Python Ordered Dictinary

ordict.py

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

'''
    Ordered dict
    http://ak.net84.net/projects/python-ordered-dictionary/
    
    Example usage:
    
    >>> o = Ordict( ('abc', 123), ('def', '456', 3) )
    >>> o['ghi'] = '789'
    >>> o['jkl'] = 987
    >>> o['mno'] = '654' # replaces index 3
    >>> o.set('pqr', 321, 5)
    >>> print o
    Ordict {0: ['abc', 123], 1: ['ghi', '789'], 2: ['jkl', 987], 3: ['mno', '654'], 5: ['pqr', 321]}
    >>> print o.item_at(2)
    ['jkl', 987]
    
'''
class Ordict(dict):
    def __init__(self, *args, **kwargs):
        self.ordered_items = {} # {0:('a':'b'), 4:('c','d')...}
        self.item_to_order = {} # {'a':0, 'c':4}
        self.next_index = 0 # The next available index
        for item in args:
            if len(item) > 3:
                raise Exception('Ordered items must be tuples: (key , value [, index])')
            elif len(item) == 2:
                self.__setitem__(item[0], item[1])
            elif len(item) == 3:
                if item[2] < 0:
                    raise Exception('Index must be given as a positive integer')
                self.__setitem__(item[0], item[1], item[2])
        return dict.__init__(self, **kwargs)
    
    def __getitem__(self, key):
        return dict.__getitem__(self, str(key))
    
    def __setitem__(self, key, value, index=None):
        key = str(key)
        _index = self.next_index
        if type(index) is int:
            _index = abs(index)
            # Find next available index. If current next_index is untaken, keep it.
            # If this set took it, increment
            if _index == self.next_index:
                self.next_index += 1
        else:
            self.next_index += 1 # increment index
        self.ordered_items[_index] = [key, value]
        self.item_to_order[key] = _index
        dict.__setitem__(self, key, value)
    
    def __delitem__(self, key):
        key = str(key)
        index = self.item_to_order[key]
        del self.ordered_items[index]
        return dict.__delitem__(self, key)
    
    def __iter__(self):
        for index in self.ordered_items:
            item = self.ordered_items[index]
            yield item[0]
    
    def __repr__(self):
        return 'Ordict ' + self.ordered_items.__repr__()
    
    def set(self, key, value, index=None):
        '''
        Set the key:value with optional index
        '''
        return self.__setitem__(key, value, index)
    
    def index_of(self, key, default=None):
        '''
        Return index of key or 'default' if it doesn't exist
        '''
        key = str(key)
        return self.item_to_order[key] if key in self.item_to_order else default
    
    def item_at(self, index, default=None):
        '''
        Return item at index as a tuple or 'default' if it doesn't exist
        '''
        index = int(index)
        item = self.ordered_items[index] if index in self.ordered_items else None
        if item:
            return item
        else:
            return default
    
    def key_at(self, index, default=None):
        '''
        Return key at index or 'default' if it doesn't exist
        '''
        index = int(index)
        item = self.item_at(index)
        if item:
            return item[0]
        else:
            return default
    
    def value_at(self, index, default=None):
        '''
        Return value at index or 'default' if it doesn't exist
        '''
        index = int(index)
        item = self.item_at(index)
        if item:
            return item[1]
        else:
            return default