def value(self):
        """
        Get/set the value of this element, using the ``value`` attribute.

        Also, if this is a checkbox and it has no value, this defaults
        to ``'on'``.  If it is a checkbox or radio that is not
        checked, this returns None.
        """
        if self.checkable:
            if self.checked:
                return self.get('value') or 'on'
            else:
                return None
        return self.get('value')

        Get/set the value of this element, using the ``value`` attribute.

        Also, if this is a checkbox and it has no value, this defaults
        to ``'on'``.  If it is a checkbox or radio that is not
        checked, this returns None.
        
stackoverflow/venv/lib/python3.6/site-packages/lxml/html/__init__.py