def valid_conkey(self, conkey):
        """Check that the conkey is a valid one. Return True if valid. A
        condition key is valid if it is one in the _COND_PREFIXES
        list. With the prefix removed, the remaining string must be
        either a number or the empty string."""

        for prefix in _COND_PREFIXES:
            trailing = conkey.lstrip(prefix)
            if trailing == '' and conkey:  # conkey is not empty
                return True
            try:
                int(trailing)
                return True
            except ValueError:
                pass

        return False
Check that the conkey is a valid one. Return True if valid. A
        condition key is valid if it is one in the _COND_PREFIXES
        list. With the prefix removed, the remaining string must be
        either a number or the empty string.