datastructures.py

# -*- coding: utf-8 -*-

from types import GeneratorType

class SortedDict(dict):
    """
    A dictionary that keeps its keys in the order in which they're inserted.
    """
    def __new__(cls, *args, **kwargs):
        instance = super(SortedDict, cls).__new__(cls, *args, **kwargs)
        instance.keyOrder = []
        return instance

    def __init__(self, data=None):
        if data is None:
            data = {}
        elif isinstance(data, GeneratorType):
            # Unfortunately we need to be able to read a generator twice.  Once
            # to get the data into self with our super().__init__ call and a
            # second time to setup keyOrder correctly
            data = list(data)
        super(SortedDict, self).__init__(data)
        if isinstance(data, dict):
            self.keyOrder = data.keys()
        else:
            self.keyOrder = []
            seen = set()
            for key, value in data:
                if key not in seen:
                    self.keyOrder.append(key)
                    seen.add(key)

    def __deepcopy__(self, memo):
        return self.__class__([(key, deepcopy(value, memo))
                               for key, value in self.iteritems()])

    def __setitem__(self, key, value):
        if key not in self:
            self.keyOrder.append(key)
        super(SortedDict, self).__setitem__(key, value)

    def __delitem__(self, key):
        super(SortedDict, self).__delitem__(key)
        self.keyOrder.remove(key)

    def __iter__(self):
        return iter(self.keyOrder)

    def pop(self, k, *args):
        result = super(SortedDict, self).pop(k, *args)
        try:
            self.keyOrder.remove(k)
        except ValueError:
            # Key wasn't in the dictionary in the first place. No problem.
            pass
        return result

    def popitem(self):
        result = super(SortedDict, self).popitem()
        self.keyOrder.remove(result[0])
        return result

    def items(self):
        return zip(self.keyOrder, self.values())

    def iteritems(self):
        for key in self.keyOrder:
            yield key, self[key]

    def keys(self):
        return self.keyOrder[:]

    def iterkeys(self):
        return iter(self.keyOrder)

    def values(self):
        return map(self.__getitem__, self.keyOrder)

    def itervalues(self):
        for key in self.keyOrder:
            yield self[key]

    def update(self, dict_):
        for k, v in dict_.iteritems():
            self[k] = v

    def setdefault(self, key, default):
        if key not in self:
            self.keyOrder.append(key)
        return super(SortedDict, self).setdefault(key, default)

    def value_for_index(self, index):
        """Returns the value of the item at the given zero-based index."""
        return self[self.keyOrder[index]]

    def insert(self, index, key, value):
        """Inserts the key, value pair before the item with the given index."""
        if key in self.keyOrder:
            n = self.keyOrder.index(key)
            del self.keyOrder[n]
            if n < index:
                index -= 1
        self.keyOrder.insert(index, key)
        super(SortedDict, self).__setitem__(key, value)

    def copy(self):
        """Returns a copy of this object."""
        # This way of initializing the copy means it works for subclasses, too.
        obj = self.__class__(self)
        obj.keyOrder = self.keyOrder[:]
        return obj

    def __repr__(self):
        """
        Replaces the normal dict.__repr__ with a version that returns the keys
        in their sorted order.
        """
        return '{%s}' % ', '.join(['%r: %r' % (k, v) for k, v in self.items()])

    def clear(self):
        super(SortedDict, self).clear()
        self.keyOrder = []