def remove(self, value):
        """
        Remove a class; it must currently be present.

        If the class is not present, raise a KeyError.
        """
        if not value or re.search(r'\s', value):
            raise ValueError("Invalid class name: %r" % value)
        super(Classes, self).remove(value)

        Remove a class; it must currently be present.

        If the class is not present, raise a KeyError.
        
stackoverflow/venv/lib/python3.6/site-packages/lxml/html/__init__.py