# Τεκμηρίωση του Django - 1.10.7

# Πηγαίος κώδικας για το django.utils.datastructures

    import copy
    from collections import OrderedDict

    from django.utils import six

    class OrderedSet(object):
        """
        A set which keeps the ordering of the inserted items.
        Currently backs onto OrderedDict.
        """

        def __init__(self, iterable=None):
            self.dict = OrderedDict(((x, None) for x in iterable) if iterable else [])

        def add(self, item):
            self.dict[item] = None

        def remove(self, item):
            del self.dict[item]

        def discard(self, item):
            try:
                self.remove(item)
            except KeyError:
                pass

        def __iter__(self):
            return iter(self.dict.keys())

        def __contains__(self, item):
            return item in self.dict

        def __bool__(self):
            return bool(self.dict)

        def __nonzero__(self):      # Python 2 compatibility
            return type(self).__bool__(self)

        def __len__(self):
            return len(self.dict)

    class MultiValueDictKeyError(KeyError):
        pass

    class MultiValueDict(dict):
        """
        A subclass of dictionary customized to handle multiple values for the
        same key.

        >>> d = MultiValueDict({'name': ['Adrian', 'Simon'], 'position': ['Developer']})
        >>> d['name']
        'Simon'
        >>> d.getlist('name')
        ['Adrian', 'Simon']
        >>> d.getlist('doesnotexist')
        []
        >>> d.getlist('doesnotexist', ['Adrian', 'Simon'])
        ['Adrian', 'Simon']
        >>> d.get('lastname', 'nonexistent')
        'nonexistent'
        >>> d.setlist('lastname', ['Holovaty', 'Willison'])

        This class exists to solve the irritating problem raised by cgi.parse_qs,
        which returns a list for every key, even though most Web forms submit
        single name-value pairs.
        """
        def __init__(self, key_to_list_mapping=()):
            super(MultiValueDict, self).__init__(key_to_list_mapping)

        def __repr__(self):
            return "<%s: %s>" % (self.__class__.__name__,
                                 super(MultiValueDict, self).__repr__())

        def __getitem__(self, key):
            """
            Returns the last data value for this key, or [] if it's an empty list;
            raises KeyError if not found.
            """
            try:
                list_ = super(MultiValueDict, self).__getitem__(key)
            except KeyError:
                raise MultiValueDictKeyError(repr(key))
            try:
                return list_[-1]
            except IndexError:
                return []

        def __setitem__(self, key, value):
            super(MultiValueDict, self).__setitem__(key, [value])

        def __copy__(self):
            return self.__class__([
                (k, v[:])
                for k, v in self.lists()
            ])

        def __deepcopy__(self, memo=None):
            if memo is None:
                memo = {}
            result = self.__class__()
            memo[id(self)] = result
            for key, value in dict.items(self):
                dict.__setitem__(result, copy.deepcopy(key, memo),
                                 copy.deepcopy(value, memo))
            return result

        def __getstate__(self):
            obj_dict = self.__dict__.copy()
            obj_dict['_data'] = {k: self.getlist(k) for k in self}
            return obj_dict

        def __setstate__(self, obj_dict):
            data = obj_dict.pop('_data', {})
            for k, v in data.items():
                self.setlist(k, v)
            self.__dict__.update(obj_dict)

        def get(self, key, default=None):
            """
            Returns the last data value for the passed key. If key doesn't exist
            or value is an empty list, then default is returned.
            """
            try:
                val = self[key]
            except KeyError:
                return default
            if val == []:
                return default
            return val

        def getlist(self, key, default=None):
            """
            Returns the list of values for the passed key. If key doesn't exist,
            then a default value is returned.
            """
            try:
                return super(MultiValueDict, self).__getitem__(key)
            except KeyError:
                if default is None:
                    return []
                return default

        def setlist(self, key, list_):
            super(MultiValueDict, self).__setitem__(key, list_)

        def setdefault(self, key, default=None):
            if key not in self:
                self[key] = default
                # Do not return default here because __setitem__() may store
                # another value -- QueryDict.__setitem__() does. Look it up.
            return self[key]

        def setlistdefault(self, key, default_list=None):
            if key not in self:
                if default_list is None:
                    default_list = []
                self.setlist(key, default_list)
                # Do not return default_list here because setlist() may store
                # another value -- QueryDict.setlist() does. Look it up.
            return self.getlist(key)

        def appendlist(self, key, value):
            """Appends an item to the internal list associated with key."""
            self.setlistdefault(key).append(value)

        def _iteritems(self):
            """
            Yields (key, value) pairs, where value is the last item in the list
            associated with the key.
            """
            for key in self:
                yield key, self[key]

        def _iterlists(self):
            """Yields (key, list) pairs."""
            return six.iteritems(super(MultiValueDict, self))

        def _itervalues(self):
            """Yield the last value on every key list."""
            for key in self:
                yield self[key]

        if six.PY3:
            items = _iteritems
            lists = _iterlists
            values = _itervalues
        else:
            iteritems = _iteritems
            iterlists = _iterlists
            itervalues = _itervalues

            def items(self):
                return list(self.iteritems())

            def lists(self):
                return list(self.iterlists())

            def values(self):
                return list(self.itervalues())

        def copy(self):
            """Returns a shallow copy of this object."""
            return copy.copy(self)

        def update(self, *args, **kwargs):
            """
            update() extends rather than replaces existing key lists.
            Also accepts keyword args.
            """
            if len(args) > 1:
                raise TypeError("update expected at most 1 arguments, got %d" % len(args))
            if args:
                other_dict = args[0]
                if isinstance(other_dict, MultiValueDict):
                    for key, value_list in other_dict.lists():
                        self.setlistdefault(key).extend(value_list)
                else:
                    try:
                        for key, value in other_dict.items():
                            self.setlistdefault(key).append(value)
                    except TypeError:
                        raise ValueError("MultiValueDict.update() takes either a MultiValueDict or dictionary")
            for key, value in six.iteritems(kwargs):
                self.setlistdefault(key).append(value)

        def dict(self):
            """
            Returns current object as a dict with singular values.
            """
            return {key: self[key] for key in self}

    class ImmutableList(tuple):
        """
        A tuple-like object that raises useful errors when it is asked to mutate.

        Example::

            >>> a = ImmutableList(range(5), warning="You cannot mutate this.")
            >>> a[3] = '4'
            Traceback (most recent call last):
                ...
            AttributeError: You cannot mutate this.
        """

        def __new__(cls, *args, **kwargs):
            if 'warning' in kwargs:
                warning = kwargs['warning']
                del kwargs['warning']
            else:
                warning = 'ImmutableList object is immutable.'
            self = tuple.__new__(cls, *args, **kwargs)
            self.warning = warning
            return self

        def complain(self, *wargs, **kwargs):
            if isinstance(self.warning, Exception):
                raise self.warning
            else:
                raise AttributeError(self.warning)

        # All list mutation functions complain.
        __delitem__ = complain
        __delslice__ = complain
        __iadd__ = complain
        __imul__ = complain
        __setitem__ = complain
        __setslice__ = complain
        append = complain
        extend = complain
        insert = complain
        pop = complain
        remove = complain
        sort = complain
        reverse = complain

    class DictWrapper(dict):
        """
        Wraps accesses to a dictionary so that certain values (those starting with
        the specified prefix) are passed through a function before being returned.
        The prefix is removed before looking up the real value.

        Used by the SQL construction code to ensure that values are correctly
        quoted before being used.
        """
        def __init__(self, data, func, prefix):
            super(DictWrapper, self).__init__(data)
            self.func = func
            self.prefix = prefix

        def __getitem__(self, key):
            """
            Retrieves the real value after stripping the prefix string (if
            present). If the prefix is present, pass the value through self.func
            before returning, otherwise return the raw value.
            """
            if key.startswith(self.prefix):
                use_func = True
                key = key[len(self.prefix):]
            else:
                use_func = False
            value = super(DictWrapper, self).__getitem__(key)
            if use_func:
                return self.func(value)
            return value