def opt_mime_type(self, defaultType):
        """
        Specify the default mime-type for static files.
        """
        if not isinstance(self['root'], static.File):
            raise usage.UsageError(
                "You can only use --mime_type after --path.")
        self['root'].defaultType = defaultType

        Specify the default mime-type for static files.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/tap.py