<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def namespace_for_prefix(self, prefix):
 """Get the namespace the given prefix maps to. Args: prefix (str):
 The prefix Returns: str: The namespace, or None if the prefix isn't mapped to anything in this set. """

        try:
            ni = self.__lookup_prefix(prefix)
        except PrefixNotFoundError:
            return None
        else:
            return ni.uri