1 print('练习:请使用迭代查找一个list中最小和最大值，并返回一个tuple：')
 2 def findMinAndMax(L):
 3     if L !=[]:
 4         (min,max)=(L[0],L[0])
 5         for x in L:
 6             if max<x:
 7                 max=x
 8             if min>x:
 9                 min=x
10         return(min,max)
11     else:
12         return(None,None)
13 
14 
15 
16 
17 if findMinAndMax([]) != (None, None):
18     print('测试失败!')
19 elif findMinAndMax([7]) != (7, 7):
20     print('测试失败!')
21 elif findMinAndMax([7, 1]) != (1, 7):
22     print('测试失败!')
23 elif findMinAndMax([7, 1, 3, 9, 5]) != (1, 9):
24     print('测试失败!')
25 else:
26     print('测试成功!')