Open a gzip-compressed file in binary or text mode. The filename argument can be an actual filename (a str or bytes object), or an existing file object to read from or write to. The mode argument can be "r", "rb", "w", "wb", "x", "xb", "a" or "ab" for binary mode, or "rt", "wt", "xt" or "at" for text mode. The default mode is "rb", and the default compresslevel is 6. For binary mode, this function is equivalent to the GzipFile constructor: GzipFile(filename, mode, compresslevel). In this case, the encoding, errors and newline arguments must not be provided. For text mode, a GzipFile object is created, and wrapped in an io.TextIOWrapper instance with the specified encoding, error handling behavior, and line ending(s).