def get_offset(attrs):
    """
    Extract offset from the given attributes.

    :param attrs: The string of a compound variable fields split by tabs.
      If an offset is given, it must go the first element.
    :return: The value of offset if given or 0.
    """
    offset = 0
    if attrs is not None:
        try:
            offset = int(attrs.split('\t')[0])
        except ValueError:
            pass
    return offset