def opt_processor(self, proc):
        """
        `ext=class' where `class' is added as a Processor for files ending
        with `ext'.
        """
        if not isinstance(self['root'], static.File):
            raise usage.UsageError(
                "You can only use --processor after --path.")
        ext, klass = proc.split('=', 1)
        self['root'].processors[ext] = reflect.namedClass(klass)

        `ext=class' where `class' is added as a Processor for files ending
        with `ext'.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/tap.py