<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _has(self, key, exact=0):
 """Raises an exception if key is ambiguous"""

        if not exact:
            key = self.getfullkey(key,new=1)
        return key in self.data