'remove only most current key-entry'

def __delitem__(self, key):

    key = self.key(key)
    if (key in self.data_with_same_key):
        if (len(self.data_with_same_key[key]) == 1):
            self.data[key] = self.data_with_same_key.pop(key)[0]
        else:
            self.data[key] = self.data_with_same_key[key].pop((-1))
    else:
        del self.data[key]
