<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def hash160(self, is_compressed=None):
 """ Return the hash160 representation of this key, if available. """

        if is_compressed is None:
            is_compressed = self.is_compressed()
        if is_compressed:
            if self._hash160_compressed is None:
                self._hash160_compressed = hash160(self.sec(is_compressed=is_compressed))
            return self._hash160_compressed

        if self._hash160_uncompressed is None:
            self._hash160_uncompressed = hash160(self.sec(is_compressed=is_compressed))
        return self._hash160_uncompressed