Python课后练习：迭代

from collections import Iterable

d = {'a': 1, 'b': 2, 'c': 3}
for key in d:
    print(key)
for value in d.values():
    print(value)
for key, value in d.items(): #这是键值对的迭代方式
    print(key, value)

c = ['123', '321', '456']
for i, num in enumerate(c): #list的迭代用内置函数
    print(i, num)

# for i, num in c:
# print(i, num)  #迭代的时候，list没有索引机制，只能访问的时候用索引访问

print(isinstance(c, Iterable))
for x, y in [(1, 1), (2, 4), (3, 9)]:
    print(x, y)

请使用迭代查找一个list中最小和最大值，并返回一个tuple：
def findMinAndMax(L):
    if len(L) == 0:
        return None, None
    min = L[0]
    max = L[0]
    for i in L:
        if i < min:
            min = i
        if i > max:
            max = i
    return min, max


if findMinAndMax([]) != (None, None):
    print('测试失败!')
elif findMinAndMax([7]) != (7, 7):
    print('测试失败!')
elif findMinAndMax([7, 1]) != (1, 7):
    print('测试失败!')
elif findMinAndMax([7, 1, 3, 9, 5]) != (1, 9):
    print('测试失败!')
else:
    print('测试成功!')