✏ EDIT: UserDict.py

"""A more or less complete user-defined wrapper around dictionary objects."""

class UserDict:
    def __init__(*args, **kwargs):
        if not args:
            raise TypeError("descriptor '__init__' of 'UserDict' object "
                            "needs an argument")
        self = args[0]
        args = args[1:]
        if len(args) > 1:
            raise TypeError('expected at most 1 arguments, got %d' % len(args))
        if args:
            dict = args[0]
        elif 'dict' in kwargs:
            dict = kwargs.pop('dict')
            import warnings
            warnings.warn("Passing 'dict' as keyword argument is "
                          "deprecated", PendingDeprecationWarning,
                          stacklevel=2)
        else:
            dict = None
        self.data = {}
        if dict is not None:
            self.update(dict)
        if len(kwargs):
            self.update(kwargs)
    def __repr__(self): return repr(self.data)
    def __cmp__(self, dict):
        if isinstance(dict, UserDict):
            return cmp(self.data, dict.data)
        else:
            return cmp(self.data, dict)
    __hash__ = None # Avoid Py3k warning
    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 clear(self): self.data.clear()
    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
    def keys(self): return self.data.keys()
    def items(self): return self.data.items()
    def iteritems(self): return self.data.iteritems()
    def iterkeys(self): return self.data.iterkeys()
    def itervalues(self): return self.data.itervalues()
    def values(self): return self.data.values()
    def has_key(self, key): return key in self.data
    def update(*args, **kwargs):
        if not args:
            raise TypeError("descriptor 'update' of 'UserDict' object "
                            "needs an argument")
        self = args[0]
        args = args[1:]
        if len(args) > 1:
            raise TypeError('expected at most 1 arguments, got %d' % len(args))
        if args:
            dict = args[0]
        elif 'dict' in kwargs:
            dict = kwargs.pop('dict')
            import warnings
            warnings.warn("Passing 'dict' as keyword argument is deprecated",
                          PendingDeprecationWarning, stacklevel=2)
        else:
            dict = None
        if dict is None:
            pass
        elif isinstance(dict, UserDict):
            self.data.update(dict.data)
        elif isinstance(dict, type({})) or not hasattr(dict, 'items'):
            self.data.update(dict)
        else:
            for k, v in dict.items():
                self[k] = v
        if len(kwargs):
            self.data.update(kwargs)
    def get(self, key, failobj=None):
        if key not in self:
            return failobj
        return self[key]
    def setdefault(self, key, failobj=None):
        if key not in self:
            self[key] = failobj
        return self[key]
    def pop(self, key, *args):
        return self.data.pop(key, *args)
    def popitem(self):
        return self.data.popitem()
    def __contains__(self, key):
        return key in self.data
    @classmethod
    def fromkeys(cls, iterable, value=None):
        d = cls()
        for key in iterable:
            d[key] = value
        return d

class IterableUserDict(UserDict):
    def __iter__(self):
        return iter(self.data)

import _abcoll
_abcoll.MutableMapping.register(IterableUserDict)

class DictMixin:
    # Mixin defining all dictionary methods for classes that already have
    # a minimum dictionary interface including getitem, setitem, delitem,
    # and keys. Without knowledge of the subclass constructor, the mixin
    # does not define __init__() or copy().  In addition to the four base
    # methods, progressively more efficiency comes with defining
    # __contains__(), __iter__(), and iteritems().

# second level definitions support higher levels
    def __iter__(self):
        for k in self.keys():
            yield k
    def has_key(self, key):
        try:
            self[key]
        except KeyError:
            return False
        return True
    def __contains__(self, key):
        return self.has_key(key)

# third level takes advantage of second level definitions
    def iteritems(self):
        for k in self:
            yield (k, self[k])
    def iterkeys(self):
        return self.__iter__()

# fourth level uses definitions from lower levels
    def itervalues(self):
        for _, v in self.iteritems():
            yield v
    def values(self):
        return [v for _, v in self.iteritems()]
    def items(self):
        return list(self.iteritems())
    def clear(self):
        for key in self.keys():
            del self[key]
    def setdefault(self, key, default=None):
        try:
            return self[key]
        except KeyError:
            self[key] = default
        return default
    def pop(self, key, *args):
        if len(args) > 1:
            raise TypeError, "pop expected at most 2 arguments, got "\
                              + repr(1 + len(args))
        try:
            value = self[key]
        except KeyError:
            if args:
                return args[0]
            raise
        del self[key]
        return value
    def popitem(self):
        try:
            k, v = self.iteritems().next()
        except StopIteration:
            raise KeyError, 'container is empty'
        del self[k]
        return (k, v)
    def update(self, other=None, **kwargs):
        # Make progressively weaker assumptions about "other"
        if other is None:
            pass
        elif hasattr(other, 'iteritems'):  # iteritems saves memory and lookups
            for k, v in other.iteritems():
                self[k] = v
        elif hasattr(other, 'keys'):
            for k in other.keys():
                self[k] = other[k]
        else:
            for k, v in other:
                self[k] = v
        if kwargs:
            self.update(kwargs)
    def get(self, key, default=None):
        try:
            return self[key]
        except KeyError:
            return default
    def __repr__(self):
        return repr(dict(self.iteritems()))
    def __cmp__(self, other):
        if other is None:
            return 1
        if isinstance(other, DictMixin):
            other = dict(other.iteritems())
        return cmp(dict(self.iteritems()), other)
    def __len__(self):
        return len(self.keys())

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