'defines self[key] = value'

def __setitem__(self, key, value):

    key = self.key(key)
    if (key in self.data_with_same_key):
        self.data_with_same_key[key] += [self.data[key]]
    elif (key in self.data):
        self.data_with_same_key[key] = [self.data[key]]
    self.data[key] = value
