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

def check_required_keys(self, required_keys):
        '''raise InsufficientGraftMPackageException if this package does not
        conform to the standard of the given package'''
        h = self._contents_hash
        for key in required_keys:
            if key not in h:
                raise InsufficientGraftMPackageException("Package missing key %s" % key)