def METHOD_NAME(cls, mime_type):
    """
    Guess a file extension (with a leading dot) given its mime type. If no
    file is found, return an empty extension.
    """
    if mime_type in cls.FILE_EXTENSIONS_BY_TYPE:
        return cls.FILE_EXTENSIONS_BY_TYPE[mime_type]
    return mimetypes.METHOD_NAME(mime_type) or ''