问Python3: gzip.open()和模式

EN

def open(filename, mode="rb", compresslevel=9,
         encoding=None, errors=None, newline=None):
    """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 9.
    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).
    """
    if "t" in mode:
        if "b" in mode:
            raise ValueError("Invalid mode: %r" % (mode,))
    else:
        if encoding is not None:
            raise ValueError("Argument 'encoding' not supported in binary mode")
        if errors is not None:
            raise ValueError("Argument 'errors' not supported in binary mode")
        if newline is not None:
            raise ValueError("Argument 'newline' not supported in binary mode")

    gz_mode = mode.replace("t", "")
    if isinstance(filename, (str, bytes, os.PathLike)):
        binary_file = GzipFile(filename, gz_mode, compresslevel)
    elif hasattr(filename, "read") or hasattr(filename, "write"):
        binary_file = GzipFile(None, gz_mode, compresslevel, filename)
    else:
        raise TypeError("filename must be a str or bytes object, or a file")

    if "t" in mode:
        return io.TextIOWrapper(binary_file, encoding, errors, newline)
    else:
        return binary_file  

 if mode and ('t' in mode or 'U' in mode):
        raise ValueError("Invalid mode: {!r}".format(mode))
    if mode and 'b' not in mode:
        mode += 'b'
    if fileobj is None:
        fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
    if filename is None:
        filename = getattr(fileobj, 'name', '')
        if not isinstance(filename, (str, bytes)):
            filename = ''
    else:
        filename = os.fspath(filename)
    if mode is None:
        mode = getattr(fileobj, 'mode', 'rb')

if mode and 'b' not in mode:
            mode += 'b'