keyedlist.py

"""KeyedList : A list that can also be accessed using a (string) key like a dict

A mutable alternative to namedtuple, yet a lot simpler than the full featured 'namedlist' class

Intended for use like a C struct with writeable fields

"""

class KeyedList(list):
    """A list that can also be accessed using a (string) key like a dict.
    Appending to the list appends a value with no key.
    Sorting the list sorts the values, NOT the keys.
    
    # Initialise it with a list of (key, value) tuples
    >>> l = KeyedList([('one', 1), ('two', 2), ('foo', 23), ('bar', 9)])
    >>> l
    [1, 2, 23, 9]
    
    >>> len(l)
    4
    
    # Replace the whole list using [:], (otherwise new list has no keys!)
    >>> l[:] = (9,8,7,6)
    >>> l
    [9, 8, 7, 6]

    # Access using index or key
    >>> l[0]
    9
    >>> l['two']
    8
    
    # or by slice
    >>> l[0:2]
    [9, 8]
    
    # Update using index or key
    >>> l[3] = 5
    >>> l['foo'] = 0
    >>> l
    [9, 8, 0, 5]
    
    # Accessing items beyond the end of the list gives an IndexError
    >>> l[4] = 99
    Traceback (most recent call last):
    ...
    IndexError: list assignment index out of range
    
    >>> l['bad'] = 97
    Traceback (most recent call last):
    ...
    IndexError: bad
    
    # It is possible to append to the list, but appended items have no keys
    >>> l.append(20)
    >>> l
    [9, 8, 0, 5, 20]
    
    """
    def __init__(self, kvlist):
        self._keys = [kv[0] for kv in kvlist]
        list.__init__(self, [kv[1] for kv in kvlist])
        #self._values = [kv[1] for kv in kvlist]

    def __getitem__(self, i):
        if isinstance(i, (int, slice)):
            return list.__getitem__(self, i)
        elif self._keys and i in self._keys:
            return list.__getitem__(self, self._keys.index(i))
        else:
            raise IndexError(str(i))

    def __setitem__(self, i, val):
        if isinstance(i, (int, slice)):
            list.__setitem__(self, i, val)
        elif self._keys and i in self._keys:
            list.__setitem__(self, self._keys.index(i), val)
        else:
            raise IndexError(str(i))


if __name__ == '__main__':
    import doctest
    doctest.testmod()