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diff --git a/Lib/collections/abc.py b/Lib/collections/abc.py
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+# 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
+
+__all__ = ["Hashable", "Iterable", "Iterator",
+           "Sized", "Container", "Callable",
+           "Set", "MutableSet",
+           "Mapping", "MutableMapping",
+           "MappingView", "KeysView", "ItemsView", "ValuesView",
+           "Sequence", "MutableSequence",
+           "ByteString",
+           ]
+
+
+### collection related types which are not exposed through builtin ###
+## iterators ##
+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)))
+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 ##
+dict_proxy = type(type.__dict__)
+
+
+### ONE-TRICK PONIES ###
+
+class Hashable(metaclass=ABCMeta):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __hash__(self):
+        return 0
+
+    @classmethod
+    def __subclasshook__(cls, C):
+        if cls is Hashable:
+            for B in C.__mro__:
+                if "__hash__" in B.__dict__:
+                    if B.__dict__["__hash__"]:
+                        return True
+                    break
+        return NotImplemented
+
+
+class Iterable(metaclass=ABCMeta):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __iter__(self):
+        while False:
+            yield None
+
+    @classmethod
+    def __subclasshook__(cls, C):
+        if cls is Iterable:
+            if any("__iter__" in B.__dict__ for B in C.__mro__):
+                return True
+        return NotImplemented
+
+
+class Iterator(Iterable):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __next__(self):
+        raise StopIteration
+
+    def __iter__(self):
+        return self
+
+    @classmethod
+    def __subclasshook__(cls, C):
+        if cls is Iterator:
+            if (any("__next__" in B.__dict__ for B in C.__mro__) and
+                any("__iter__" in B.__dict__ for B in C.__mro__)):
+                return True
+        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(set_iterator)
+Iterator.register(str_iterator)
+Iterator.register(tuple_iterator)
+Iterator.register(zip_iterator)
+
+class Sized(metaclass=ABCMeta):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __len__(self):
+        return 0
+
+    @classmethod
+    def __subclasshook__(cls, C):
+        if cls is Sized:
+            if any("__len__" in B.__dict__ for B in C.__mro__):
+                return True
+        return NotImplemented
+
+
+class Container(metaclass=ABCMeta):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __contains__(self, x):
+        return False
+
+    @classmethod
+    def __subclasshook__(cls, C):
+        if cls is Container:
+            if any("__contains__" in B.__dict__ for B in C.__mro__):
+                return True
+        return NotImplemented
+
+
+class Callable(metaclass=ABCMeta):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __call__(self, *args, **kwds):
+        return False
+
+    @classmethod
+    def __subclasshook__(cls, C):
+        if cls is Callable:
+            if any("__call__" in B.__dict__ for B in C.__mro__):
+                return True
+        return NotImplemented
+
+
+### SETS ###
+
+
+class Set(Sized, Iterable, Container):
+
+    """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), all you have to do is redefine __le__ and
+    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 other < self
+
+    def __ge__(self, other):
+        if not isinstance(other, Set):
+            return NotImplemented
+        return other <= self
+
+    def __eq__(self, other):
+        if not isinstance(other, Set):
+            return NotImplemented
+        return len(self) == len(other) and self.__le__(other)
+
+    def __ne__(self, other):
+        return not (self == 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)
+
+    def isdisjoint(self, other):
+        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)
+
+    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 __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)
+
+    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 * 69069 + 907133923
+        h &= MASK
+        if h > MAX:
+            h -= MASK + 1
+        if h == -1:
+            h = 590923713
+        return h
+
+Set.register(frozenset)
+
+
+class MutableSet(Set):
+
+    __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
+        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(Sized, Iterable, Container):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __getitem__(self, key):
+        raise KeyError
+
+    def get(self, key, default=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):
+        return KeysView(self)
+
+    def items(self):
+        return ItemsView(self)
+
+    def values(self):
+        return ValuesView(self)
+
+    def __eq__(self, other):
+        if not isinstance(other, Mapping):
+            return NotImplemented
+        return dict(self.items()) == dict(other.items())
+
+    def __ne__(self, other):
+        return not (self == other)
+
+
+class MappingView(Sized):
+
+    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 KeysView(MappingView, Set):
+
+    @classmethod
+    def _from_iterable(self, it):
+        return set(it)
+
+    def __contains__(self, key):
+        return key in self._mapping
+
+    def __iter__(self):
+        for key in self._mapping:
+            yield key
+
+KeysView.register(dict_keys)
+
+
+class ItemsView(MappingView, Set):
+
+    @classmethod
+    def _from_iterable(self, it):
+        return set(it)
+
+    def __contains__(self, item):
+        key, value = item
+        try:
+            v = self._mapping[key]
+        except KeyError:
+            return False
+        else:
+            return v == value
+
+    def __iter__(self):
+        for key in self._mapping:
+            yield (key, self._mapping[key])
+
+ItemsView.register(dict_items)
+
+
+class ValuesView(MappingView):
+
+    def __contains__(self, value):
+        for key in self._mapping:
+            if value == self._mapping[key]:
+                return True
+        return False
+
+    def __iter__(self):
+        for key in self._mapping:
+            yield self._mapping[key]
+
+ValuesView.register(dict_values)
+
+
+class MutableMapping(Mapping):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __setitem__(self, key, value):
+        raise KeyError
+
+    @abstractmethod
+    def __delitem__(self, key):
+        raise KeyError
+
+    __marker = object()
+
+    def pop(self, key, default=__marker):
+        try:
+            value = self[key]
+        except KeyError:
+            if default is self.__marker:
+                raise
+            return default
+        else:
+            del self[key]
+            return value
+
+    def popitem(self):
+        try:
+            key = next(iter(self))
+        except StopIteration:
+            raise KeyError
+        value = self[key]
+        del self[key]
+        return key, value
+
+    def clear(self):
+        try:
+            while True:
+                self.popitem()
+        except KeyError:
+            pass
+
+    def update(*args, **kwds):
+        if len(args) > 2:
+            raise TypeError("update() takes at most 2 positional "
+                            "arguments ({} given)".format(len(args)))
+        elif not args:
+            raise TypeError("update() takes at least 1 argument (0 given)")
+        self = args[0]
+        other = args[1] if len(args) >= 2 else ()
+
+        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):
+        try:
+            return self[key]
+        except KeyError:
+            self[key] = default
+        return default
+
+MutableMapping.register(dict)
+
+
+### SEQUENCES ###
+
+
+class Sequence(Sized, Iterable, Container):
+
+    """All the operations on a read-only sequence.
+
+    Concrete subclasses must override __new__ or __init__,
+    __getitem__, and __len__.
+    """
+
+    __slots__ = ()
+
+    @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 == value:
+                return True
+        return False
+
+    def __reversed__(self):
+        for i in reversed(range(len(self))):
+            yield self[i]
+
+    def index(self, value):
+        for i, v in enumerate(self):
+            if v == value:
+                return i
+        raise ValueError
+
+    def count(self, value):
+        return sum(1 for v in self if v == value)
+
+Sequence.register(tuple)
+Sequence.register(str)
+Sequence.register(range)
+
+
+class ByteString(Sequence):
+
+    """This unifies bytes and bytearray.
+
+    XXX Should add all their methods.
+    """
+
+    __slots__ = ()
+
+ByteString.register(bytes)
+ByteString.register(bytearray)
+
+
+class MutableSequence(Sequence):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __setitem__(self, index, value):
+        raise IndexError
+
+    @abstractmethod
+    def __delitem__(self, index):
+        raise IndexError
+
+    @abstractmethod
+    def insert(self, index, value):
+        raise IndexError
+
+    def append(self, value):
+        self.insert(len(self), value)
+
+    def clear(self):
+        try:
+            while True:
+                self.pop()
+        except IndexError:
+            pass
+
+    def reverse(self):
+        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):
+        for v in values:
+            self.append(v)
+
+    def pop(self, index=-1):
+        v = self[index]
+        del self[index]
+        return v
+
+    def remove(self, value):
+        del self[self.index(value)]
+
+    def __iadd__(self, values):
+        self.extend(values)
+        return self
+
+MutableSequence.register(list)
+MutableSequence.register(bytearray)  # Multiply inheriting, see ByteString