<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def contains(self, key):
        "Exact matching."
        index = self.follow_bytes(key, self.ROOT)
        if index is None:
            return False
        return self.has_value(index)