def get_local(self, variable_name):
        '''
        Return the value of the local variable. Raises UnknownVariable is
        the name is not known.
        '''
        if variable_name not in self._locals:
            raise UnknownVariable('Unknown variable %s' % variable_name)
        return self._locals[variable_name]
Return the value of the local variable. Raises UnknownVariable is
        the name is not known.