import random def genrand(small, big) :     return small + (big-small) * random.random() def display(small, big) :     return r'请输入上下限(默认%.2f~%.2f):' % (small, big) big = 100 small = 0 while True :     try :         s = input(display(small, big)).strip()         if s.lower() == 'exit' :             break         a = s.split()         if a != [] :             big = float(a[1])             small = float(a[0])         rand = genrand(small, big)         print('(%.2f~%.2f): %.3fn' % (small, big, rand))     except :         print('--Error--n')