def opt_ignore_ext(self, ext):
        """
        Specify an extension to ignore.  These will be processed in order.
        """
        if not isinstance(self['root'], static.File):
            raise usage.UsageError("You can only use --ignore_ext "
                                   "after --path.")
        self['root'].ignoreExt(ext)

        Specify an extension to ignore.  These will be processed in order.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/tap.py