def __rxor__(self, other ):
        """
        Implementation of ^ operator when left operand is not a C{L{ParserElement}}
        """
        if isinstance( other, basestring ):
            other = ParserElement._literalStringClass( other )
        if not isinstance( other, ParserElement ):
            warnings.warn("Cannot combine element of type %s with ParserElement" % type(other),
                    SyntaxWarning, stacklevel=2)
            return None
        return other ^ self

        Implementation of ^ operator when left operand is not a C{L{ParserElement}}
        
src/pkg_resources/_vendor/pyparsing.py