Given the fully-qualified name and a sender's script pubkey,
        determine if the sender owns the name.

        The name must exist and not be revoked or expired at the
        current block.

def is_name_owner( self, name, sender_script_pubkey ):
        """
        Given the fully-qualified name and a sender's script pubkey,
        determine if the sender owns the name.

        The name must exist and not be revoked or expired at the
        current block.
        """
        if not self.is_name_registered( name ):
            # no one owns it 
            return False 

        owner = self.get_name_owner( name )
        if owner != sender_script_pubkey:
            return False 
        else:
            return True