A function called dict_invert that takes in a dictionary with immutable values and returns the inverse of the dictionary. The inverse of a dictionary d is another dictionary whose keys are the unique dictionary values in d. The value for a key in the inverse dictionary is a sorted list of all keys in d that have the same value in d.

inversedictionary.py

def dict_invert(d):
    '''
    d: dict
    Returns an inverted dictionary according to the instructions above
    '''
    inv_map = {}
    for k, v in d.iteritems():
        inv_map[v] = inv_map.get(v, [])
        inv_map[v].append(k)
        inv_map[v] = sorted(inv_map[v])
    return inv_map