#11515: Merge with 3.2.

1 files changed, 1046 insertions, 0 deletions

diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
new file mode 100644
index 0000000000..c324ce3bd6
--- /dev/null
+++ b/Lib/collections/__init__.py
@@ -0,0 +1,1046 @@
+__all__ = ['deque', 'defaultdict', 'namedtuple', 'UserDict', 'UserList',
+            'UserString', 'Counter', 'OrderedDict']
+
+# For backwards compatibility, continue to make the collections ABCs
+# available through the collections module.
+from collections.abc import *
+import collections.abc
+__all__ += collections.abc.__all__
+
+from _collections import deque, defaultdict
+from operator import itemgetter as _itemgetter
+from keyword import iskeyword as _iskeyword
+import sys as _sys
+import heapq as _heapq
+from weakref import proxy as _proxy
+from itertools import repeat as _repeat, chain as _chain, starmap as _starmap
+from reprlib import recursive_repr as _recursive_repr
+
+################################################################################
+### OrderedDict
+################################################################################
+
+class _Link(object):
+    __slots__ = 'prev', 'next', 'key', '__weakref__'
+
+class OrderedDict(dict):
+    'Dictionary that remembers insertion order'
+    # An inherited dict maps keys to values.
+    # The inherited dict provides __getitem__, __len__, __contains__, and get.
+    # The remaining methods are order-aware.
+    # Big-O running times for all methods are the same as for regular dictionaries.
+
+    # The internal self.__map dictionary maps keys to links in a doubly linked list.
+    # The circular doubly linked list starts and ends with a sentinel element.
+    # The sentinel element never gets deleted (this simplifies the algorithm).
+    # The sentinel is stored in self.__hardroot with a weakref proxy in self.__root.
+    # The prev/next links are weakref proxies (to prevent circular references).
+    # Individual links are kept alive by the hard reference in self.__map.
+    # Those hard references disappear when a key is deleted from an OrderedDict.
+
+    def __init__(self, *args, **kwds):
+        '''Initialize an ordered dictionary.  Signature is the same as for
+        regular dictionaries, but keyword arguments are not recommended
+        because their insertion order is arbitrary.
+
+        '''
+        if len(args) > 1:
+            raise TypeError('expected at most 1 arguments, got %d' % len(args))
+        try:
+            self.__root
+        except AttributeError:
+            self.__hardroot = _Link()
+            self.__root = root = _proxy(self.__hardroot)
+            root.prev = root.next = root
+            self.__map = {}
+        self.__update(*args, **kwds)
+
+    def __setitem__(self, key, value,
+                    dict_setitem=dict.__setitem__, proxy=_proxy, Link=_Link):
+        'od.__setitem__(i, y) <==> od[i]=y'
+        # Setting a new item creates a new link which goes at the end of the linked
+        # list, and the inherited dictionary is updated with the new key/value pair.
+        if key not in self:
+            self.__map[key] = link = Link()
+            root = self.__root
+            last = root.prev
+            link.prev, link.next, link.key = last, root, key
+            last.next = link
+            root.prev = proxy(link)
+        dict_setitem(self, key, value)
+
+    def __delitem__(self, key, dict_delitem=dict.__delitem__):
+        'od.__delitem__(y) <==> del od[y]'
+        # Deleting an existing item uses self.__map to find the link which is
+        # then removed by updating the links in the predecessor and successor nodes.
+        dict_delitem(self, key)
+        link = self.__map.pop(key)
+        link_prev = link.prev
+        link_next = link.next
+        link_prev.next = link_next
+        link_next.prev = link_prev
+
+    def __iter__(self):
+        'od.__iter__() <==> iter(od)'
+        # Traverse the linked list in order.
+        root = self.__root
+        curr = root.next
+        while curr is not root:
+            yield curr.key
+            curr = curr.next
+
+    def __reversed__(self):
+        'od.__reversed__() <==> reversed(od)'
+        # Traverse the linked list in reverse order.
+        root = self.__root
+        curr = root.prev
+        while curr is not root:
+            yield curr.key
+            curr = curr.prev
+
+    def clear(self):
+        'od.clear() -> None.  Remove all items from od.'
+        root = self.__root
+        root.prev = root.next = root
+        self.__map.clear()
+        dict.clear(self)
+
+    def popitem(self, last=True):
+        '''od.popitem() -> (k, v), return and remove a (key, value) pair.
+        Pairs are returned in LIFO order if last is true or FIFO order if false.
+
+        '''
+        if not self:
+            raise KeyError('dictionary is empty')
+        root = self.__root
+        if last:
+            link = root.prev
+            link_prev = link.prev
+            link_prev.next = root
+            root.prev = link_prev
+        else:
+            link = root.next
+            link_next = link.next
+            root.next = link_next
+            link_next.prev = root
+        key = link.key
+        del self.__map[key]
+        value = dict.pop(self, key)
+        return key, value
+
+    def move_to_end(self, key, last=True):
+        '''Move an existing element to the end (or beginning if last==False).
+
+        Raises KeyError if the element does not exist.
+        When last=True, acts like a fast version of self[key]=self.pop(key).
+
+        '''
+        link = self.__map[key]
+        link_prev = link.prev
+        link_next = link.next
+        link_prev.next = link_next
+        link_next.prev = link_prev
+        root = self.__root
+        if last:
+            last = root.prev
+            link.prev = last
+            link.next = root
+            last.next = root.prev = link
+        else:
+            first = root.next
+            link.prev = root
+            link.next = first
+            root.next = first.prev = link
+
+    def __reduce__(self):
+        'Return state information for pickling'
+        items = [[k, self[k]] for k in self]
+        tmp = self.__map, self.__root, self.__hardroot
+        del self.__map, self.__root, self.__hardroot
+        inst_dict = vars(self).copy()
+        self.__map, self.__root, self.__hardroot = tmp
+        if inst_dict:
+            return (self.__class__, (items,), inst_dict)
+        return self.__class__, (items,)
+
+    def __sizeof__(self):
+        sizeof = _sys.getsizeof
+        n = len(self) + 1                       # number of links including root
+        size = sizeof(self.__dict__)            # instance dictionary
+        size += sizeof(self.__map) * 2          # internal dict and inherited dict
+        size += sizeof(self.__hardroot) * n     # link objects
+        size += sizeof(self.__root) * n         # proxy objects
+        return size
+
+    update = __update = MutableMapping.update
+    keys = MutableMapping.keys
+    values = MutableMapping.values
+    items = MutableMapping.items
+    __ne__ = MutableMapping.__ne__
+
+    __marker = object()
+
+    def pop(self, key, default=__marker):
+        if key in self:
+            result = self[key]
+            del self[key]
+            return result
+        if default is self.__marker:
+            raise KeyError(key)
+        return default
+
+    def setdefault(self, key, default=None):
+        'OD.setdefault(k[,d]) -> OD.get(k,d), also set OD[k]=d if k not in OD'
+        if key in self:
+            return self[key]
+        self[key] = default
+        return default
+
+    @_recursive_repr()
+    def __repr__(self):
+        'od.__repr__() <==> repr(od)'
+        if not self:
+            return '%s()' % (self.__class__.__name__,)
+        return '%s(%r)' % (self.__class__.__name__, list(self.items()))
+
+    def copy(self):
+        'od.copy() -> a shallow copy of od'
+        return self.__class__(self)
+
+    @classmethod
+    def fromkeys(cls, iterable, value=None):
+        '''OD.fromkeys(S[, v]) -> New ordered dictionary with keys from S
+        and values equal to v (which defaults to None).
+
+        '''
+        d = cls()
+        for key in iterable:
+            d[key] = value
+        return d
+
+    def __eq__(self, other):
+        '''od.__eq__(y) <==> od==y.  Comparison to another OD is order-sensitive
+        while comparison to a regular mapping is order-insensitive.
+
+        '''
+        if isinstance(other, OrderedDict):
+            return len(self)==len(other) and \
+                   all(p==q for p, q in zip(self.items(), other.items()))
+        return dict.__eq__(self, other)
+
+
+################################################################################
+### namedtuple
+################################################################################
+
+def namedtuple(typename, field_names, verbose=False, rename=False):
+    """Returns a new subclass of tuple with named fields.
+
+    >>> Point = namedtuple('Point', 'x y')
+    >>> Point.__doc__                   # docstring for the new class
+    'Point(x, y)'
+    >>> p = Point(11, y=22)             # instantiate with positional args or keywords
+    >>> p[0] + p[1]                     # indexable like a plain tuple
+    33
+    >>> x, y = p                        # unpack like a regular tuple
+    >>> x, y
+    (11, 22)
+    >>> p.x + p.y                       # fields also accessable by name
+    33
+    >>> d = p._asdict()                 # convert to a dictionary
+    >>> d['x']
+    11
+    >>> Point(**d)                      # convert from a dictionary
+    Point(x=11, y=22)
+    >>> p._replace(x=100)               # _replace() is like str.replace() but targets named fields
+    Point(x=100, y=22)
+
+    """
+
+    # Parse and validate the field names.  Validation serves two purposes,
+    # generating informative error messages and preventing template injection attacks.
+    if isinstance(field_names, str):
+        field_names = field_names.replace(',', ' ').split() # names separated by whitespace and/or commas
+    field_names = tuple(map(str, field_names))
+    if rename:
+        names = list(field_names)
+        seen = set()
+        for i, name in enumerate(names):
+            if (not all(c.isalnum() or c=='_' for c in name) or _iskeyword(name)
+                or not name or name[0].isdigit() or name.startswith('_')
+                or name in seen):
+                names[i] = '_%d' % i
+            seen.add(name)
+        field_names = tuple(names)
+    for name in (typename,) + field_names:
+        if not all(c.isalnum() or c=='_' for c in name):
+            raise ValueError('Type names and field names can only contain alphanumeric characters and underscores: %r' % name)
+        if _iskeyword(name):
+            raise ValueError('Type names and field names cannot be a keyword: %r' % name)
+        if name[0].isdigit():
+            raise ValueError('Type names and field names cannot start with a number: %r' % name)
+    seen_names = set()
+    for name in field_names:
+        if name.startswith('_') and not rename:
+            raise ValueError('Field names cannot start with an underscore: %r' % name)
+        if name in seen_names:
+            raise ValueError('Encountered duplicate field name: %r' % name)
+        seen_names.add(name)
+
+    # Create and fill-in the class template
+    numfields = len(field_names)
+    argtxt = repr(field_names).replace("'", "")[1:-1]   # tuple repr without parens or quotes
+    reprtxt = ', '.join('%s=%%r' % name for name in field_names)
+    template = '''class %(typename)s(tuple):
+        '%(typename)s(%(argtxt)s)' \n
+        __slots__ = () \n
+        _fields = %(field_names)r \n
+        def __new__(_cls, %(argtxt)s):
+            'Create new instance of %(typename)s(%(argtxt)s)'
+            return _tuple.__new__(_cls, (%(argtxt)s)) \n
+        @classmethod
+        def _make(cls, iterable, new=tuple.__new__, len=len):
+            'Make a new %(typename)s object from a sequence or iterable'
+            result = new(cls, iterable)
+            if len(result) != %(numfields)d:
+                raise TypeError('Expected %(numfields)d arguments, got %%d' %% len(result))
+            return result \n
+        def __repr__(self):
+            'Return a nicely formatted representation string'
+            return self.__class__.__name__ + '(%(reprtxt)s)' %% self \n
+        def _asdict(self):
+            'Return a new OrderedDict which maps field names to their values'
+            return OrderedDict(zip(self._fields, self)) \n
+        def _replace(_self, **kwds):
+            'Return a new %(typename)s object replacing specified fields with new values'
+            result = _self._make(map(kwds.pop, %(field_names)r, _self))
+            if kwds:
+                raise ValueError('Got unexpected field names: %%r' %% kwds.keys())
+            return result \n
+        def __getnewargs__(self):
+            'Return self as a plain tuple.  Used by copy and pickle.'
+            return tuple(self) \n\n''' % locals()
+    for i, name in enumerate(field_names):
+        template += "        %s = _property(_itemgetter(%d), doc='Alias for field number %d')\n" % (name, i, i)
+    if verbose:
+        print(template)
+
+    # Execute the template string in a temporary namespace and
+    # support tracing utilities by setting a value for frame.f_globals['__name__']
+    namespace = dict(_itemgetter=_itemgetter, __name__='namedtuple_%s' % typename,
+                     OrderedDict=OrderedDict, _property=property, _tuple=tuple)
+    try:
+        exec(template, namespace)
+    except SyntaxError as e:
+        raise SyntaxError(e.msg + ':\n\n' + template)
+    result = namespace[typename]
+
+    # For pickling to work, the __module__ variable needs to be set to the frame
+    # where the named tuple is created.  Bypass this step in enviroments where
+    # sys._getframe is not defined (Jython for example) or sys._getframe is not
+    # defined for arguments greater than 0 (IronPython).
+    try:
+        result.__module__ = _sys._getframe(1).f_globals.get('__name__', '__main__')
+    except (AttributeError, ValueError):
+        pass
+
+    return result
+
+
+########################################################################
+###  Counter
+########################################################################
+
+def _count_elements(mapping, iterable):
+    'Tally elements from the iterable.'
+    mapping_get = mapping.get
+    for elem in iterable:
+        mapping[elem] = mapping_get(elem, 0) + 1
+
+try:                                    # Load C helper function if available
+    from _collections import _count_elements
+except ImportError:
+    pass
+
+class Counter(dict):
+    '''Dict subclass for counting hashable items.  Sometimes called a bag
+    or multiset.  Elements are stored as dictionary keys and their counts
+    are stored as dictionary values.
+
+    >>> c = Counter('abcdeabcdabcaba')  # count elements from a string
+
+    >>> c.most_common(3)                # three most common elements
+    [('a', 5), ('b', 4), ('c', 3)]
+    >>> sorted(c)                       # list all unique elements
+    ['a', 'b', 'c', 'd', 'e']
+    >>> ''.join(sorted(c.elements()))   # list elements with repetitions
+    'aaaaabbbbcccdde'
+    >>> sum(c.values())                 # total of all counts
+    15
+
+    >>> c['a']                          # count of letter 'a'
+    5
+    >>> for elem in 'shazam':           # update counts from an iterable
+    ...     c[elem] += 1                # by adding 1 to each element's count
+    >>> c['a']                          # now there are seven 'a'
+    7
+    >>> del c['b']                      # remove all 'b'
+    >>> c['b']                          # now there are zero 'b'
+    0
+
+    >>> d = Counter('simsalabim')       # make another counter
+    >>> c.update(d)                     # add in the second counter
+    >>> c['a']                          # now there are nine 'a'
+    9
+
+    >>> c.clear()                       # empty the counter
+    >>> c
+    Counter()
+
+    Note:  If a count is set to zero or reduced to zero, it will remain
+    in the counter until the entry is deleted or the counter is cleared:
+
+    >>> c = Counter('aaabbc')
+    >>> c['b'] -= 2                     # reduce the count of 'b' by two
+    >>> c.most_common()                 # 'b' is still in, but its count is zero
+    [('a', 3), ('c', 1), ('b', 0)]
+
+    '''
+    # References:
+    #   http://en.wikipedia.org/wiki/Multiset
+    #   http://www.gnu.org/software/smalltalk/manual-base/html_node/Bag.html
+    #   http://www.demo2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm
+    #   http://code.activestate.com/recipes/259174/
+    #   Knuth, TAOCP Vol. II section 4.6.3
+
+    def __init__(self, iterable=None, **kwds):
+        '''Create a new, empty Counter object.  And if given, count elements
+        from an input iterable.  Or, initialize the count from another mapping
+        of elements to their counts.
+
+        >>> c = Counter()                           # a new, empty counter
+        >>> c = Counter('gallahad')                 # a new counter from an iterable
+        >>> c = Counter({'a': 4, 'b': 2})           # a new counter from a mapping
+        >>> c = Counter(a=4, b=2)                   # a new counter from keyword args
+
+        '''
+        super().__init__()
+        self.update(iterable, **kwds)
+
+    def __missing__(self, key):
+        'The count of elements not in the Counter is zero.'
+        # Needed so that self[missing_item] does not raise KeyError
+        return 0
+
+    def most_common(self, n=None):
+        '''List the n most common elements and their counts from the most
+        common to the least.  If n is None, then list all element counts.
+
+        >>> Counter('abcdeabcdabcaba').most_common(3)
+        [('a', 5), ('b', 4), ('c', 3)]
+
+        '''
+        # Emulate Bag.sortedByCount from Smalltalk
+        if n is None:
+            return sorted(self.items(), key=_itemgetter(1), reverse=True)
+        return _heapq.nlargest(n, self.items(), key=_itemgetter(1))
+
+    def elements(self):
+        '''Iterator over elements repeating each as many times as its count.
+
+        >>> c = Counter('ABCABC')
+        >>> sorted(c.elements())
+        ['A', 'A', 'B', 'B', 'C', 'C']
+
+        # Knuth's example for prime factors of 1836:  2**2 * 3**3 * 17**1
+        >>> prime_factors = Counter({2: 2, 3: 3, 17: 1})
+        >>> product = 1
+        >>> for factor in prime_factors.elements():     # loop over factors
+        ...     product *= factor                       # and multiply them
+        >>> product
+        1836
+
+        Note, if an element's count has been set to zero or is a negative
+        number, elements() will ignore it.
+
+        '''
+        # Emulate Bag.do from Smalltalk and Multiset.begin from C++.
+        return _chain.from_iterable(_starmap(_repeat, self.items()))
+
+    # Override dict methods where necessary
+
+    @classmethod
+    def fromkeys(cls, iterable, v=None):
+        # There is no equivalent method for counters because setting v=1
+        # means that no element can have a count greater than one.
+        raise NotImplementedError(
+            'Counter.fromkeys() is undefined.  Use Counter(iterable) instead.')
+
+    def update(self, iterable=None, **kwds):
+        '''Like dict.update() but add counts instead of replacing them.
+
+        Source can be an iterable, a dictionary, or another Counter instance.
+
+        >>> c = Counter('which')
+        >>> c.update('witch')           # add elements from another iterable
+        >>> d = Counter('watch')
+        >>> c.update(d)                 # add elements from another counter
+        >>> c['h']                      # four 'h' in which, witch, and watch
+        4
+
+        '''
+        # The regular dict.update() operation makes no sense here because the
+        # replace behavior results in the some of original untouched counts
+        # being mixed-in with all of the other counts for a mismash that
+        # doesn't have a straight-forward interpretation in most counting
+        # contexts.  Instead, we implement straight-addition.  Both the inputs
+        # and outputs are allowed to contain zero and negative counts.
+
+        if iterable is not None:
+            if isinstance(iterable, Mapping):
+                if self:
+                    self_get = self.get
+                    for elem, count in iterable.items():
+                        self[elem] = count + self_get(elem, 0)
+                else:
+                    super().update(iterable) # fast path when counter is empty
+            else:
+                _count_elements(self, iterable)
+        if kwds:
+            self.update(kwds)
+
+    def subtract(self, iterable=None, **kwds):
+        '''Like dict.update() but subtracts counts instead of replacing them.
+        Counts can be reduced below zero.  Both the inputs and outputs are
+        allowed to contain zero and negative counts.
+
+        Source can be an iterable, a dictionary, or another Counter instance.
+
+        >>> c = Counter('which')
+        >>> c.subtract('witch')             # subtract elements from another iterable
+        >>> c.subtract(Counter('watch'))    # subtract elements from another counter
+        >>> c['h']                          # 2 in which, minus 1 in witch, minus 1 in watch
+        0
+        >>> c['w']                          # 1 in which, minus 1 in witch, minus 1 in watch
+        -1
+
+        '''
+        if iterable is not None:
+            self_get = self.get
+            if isinstance(iterable, Mapping):
+                for elem, count in iterable.items():
+                    self[elem] = self_get(elem, 0) - count
+            else:
+                for elem in iterable:
+                    self[elem] = self_get(elem, 0) - 1
+        if kwds:
+            self.subtract(kwds)
+
+    def copy(self):
+        'Like dict.copy() but returns a Counter instance instead of a dict.'
+        return Counter(self)
+
+    def __reduce__(self):
+        return self.__class__, (dict(self),)
+
+    def __delitem__(self, elem):
+        'Like dict.__delitem__() but does not raise KeyError for missing values.'
+        if elem in self:
+            super().__delitem__(elem)
+
+    def __repr__(self):
+        if not self:
+            return '%s()' % self.__class__.__name__
+        items = ', '.join(map('%r: %r'.__mod__, self.most_common()))
+        return '%s({%s})' % (self.__class__.__name__, items)
+
+    # Multiset-style mathematical operations discussed in:
+    #       Knuth TAOCP Volume II section 4.6.3 exercise 19
+    #       and at http://en.wikipedia.org/wiki/Multiset
+    #
+    # Outputs guaranteed to only include positive counts.
+    #
+    # To strip negative and zero counts, add-in an empty counter:
+    #       c += Counter()
+
+    def __add__(self, other):
+        '''Add counts from two counters.
+
+        >>> Counter('abbb') + Counter('bcc')
+        Counter({'b': 4, 'c': 2, 'a': 1})
+
+        '''
+        if not isinstance(other, Counter):
+            return NotImplemented
+        result = Counter()
+        for elem in set(self) | set(other):
+            newcount = self[elem] + other[elem]
+            if newcount > 0:
+                result[elem] = newcount
+        return result
+
+    def __sub__(self, other):
+        ''' Subtract count, but keep only results with positive counts.
+
+        >>> Counter('abbbc') - Counter('bccd')
+        Counter({'b': 2, 'a': 1})
+
+        '''
+        if not isinstance(other, Counter):
+            return NotImplemented
+        result = Counter()
+        for elem in set(self) | set(other):
+            newcount = self[elem] - other[elem]
+            if newcount > 0:
+                result[elem] = newcount
+        return result
+
+    def __or__(self, other):
+        '''Union is the maximum of value in either of the input counters.
+
+        >>> Counter('abbb') | Counter('bcc')
+        Counter({'b': 3, 'c': 2, 'a': 1})
+
+        '''
+        if not isinstance(other, Counter):
+            return NotImplemented
+        result = Counter()
+        for elem in set(self) | set(other):
+            p, q = self[elem], other[elem]
+            newcount = q if p < q else p
+            if newcount > 0:
+                result[elem] = newcount
+        return result
+
+    def __and__(self, other):
+        ''' Intersection is the minimum of corresponding counts.
+
+        >>> Counter('abbb') & Counter('bcc')
+        Counter({'b': 1})
+
+        '''
+        if not isinstance(other, Counter):
+            return NotImplemented
+        result = Counter()
+        if len(self) < len(other):
+            self, other = other, self
+        for elem in filter(self.__contains__, other):
+            p, q = self[elem], other[elem]
+            newcount = p if p < q else q
+            if newcount > 0:
+                result[elem] = newcount
+        return result
+
+
+########################################################################
+###  ChainMap (helper for configparser and string.Template)
+########################################################################
+
+class ChainMap(MutableMapping):
+    ''' A ChainMap groups multiple dicts (or other mappings) together
+    to create a single, updateable view.
+
+    The underlying mappings are stored in a list.  That list is public and can
+    accessed or updated using the *maps* attribute.  There is no other state.
+
+    Lookups search the underlying mappings successively until a key is found.
+    In contrast, writes, updates, and deletions only operate on the first
+    mapping.
+
+    '''
+
+    def __init__(self, *maps):
+        '''Initialize a ChainMap by setting *maps* to the given mappings.
+        If no mappings are provided, a single empty dictionary is used.
+
+        '''
+        self.maps = list(maps) or [{}]          # always at least one map
+
+    def __missing__(self, key):
+        raise KeyError(key)
+
+    def __getitem__(self, key):
+        for mapping in self.maps:
+            try:
+                return mapping[key]             # can't use 'key in mapping' with defaultdict
+            except KeyError:
+                pass
+        return self.__missing__(key)            # support subclasses that define __missing__
+
+    def get(self, key, default=None):
+        return self[key] if key in self else default
+
+    def __len__(self):
+        return len(set().union(*self.maps))     # reuses stored hash values if possible
+
+    def __iter__(self):
+        return iter(set().union(*self.maps))
+
+    def __contains__(self, key):
+        return any(key in m for m in self.maps)
+
+    def __bool__(self):
+        return any(self.maps)
+
+    @_recursive_repr()
+    def __repr__(self):
+        return '{0.__class__.__name__}({1})'.format(
+            self, ', '.join(map(repr, self.maps)))
+
+    @classmethod
+    def fromkeys(cls, iterable, *args):
+        'Create a ChainMap with a single dict created from the iterable.'
+        return cls(dict.fromkeys(iterable, *args))
+
+    def copy(self):
+        'New ChainMap or subclass with a new copy of maps[0] and refs to maps[1:]'
+        return self.__class__(self.maps[0].copy(), *self.maps[1:])
+
+    __copy__ = copy
+
+    def new_child(self):                        # like Django's Context.push()
+        'New ChainMap with a new dict followed by all previous maps.'
+        return self.__class__({}, *self.maps)
+
+    @property
+    def parents(self):                          # like Django's Context.pop()
+        'New ChainMap from maps[1:].'
+        return self.__class__(*self.maps[1:])
+
+    def __setitem__(self, key, value):
+        self.maps[0][key] = value
+
+    def __delitem__(self, key):
+        try:
+            del self.maps[0][key]
+        except KeyError:
+            raise KeyError('Key not found in the first mapping: {!r}'.format(key))
+
+    def popitem(self):
+        'Remove and return an item pair from maps[0]. Raise KeyError is maps[0] is empty.'
+        try:
+            return self.maps[0].popitem()
+        except KeyError:
+            raise KeyError('No keys found in the first mapping.')
+
+    def pop(self, key, *args):
+        'Remove *key* from maps[0] and return its value. Raise KeyError if *key* not in maps[0].'
+        try:
+            return self.maps[0].pop(key, *args)
+        except KeyError:
+            raise KeyError('Key not found in the first mapping: {!r}'.format(key))
+
+    def clear(self):
+        'Clear maps[0], leaving maps[1:] intact.'
+        self.maps[0].clear()
+
+
+################################################################################
+### UserDict
+################################################################################
+
+class UserDict(MutableMapping):
+
+    # Start by filling-out the abstract methods
+    def __init__(self, dict=None, **kwargs):
+        self.data = {}
+        if dict is not None:
+            self.update(dict)
+        if len(kwargs):
+            self.update(kwargs)
+    def __len__(self): return len(self.data)
+    def __getitem__(self, key):
+        if key in self.data:
+            return self.data[key]
+        if hasattr(self.__class__, "__missing__"):
+            return self.__class__.__missing__(self, key)
+        raise KeyError(key)
+    def __setitem__(self, key, item): self.data[key] = item
+    def __delitem__(self, key): del self.data[key]
+    def __iter__(self):
+        return iter(self.data)
+
+    # Modify __contains__ to work correctly when __missing__ is present
+    def __contains__(self, key):
+        return key in self.data
+
+    # Now, add the methods in dicts but not in MutableMapping
+    def __repr__(self): return repr(self.data)
+    def copy(self):
+        if self.__class__ is UserDict:
+            return UserDict(self.data.copy())
+        import copy
+        data = self.data
+        try:
+            self.data = {}
+            c = copy.copy(self)
+        finally:
+            self.data = data
+        c.update(self)
+        return c
+    @classmethod
+    def fromkeys(cls, iterable, value=None):
+        d = cls()
+        for key in iterable:
+            d[key] = value
+        return d
+
+
+
+################################################################################
+### UserList
+################################################################################
+
+class UserList(MutableSequence):
+    """A more or less complete user-defined wrapper around list objects."""
+    def __init__(self, initlist=None):
+        self.data = []
+        if initlist is not None:
+            # XXX should this accept an arbitrary sequence?
+            if type(initlist) == type(self.data):
+                self.data[:] = initlist
+            elif isinstance(initlist, UserList):
+                self.data[:] = initlist.data[:]
+            else:
+                self.data = list(initlist)
+    def __repr__(self): return repr(self.data)
+    def __lt__(self, other): return self.data <  self.__cast(other)
+    def __le__(self, other): return self.data <= self.__cast(other)
+    def __eq__(self, other): return self.data == self.__cast(other)
+    def __ne__(self, other): return self.data != self.__cast(other)
+    def __gt__(self, other): return self.data >  self.__cast(other)
+    def __ge__(self, other): return self.data >= self.__cast(other)
+    def __cast(self, other):
+        return other.data if isinstance(other, UserList) else other
+    def __contains__(self, item): return item in self.data
+    def __len__(self): return len(self.data)
+    def __getitem__(self, i): return self.data[i]
+    def __setitem__(self, i, item): self.data[i] = item
+    def __delitem__(self, i): del self.data[i]
+    def __add__(self, other):
+        if isinstance(other, UserList):
+            return self.__class__(self.data + other.data)
+        elif isinstance(other, type(self.data)):
+            return self.__class__(self.data + other)
+        return self.__class__(self.data + list(other))
+    def __radd__(self, other):
+        if isinstance(other, UserList):
+            return self.__class__(other.data + self.data)
+        elif isinstance(other, type(self.data)):
+            return self.__class__(other + self.data)
+        return self.__class__(list(other) + self.data)
+    def __iadd__(self, other):
+        if isinstance(other, UserList):
+            self.data += other.data
+        elif isinstance(other, type(self.data)):
+            self.data += other
+        else:
+            self.data += list(other)
+        return self
+    def __mul__(self, n):
+        return self.__class__(self.data*n)
+    __rmul__ = __mul__
+    def __imul__(self, n):
+        self.data *= n
+        return self
+    def append(self, item): self.data.append(item)
+    def insert(self, i, item): self.data.insert(i, item)
+    def pop(self, i=-1): return self.data.pop(i)
+    def remove(self, item): self.data.remove(item)
+    def clear(self): self.data.clear()
+    def copy(self): return self.data.copy()
+    def count(self, item): return self.data.count(item)
+    def index(self, item, *args): return self.data.index(item, *args)
+    def reverse(self): self.data.reverse()
+    def sort(self, *args, **kwds): self.data.sort(*args, **kwds)
+    def extend(self, other):
+        if isinstance(other, UserList):
+            self.data.extend(other.data)
+        else:
+            self.data.extend(other)
+
+
+
+################################################################################
+### UserString
+################################################################################
+
+class UserString(Sequence):
+    def __init__(self, seq):
+        if isinstance(seq, str):
+            self.data = seq
+        elif isinstance(seq, UserString):
+            self.data = seq.data[:]
+        else:
+            self.data = str(seq)
+    def __str__(self): return str(self.data)
+    def __repr__(self): return repr(self.data)
+    def __int__(self): return int(self.data)
+    def __float__(self): return float(self.data)
+    def __complex__(self): return complex(self.data)
+    def __hash__(self): return hash(self.data)
+
+    def __eq__(self, string):
+        if isinstance(string, UserString):
+            return self.data == string.data
+        return self.data == string
+    def __ne__(self, string):
+        if isinstance(string, UserString):
+            return self.data != string.data
+        return self.data != string
+    def __lt__(self, string):
+        if isinstance(string, UserString):
+            return self.data < string.data
+        return self.data < string
+    def __le__(self, string):
+        if isinstance(string, UserString):
+            return self.data <= string.data
+        return self.data <= string
+    def __gt__(self, string):
+        if isinstance(string, UserString):
+            return self.data > string.data
+        return self.data > string
+    def __ge__(self, string):
+        if isinstance(string, UserString):
+            return self.data >= string.data
+        return self.data >= string
+
+    def __contains__(self, char):
+        if isinstance(char, UserString):
+            char = char.data
+        return char in self.data
+
+    def __len__(self): return len(self.data)
+    def __getitem__(self, index): return self.__class__(self.data[index])
+    def __add__(self, other):
+        if isinstance(other, UserString):
+            return self.__class__(self.data + other.data)
+        elif isinstance(other, str):
+            return self.__class__(self.data + other)
+        return self.__class__(self.data + str(other))
+    def __radd__(self, other):
+        if isinstance(other, str):
+            return self.__class__(other + self.data)
+        return self.__class__(str(other) + self.data)
+    def __mul__(self, n):
+        return self.__class__(self.data*n)
+    __rmul__ = __mul__
+    def __mod__(self, args):
+        return self.__class__(self.data % args)
+
+    # the following methods are defined in alphabetical order:
+    def capitalize(self): return self.__class__(self.data.capitalize())
+    def center(self, width, *args):
+        return self.__class__(self.data.center(width, *args))
+    def count(self, sub, start=0, end=_sys.maxsize):
+        if isinstance(sub, UserString):
+            sub = sub.data
+        return self.data.count(sub, start, end)
+    def encode(self, encoding=None, errors=None): # XXX improve this?
+        if encoding:
+            if errors:
+                return self.__class__(self.data.encode(encoding, errors))
+            return self.__class__(self.data.encode(encoding))
+        return self.__class__(self.data.encode())
+    def endswith(self, suffix, start=0, end=_sys.maxsize):
+        return self.data.endswith(suffix, start, end)
+    def expandtabs(self, tabsize=8):
+        return self.__class__(self.data.expandtabs(tabsize))
+    def find(self, sub, start=0, end=_sys.maxsize):
+        if isinstance(sub, UserString):
+            sub = sub.data
+        return self.data.find(sub, start, end)
+    def format(self, *args, **kwds):
+        return self.data.format(*args, **kwds)
+    def index(self, sub, start=0, end=_sys.maxsize):
+        return self.data.index(sub, start, end)
+    def isalpha(self): return self.data.isalpha()
+    def isalnum(self): return self.data.isalnum()
+    def isdecimal(self): return self.data.isdecimal()
+    def isdigit(self): return self.data.isdigit()
+    def isidentifier(self): return self.data.isidentifier()
+    def islower(self): return self.data.islower()
+    def isnumeric(self): return self.data.isnumeric()
+    def isspace(self): return self.data.isspace()
+    def istitle(self): return self.data.istitle()
+    def isupper(self): return self.data.isupper()
+    def join(self, seq): return self.data.join(seq)
+    def ljust(self, width, *args):
+        return self.__class__(self.data.ljust(width, *args))
+    def lower(self): return self.__class__(self.data.lower())
+    def lstrip(self, chars=None): return self.__class__(self.data.lstrip(chars))
+    def partition(self, sep):
+        return self.data.partition(sep)
+    def replace(self, old, new, maxsplit=-1):
+        if isinstance(old, UserString):
+            old = old.data
+        if isinstance(new, UserString):
+            new = new.data
+        return self.__class__(self.data.replace(old, new, maxsplit))
+    def rfind(self, sub, start=0, end=_sys.maxsize):
+        if isinstance(sub, UserString):
+            sub = sub.data
+        return self.data.rfind(sub, start, end)
+    def rindex(self, sub, start=0, end=_sys.maxsize):
+        return self.data.rindex(sub, start, end)
+    def rjust(self, width, *args):
+        return self.__class__(self.data.rjust(width, *args))
+    def rpartition(self, sep):
+        return self.data.rpartition(sep)
+    def rstrip(self, chars=None):
+        return self.__class__(self.data.rstrip(chars))
+    def split(self, sep=None, maxsplit=-1):
+        return self.data.split(sep, maxsplit)
+    def rsplit(self, sep=None, maxsplit=-1):
+        return self.data.rsplit(sep, maxsplit)
+    def splitlines(self, keepends=0): return self.data.splitlines(keepends)
+    def startswith(self, prefix, start=0, end=_sys.maxsize):
+        return self.data.startswith(prefix, start, end)
+    def strip(self, chars=None): return self.__class__(self.data.strip(chars))
+    def swapcase(self): return self.__class__(self.data.swapcase())
+    def title(self): return self.__class__(self.data.title())
+    def translate(self, *args):
+        return self.__class__(self.data.translate(*args))
+    def upper(self): return self.__class__(self.data.upper())
+    def zfill(self, width): return self.__class__(self.data.zfill(width))
+
+
+
+################################################################################
+### Simple tests
+################################################################################
+
+if __name__ == '__main__':
+    # verify that instances can be pickled
+    from pickle import loads, dumps
+    Point = namedtuple('Point', 'x, y', True)
+    p = Point(x=10, y=20)
+    assert p == loads(dumps(p))
+
+    # test and demonstrate ability to override methods
+    class Point(namedtuple('Point', 'x y')):
+        __slots__ = ()
+        @property
+        def hypot(self):
+            return (self.x ** 2 + self.y ** 2) ** 0.5
+        def __str__(self):
+            return 'Point: x=%6.3f  y=%6.3f  hypot=%6.3f' % (self.x, self.y, self.hypot)
+
+    for p in Point(3, 4), Point(14, 5/7.):
+        print (p)
+
+    class Point(namedtuple('Point', 'x y')):
+        'Point class with optimized _make() and _replace() without error-checking'
+        __slots__ = ()
+        _make = classmethod(tuple.__new__)
+        def _replace(self, _map=map, **kwds):
+            return self._make(_map(kwds.get, ('x', 'y'), self))
+
+    print(Point(11, 22)._replace(x=100))
+
+    Point3D = namedtuple('Point3D', Point._fields + ('z',))
+    print(Point3D.__doc__)
+
+    import doctest
+    TestResults = namedtuple('TestResults', 'failed attempted')
+    print(TestResults(*doctest.testmod()))