def st_join_enumerate(items, sep='SEP', comma=','):
    """
    joins strings using an sequential seperator

    example:
      st_join_enumerate(["a","b","c"])
      'a,SEP1,b,SEP2,c'
    """
    ret = ''
    for a, b in enumerate(items):
        if a == 0:
            ret = b
        else:
            ret += comma + sep + str(a) + comma + b
    return ret
