def unpack_archive(filename, extract_dir=None, format=None):
    if extract_dir is None:
        extract_dir = os.getcwd()

    if format is not None:
        try:
            format_info = _UNPACK_FORMATS[format]
        except KeyError:
            raise ValueError("Unknown unpack format '{0}'".format(format))

        func = format_info[1]
        func(filename, extract_dir, **dict(format_info[2]))
    else:
        # we need to look at the registered unpackers supported extensions
        format = _find_unpack_format(filename)
        if format is None:
            raise ReadError("Unknown archive format '{0}'".format(filename))

        func = _UNPACK_FORMATS[format][1]
        kwargs = dict(_UNPACK_FORMATS[format][2])
        func(filename, extract_dir, **kwargs)
Add a value in the memcached server iff it doesn't already exist.
dataset/ETHPy150Open GeekTrainer/Flask/Work/Trivia - Module 5/env/Lib/site-packages/pip/_vendor/distlib/_backport/shutil.py/unpack_archive--crossover with--dataset/ETHPy150Open dustin/memcached-test/mc_bin_client.py/MemcachedClient.add