def parse_limits(limits):
    if not limits:
        return [None, None]
    
    limits = limits.strip()

    if limits[0] == '-':
        return [None, int(limits[1:])]
    elif limits[-1] == '-':
        return [int(limits[:-1]), None]
    
    limits = limits.split("-")

    if len(limits) != 2:
        print("unknown limits: " + str(limits) + " - using no limits")
        return [None, None]
    
    try:
        return [int(x) for x in limits]
    except ValueError as exp:
        print(exp + " - using no limits")
        return [None, None]