# move it to utils.py
# also look at frozensets
# look at import collections - lot of good data structures
# learn about co-routines (returning generators from generators i.e. yield
# statement)


class uniquelist(list):

    ''' A list whose every value is unique.
    uniquelist.append(val) or __setitem__(pos,val) i.e. uniquelist[pos]=val is ignored if val is already in uniquelist.
    Returns True if the value is added, else returns False. '''

    def __setitem__(self, pos, val):
        if val not in self:
            super(uniquelist, self).__setitem__(pos, val)
            return True
        else:
            return False

    def append(self, val):
        if val not in self:
            super(uniquelist, self).append(val)
            return True
        else:
            return False

    def extend(self, iterable):
        # todo: use yield so that it is not copied into memory
        for temp in iterable:
            self.append(temp)
    # Todo: Allow for type checking by allowing a type_of_members to be set