LIst也可以通过,为什么要有set的存在?
months = ('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul','Aug','Sep','Oct','Nov','Dec') x1 = 'Feb' x2 = 'Sun' if x1 in months: print 'x1: ok' else: print 'x1: error' if x2 in months: print 'x2: ok' else: print 'x2: error' LIst也可以通过,为什么要有set的存在?