[[int, str], float]`` sets ``__args__`` to
      ``(int, str, float)``.
      """
  
      __slots__ = ()
  
      def __new__(cls, origin, args):
          if not (isinstance(args, tuple) and len(args) == 2):
              raise TypeError(
                  "Callable must be used as Callable[[arg, ...], result].")
          t_args, t_result = args
          if isinstance(t_args, list):
              args = (*t_args, t_result)
          elif not _is_param_expr(t_args):
              raise TypeError(f"Expected a list of types, an ellipsis, "
                              f"ParamSpec, or Concatenate. Got {t_args}")
          return super().__new__(cls, origin, args)
  
      @property
      def __parameters__(self):
          params = []
          for arg in self.__args__:
              # Looks like a genericalias
              if hasattr(arg, "__parameters__") and isinstance(arg.__parameters__, tuple):
                  params.extend(arg.__parameters__)
              else:
                  if _is_typevarlike(arg):
                      params.append(arg)
          return tuple(dict.fromkeys(params))
  
      def __repr__(self):
          if len(self.__args__) == 2 and _is_param_expr(self.__args__[0]):
              return super().__repr__()
          return (f'collections.abc.Callable'
                  f'[[{", ".join([_type_repr(a) for a in self.__args__[:-1]])}], '
                  f'{_type_repr(self.__args__[-1])}]')
  
      def __reduce__(self):
          args = self.__args__
          if not (len(args) == 2 and _is_param_expr(args[0])):
              args = list(args[:-1]), args[-1]
          return _CallableGenericAlias, (Callable, args)
  
      def __getitem__(self, item):
          # Called during TypeVar substitution, returns the custom subclass
          # rather than the default types.GenericAlias object.  Most of the
          # code is copied from typing's _GenericAlias and the builtin
          # types.GenericAlias.
  
          # A special case in PEP 612 where if X = Callable[P, int],
          # then X[int, str] == X[[int, str]].
          param_len = len(self.__parameters__)
          if param_len == 0:
              raise TypeError(f'{self} is not a generic class')
          if not isinstance(item, tuple):
              item = (item,)
          if (param_len == 1 and _is_param_expr(self.__parameters__[0])
                  and item and not _is_param_expr(item[0])):
              item = (list(item),)
          item_len = len(item)
          if item_len != param_len:
              raise TypeError(f'Too {"many" if item_len > param_len else "few"}'
                              f' arguments for {self};'
                              f' actual {item_len}, expected {param_len}')
          subst = dict(zip(self.__parameters__, item))
          new_args = []
          for arg in self.__args__:
              if _is_typevarlike(arg):
                  if _is_param_expr(arg):
                      arg = subst[arg]
                      if not _is_param_expr(arg):
                          raise TypeError(f"Expected a list of types, an ellipsis, "
                                          f"ParamSpec, or Concatenate. Got {arg}")
                  else:
                      arg = subst[arg]
              # Looks like a GenericAlias
              elif hasattr(arg, '__parameters__') and isinstance(arg.__parameters__, tuple):
                  subparams = arg.__parameters__
                  if subparams:
                      subargs = tuple(subst[x] for x in subparams)
                      arg = arg[subargs]
              if isinstance(arg, tuple):
                  new_args.extend(arg)
              else:
                  new_args.append(arg)
  
          # args[0] occurs due to things like Z[[int, str, bool]] from PEP 612
          if not isinstance(new_args[0], list):
              t_result = new_args[-1]
              t_args = new_args[:-1]
              new_args = (t_args, t_result)
          return _CallableGenericAlias(Callable, tuple(new_args))
  
  
  def _is_typevarlike(arg):
      obj = type(arg)
      # looks like a TypeVar/ParamSpec
      return (obj.__module__ == 'typing'
              and obj.__name__ in {'ParamSpec', 'TypeVar'})
  
  def _is_param_expr(obj):
      """Checks if obj matches either a list of types, ``...``, ``ParamSpec`` or
      ``_ConcatenateGenericAlias`` from typing.py
      """
      if obj is Ellipsis:
          return True
      if isinstance(obj, list):
          return True
      obj = type(obj)
      names = ('ParamSpec', '_ConcatenateGenericAlias')
      return obj.__module__ == 'typing' and any(obj.__name__ == name for name in names)
  
  def _type_repr(obj):
      """Return the repr() of an object, special-casing types (internal helper).
  
      Copied from :mod:`typing` since collections.abc
      shouldn't depend on that module.
      """
      if isinstance(obj, GenericAlias):
          return repr(obj)
      if isinstance(obj, type):
          if obj.__module__ == 'builtins':
              return obj.__qualname__
          return f'{obj.__module__}.{obj.__qualname__}'
      if obj is Ellipsis:
          return '...'
      if isinstance(obj, FunctionType):
          return obj.__name__
      return repr(obj)
  
  
  class Callable(metaclass=ABCMeta):
  
      __slots__ = ()
  
      @abstractmethod
      def __call__(self, *args, **kwds):
          return False
  
      @classmethod
      def __subclasshook__(cls, C):
          if cls is Callable:
              return _check_methods(C, "__call__")
          return NotImplemented
  
      __class_getitem__ = classmethod(_CallableGenericAlias)
  
  
  ### SETS ###
  
  
  class Set(Collection):
      """A set is a finite, iterable container.
  
      This class provides concrete generic implementations of all
      methods except for __contains__, __iter__ and __len__.
  
      To override the comparisons (presumably for speed, as the
      semantics are fixed), redefine __le__ and __ge__,
      then the other operations will automatically follow suit.
      """
  
      __slots__ = ()
  
      def __le__(self, other):
          if not isinstance(other, Set):
              return NotImplemented
          if len(self) > len(other):
              return False
          for elem in self:
              if elem not in other:
                  return False
          return True
  
      def __lt__(self, other):
          if not isinstance(other, Set):
              return NotImplemented
          return len(self) < len(other) and self.__le__(other)
  
      def __gt__(self, other):
          if not isinstance(other, Set):
              return NotImplemented
          return len(self) > len(other) and self.__ge__(other)
  
      def __ge__(self, other):
          if not isinstance(other, Set):
              return NotImplemented
          if len(self) < len(other):
              return False
          for elem in other:
              if elem not in self:
                  return False
          return True
  
      def __eq__(self, other):
          if not isinstance(other, Set):
              return NotImplemented
          return len(self) == len(other) and self.__le__(other)
  
      @classmethod
      def _from_iterable(cls, it):
          '''Construct an instance of the class from any iterable input.
  
          Must override this method if the class constructor signature
          does not accept an iterable for an input.
          '''
          return cls(it)
  
      def __and__(self, other):
          if not isinstance(other, Iterable):
              return NotImplemented
          return self._from_iterable(value for value in other if value in self)
  
      __rand__ = __and__
  
      def isdisjoint(self, other):
          'Return True if two sets have a null intersection.'
          for value in other:
              if value in self:
                  return False
          return True
  
      def __or__(self, other):
          if not isinstance(other, Iterable):
              return NotImplemented
          chain = (e for s in (self, other) for e in s)
          return self._from_iterable(chain)
  
      __ror__ = __or__
  
      def __sub__(self, other):
          if not isinstance(other, Set):
              if not isinstance(other, Iterable):
                  return NotImplemented
              other = self._from_iterable(other)
          return self._from_iterable(value for value in self
                                     if value not in other)
  
      def __rsub__(self, other):
          if not isinstance(other, Set):
              if not isinstance(other, Iterable):
                  return NotImplemented
              other = self._from_iterable(other)
          return self._from_iterable(value for value in other
                                     if value not in self)
  
      def __xor__(self, other):
          if not isinstance(other, Set):
              if not isinstance(other, Iterable):
                  return NotImplemented
              other = self._from_iterable(other)
          return (self - other) | (other - self)
  
      __rxor__ = __xor__
  
      def _hash(self):
          """Compute the hash value of a set.
  
          Note that we don't define __hash__: not all sets are hashable.
          But if you define a hashable set type, its __hash__ should
          call this function.
  
          This must be compatible __eq__.
  
          All sets ought to compare equal if they contain the same
          elements, regardless of how they are implemented, and
          regardless of the order of the elements; so there's not much
          freedom for __eq__ or __hash__.  We match the algorithm used
          by the built-in frozenset type.
          """
          MAX = sys.maxsize
          MASK = 2 * MAX + 1
          n = len(self)
          h = 1927868237 * (n + 1)
          h &= MASK
          for x in self:
              hx = hash(x)
              h ^= (hx ^ (hx << 16) ^ 89869747)  * 3644798167
              h &= MASK
          h ^= (h >> 11) ^ (h >> 25)
          h = h * 69069 + 907133923
          h &= MASK
          if h > MAX:
              h -= MASK + 1
          if h == -1:
              h = 590923713
          return h
  
  
  Set.register(frozenset)
  
  
  class MutableSet(Set):
      """A mutable set is a finite, iterable container.
  
      This class provides concrete generic implementations of all
      methods except for __contains__, __iter__, __len__,
      add(), and discard().
  
      To override the comparisons (presumably for speed, as the
      semantics are fixed), all you have to do is redefine __le__ and
      then the other operations will automatically follow suit.
      """
  
      __slots__ = ()
  
      @abstractmethod
      def add(self, value):
          """Add an element."""
          raise NotImplementedError
  
      @abstractmethod
      def discard(self, value):
          """Remove an element.  Do not raise an exception if absent."""
          raise NotImplementedError
  
      def remove(self, value):
          """Remove an element. If not a member, raise a KeyError."""
          if value not in self:
              raise KeyError(value)
          self.discard(value)
  
      def pop(self):
          """Return the popped value.  Raise KeyError if empty."""
          it = iter(self)
          try:
              value = next(it)
          except StopIteration:
              raise KeyError from None
          self.discard(value)
          return value
  
      def clear(self):
          """This is slow (creates N new iterators!) but effective."""
          try:
              while True:
                  self.pop()
          except KeyError:
              pass
  
      def __ior__(self, it):
          for value in it:
              self.add(value)
          return self
  
      def __iand__(self, it):
          for value in (self - it):
              self.discard(value)
          return self
  
      def __ixor__(self, it):
          if it is self:
              self.clear()
          else:
              if not isinstance(it, Set):
                  it = self._from_iterable(it)
              for value in it:
                  if value in self:
                      self.discard(value)
                  else:
                      self.add(value)
          return self
  
      def __isub__(self, it):
          if it is self:
              self.clear()
          else:
              for value in it:
                  self.discard(value)
          return self
  
  
  MutableSet.register(set)
  
  
  ### MAPPINGS ###
  
  class Mapping(Collection):
      """A Mapping is a generic container for associating key/value
      pairs.
  
      This class provides concrete generic implementations of all
      methods except for __getitem__, __iter__, and __len__.
      """
  
      __slots__ = ()
  
      # Tell ABCMeta.__new__ that this class should have TPFLAGS_MAPPING set.
      __abc_tpflags__ = 1 << 6 # Py_TPFLAGS_MAPPING
  
      @abstractmethod
      def __getitem__(self, key):
          raise KeyError
  
      def get(self, key, default=None):
          'D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None.'
          try:
              return self[key]
          except KeyError:
              return default
  
      def __contains__(self, key):
          try:
              self[key]
          except KeyError:
              return False
          else:
              return True
  
      def keys(self):
          "D.keys() -> a set-like object providing a view on D's keys"
          return KeysView(self)
  
      def items(self):
          "D.items() -> a set-like object providing a view on D's items"
          return ItemsView(self)
  
      def values(self):
          "D.values() -> an object providing a view on D's values"
          return ValuesView(self)
  
      def __eq__(self, other):
          if not isinstance(other, Mapping):
              return NotImplemented
          return dict(self.items()) == dict(other.items())
  
      __reversed__ = None
  
  Mapping.register(mappingproxy)
  
  
  class MappingView(Sized):
  
      __slots__ = '_mapping',
  
      def __init__(self, mapping):
          self._mapping = mapping
  
      def __len__(self):
          return len(self._mapping)
  
      def __repr__(self):
          return '{0.__class__.__name__}({0._mapping!r})'.format(self)
  
      __class_getitem__ = classmethod(GenericAlias)
  
  
  class KeysView(MappingView, Set):
  
      __slots__ = ()
  
      @classmethod
      def _from_iterable(cls, it):
          return set(it)
  
      def __contains__(self, key):
          return key in self._mapping
  
      def __iter__(self):
          yield from self._mapping
  
  
  KeysView.register(dict_keys)
  
  
  class ItemsView(MappingView, Set):
  
      __slots__ = ()
  
      @classmethod
      def _from_iterable(cls, it):
          return set(it)
  
      def __contains__(self, item):
          key, value = item
          try:
              v = self._mapping[key]
          except KeyError:
              return False
          else:
              return v is value or v == value
  
      def __iter__(self):
          for key in self._mapping:
              yield (key, self._mapping[key])
  
  
  ItemsView.register(dict_items)
  
  
  class ValuesView(MappingView, Collection):
  
      __slots__ = ()
  
      def __contains__(self, value):
          for key in self._mapping:
              v = self._mapping[key]
              if v is value or v == value:
                  return True
          return False
  
      def __iter__(self):
          for key in self._mapping:
              yield self._mapping[key]
  
  
  ValuesView.register(dict_values)
  
  
  class MutableMapping(Mapping):
      """A MutableMapping is a generic container for associating
      key/value pairs.
  
      This class provides concrete generic implementations of all
      methods except for __getitem__, __setitem__, __delitem__,
      __iter__, and __len__.
      """
  
      __slots__ = ()
  
      @abstractmethod
      def __setitem__(self, key, value):
          raise KeyError
  
      @abstractmethod
      def __delitem__(self, key):
          raise KeyError
  
      __marker = object()
  
      def pop(self, key, default=__marker):
          '''D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
            If key is not found, d is returned if given, otherwise KeyError is raised.
          '''
          try:
              value = self[key]
          except KeyError:
              if default is self.__marker:
                  raise
              return default
          else:
              del self[key]
              return value
  
      def popitem(self):
          '''D.popitem() -> (k, v), remove and return some (key, value) pair
             as a 2-tuple; but raise KeyError if D is empty.
          '''
          try:
              key = next(iter(self))
          except StopIteration:
              raise KeyError from None
          value = self[key]
          del self[key]
          return key, value
  
      def clear(self):
          'D.clear() -> None.  Remove all items from D.'
          try:
              while True:
                  self.popitem()
          except KeyError:
              pass
  
      def update(self, other=(), /, **kwds):
          ''' D.update([E, ]**F) -> None.  Update D from mapping/iterable E and F.
              If E present and has a .keys() method, does:     for k in E: D[k] = E[k]
              If E present and lacks .keys() method, does:     for (k, v) in E: D[k] = v
              In either case, this is followed by: for k, v in F.items(): D[k] = v
          '''
          if isinstance(other, Mapping):
              for key in other:
                  self[key] = other[key]
          elif hasattr(other, "keys"):
              for key in other.keys():
                  self[key] = other[key]
          else:
              for key, value in other:
                  self[key] = value
          for key, value in kwds.items():
              self[key] = value
  
      def setdefault(self, key, default=None):
          'D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D'
          try:
              return self[key]
          except KeyError:
              self[key] = default
          return default
  
  
  MutableMapping.register(dict)
  
  
  ### SEQUENCES ###
  
  class Sequence(Reversible, Collection):
      """All the operations on a read-only sequence.
  
      Concrete subclasses must override __new__ or __init__,
      __getitem__, and __len__.
      """
  
      __slots__ = ()
  
      # Tell ABCMeta.__new__ that this class should have TPFLAGS_SEQUENCE set.
      __abc_tpflags__ = 1 << 5 # Py_TPFLAGS_SEQUENCE
  
      @abstractmethod
      def __getitem__(self, index):
          raise IndexError
  
      def __iter__(self):
          i = 0
          try:
              while True:
                  v = self[i]
                  yield v
                  i += 1
          except IndexError:
              return
  
      def __contains__(self, value):
          for v in self:
              if v is value or v == value:
                  return True
          return False
  
      def __reversed__(self):
          for i in reversed(range(len(self))):
              yield self[i]
  
      def index(self, value, start=0, stop=None):
          '''S.index(value, [start, [stop]]) -> integer -- return first index of value.
             Raises ValueError if the value is not present.
  
             Supporting start and stop arguments is optional, but
             recommended.
          '''
          if start is not None and start < 0:
              start = max(len(self) + start, 0)
          if stop is not None and stop < 0:
              stop += len(self)
  
          i = start
          while stop is None or i < stop:
              try:
                  v = self[i]
                  if v is value or v == value:
                      return i
              except IndexError:
                  break
              i += 1
          raise ValueError
  
      def count(self, value):
          'S.count(value) -> integer -- return number of occurrences of value'
          return sum(1 for v in self if v is value or v == value)
  
  Sequence.register(tuple)
  Sequence.register(str)
  Sequence.register(range)
  Sequence.register(memoryview)
  
  
  class ByteString(Sequence):
      """This unifies bytes and bytearray.
  
      XXX Should add all their methods.
      """
  
      __slots__ = ()
  
  ByteString.register(bytes)
  ByteString.register(bytearray)
  
  
  class MutableSequence(Sequence):
      """All the operations on a read-write sequence.
  
      Concrete subclasses must provide __new__ or __init__,
      __getitem__, __setitem__, __delitem__, __len__, and insert().
      """
  
      __slots__ = ()
  
      @abstractmethod
      def __setitem__(self, index, value):
          raise IndexError
  
      @abstractmethod
      def __delitem__(self, index):
          raise IndexError
  
      @abstractmethod
      def insert(self, index, value):
          'S.insert(index, value) -- insert value before index'
          raise IndexError
  
      def append(self, value):
          'S.append(value) -- append value to the end of the sequence'
          self.insert(len(self), value)
  
      def clear(self):
          'S.clear() -> None -- remove all items from S'
          try:
              while True:
                  self.pop()
          except IndexError:
              pass
  
      def reverse(self):
          'S.reverse() -- reverse *IN PLACE*'
          n = len(self)
          for i in range(n//2):
              self[i], self[n-i-1] = self[n-i-1], self[i]
  
      def extend(self, values):
          'S.extend(iterable) -- extend sequence by appending elements from the iterable'
          if values is self:
              values = list(values)
          for v in values:
              self.append(v)
  
      def pop(self, index=-1):
          '''S.pop([index]) -> item -- remove and return item at index (default last).
             Raise IndexError if list is empty or index is out of range.
          '''
          v = self[index]
          del self[index]
          return v
  
      def remove(self, value):
          '''S.remove(value) -- remove first occurrence of value.
             Raise ValueError if the value is not present.
          '''
          del self[self.index(value)]
  
      def __iadd__(self, values):
          self.extend(values)
          return self
  
  
  MutableSequence.register(list)
  MutableSequence.register(bytearray)  # Multiply inheriting, see ByteString
  