'Constructor for the GzipFile class.
At least one of fileobj and filename must be given a
non-trivial value.
The new class instance is based on fileobj, which can be a regular
file, an io.BytesIO object, or any other object which simulates a file.
It defaults to None, in which case filename is opened to provide
a file object.
When fileobj is not None, the filename argument is only used to be
included in the gzip file header, which may include the original
filename of the uncompressed file.  It defaults to the filename of
fileobj, if discernible; otherwise, it defaults to the empty string,
and in this case the original filename is not included in the header.
The mode argument can be any of \'r\', \'rb\', \'a\', \'ab\', \'w\', \'wb\', \'x\', or
\'xb\' depending on whether the file will be read or written.  The default
is the mode of fileobj if discernible; otherwise, the default is \'rb\'.
A mode of \'r\' is equivalent to one of \'rb\', and similarly for \'w\' and
\'wb\', \'a\' and \'ab\', and \'x\' and \'xb\'.
The compresslevel argument is an integer from 0 to 9 controlling the
level of compression; 1 is fastest and produces the least compression,
and 9 is slowest and produces the most compression. 0 is no compression
at all. The default is 9.
The mtime argument is an optional numeric timestamp to be written
to the last modification time field in the stream when compressing.
If omitted or None, the current time is used.'

def __init__(self, filename=None, mode=None, compresslevel=9, fileobj=None, mtime=None):

    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.startswith('r'):
        self.mode = READ
        raw = _GzipReader(fileobj)
        self._buffer = io.BufferedReader(raw)
        self.name = filename
    elif mode.startswith(('w', 'a', 'x')):
        self.mode = WRITE
        self._init_write(filename)
        self.compress = zlib.compressobj(compresslevel, zlib.DEFLATED, (- zlib.MAX_WBITS), zlib.DEF_MEM_LEVEL, 0)
        self._write_mtime = mtime
    else:
        raise ValueError('Invalid    mode:    {!r}'.format(mode))
    self.fileobj = fileobj
    if (self.mode == WRITE):
        self._write_gzip_header()
