:param category: application|audio|image|message|model|multipart|text|video

def mime_type(self, category=None):
        """
        :param category: application|audio|image|message|model|multipart|text|video
        """
        category = category if category else self.random_element(
            list(self.mime_types.keys()))
        return self.random_element(self.mime_types[category])