How to use the maxminddb.extension.Reader function in maxminddb

* MODE_MMAP_EXT - use the C extension with memory map.
            * MODE_MMAP - read from memory map. Pure Python.
            * MODE_FILE - read database as standard file. Pure Python.
            * MODE_MEMORY - load database into memory. Pure Python.
            * MODE_FD - the param passed via database is a file descriptor, not
                        a path. This mode implies MODE_MEMORY.
            * MODE_AUTO - tries MODE_MMAP_EXT, MODE_MMAP, MODE_FILE in that
                          order. Default mode.
    """
    has_extension = maxminddb.extension and hasattr(maxminddb.extension, "Reader")
    if (mode == MODE_AUTO and has_extension) or mode == MODE_MMAP_EXT:
        if not has_extension:
            raise ValueError(
                "MODE_MMAP_EXT requires the maxminddb.extension module to be available"
            )
        return maxminddb.extension.Reader(database)
    if mode in (MODE_AUTO, MODE_MMAP, MODE_FILE, MODE_MEMORY, MODE_FD):
        return PyReader(database, mode)
    raise ValueError("Unsupported open mode: {0}".format(mode))

* MODE_MMAP - read from memory map. Pure Python.
            * MODE_FILE - read database as standard file. Pure Python.
            * MODE_MEMORY - load database into memory. Pure Python.
            * MODE_FD - the param passed via database is a file descriptor, not
                        a path. This mode implies MODE_MEMORY.
            * MODE_AUTO - tries MODE_MMAP_EXT, MODE_MMAP, MODE_FILE in that
                          order. Default mode.
    """
    has_extension = maxminddb.extension and hasattr(maxminddb.extension,
                                                    'Reader')
    if (mode == MODE_AUTO and has_extension) or mode == MODE_MMAP_EXT:
        if not has_extension:
            raise ValueError(
                "MODE_MMAP_EXT requires the maxminddb.extension module to be available"
            )
        return maxminddb.extension.Reader(database)
    elif mode in (MODE_AUTO, MODE_MMAP, MODE_FILE, MODE_MEMORY, MODE_FD):
        return maxminddb.reader.Reader(database, mode)
    raise ValueError('Unsupported open mode: {0}'.format(mode))