docs: def get_filter(cls, mimetype):
          """
          Returns a filter string for the file dialog. The filter is based
          on the mime type.
  
          :param mimetype: path from which the filter must be derived.
          :return: Filter string
          """
          filters = ' '.join(
              ['*%s' % ext for ext in mimetypes.guess_all_extensions(mimetype)])
          return '%s (%s)' % (mimetype, filters)