循环

• 如果要多次做重复的事情,考虑用循环.例如点击下一页,求和等

for循环

基本格式

for 临时变量 in 可迭代对象:
    循环满足条件时执行的代码
else:
    循环不满足条件时执行的代码

练习

#!/usr/bin/env python
# -*- coding:utf-8 -*-
name = "hello world"
for x in name:
    print(x)

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# 起始位置默认为0，到10结束，不包括10
for x in range(10):
    print(x)

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# 起始位置为2，到10结束，不包括10
for x in range(2, 10):
    print(x)
else:
    print("结束了吧")

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# 3表示步长，每次加3，默认每次加1
for x in range(2, 10, 3):
    print(x)
else:
    print("结束了吧")

break

• 结束整个循环

#!/usr/bin/env python
# -*- coding:utf-8 -*-
for x in range(10):
    if x == 5:
        break
    else:
        print(x)

#!/usr/bin/env python
# -*- coding:utf-8 -*-
for x in range(10):
    for y in range(10):
        if x + y == 10:
            print("结束循环")
            # 这个break只跳出y的那个循环，x那个循环没有跳出
            break
        else:
            print(x, y)

continue

• 结束本次循环执行下次循环

#!/usr/bin/env python
# -*- coding:utf-8 -*-
for x in range(10):
    for y in range(10):
        if x + y == 10:
            print("跳过本次循环继续下一次循环")
            continue
        else:
            print(x, y)

补充:break和continue只能用在循环中,只对离自己最近的循环有效

while循环

基本格式

while 条件:
    条件满足时，做的事情1
    条件满足时，做的事情2
    条件满足时，做的事情3
    ...(省略)...

练习

计算1-100的和

#!/usr/bin/env python
# -*- coding:utf-8 -*-

""" 
@author: 张泽楠 
@contact: [email protected] 
@file: main.py 
@time: 2018/3/8 19:42 
"""
count = 1
total_num = 0
while count <= 100:
    total_num = total_num + count
    count = count + 1
print("1-100的总和为{}".format(total_num))

计算n的阶乘

#!/usr/bin/env python
# -*- coding:utf-8 -*-

""" 
@author: 张泽楠 
@contact: [email protected] 
@file: main.py 
@time: 2018/3/8 19:42 
"""
count = 1
total_num = 0
while count <= 10:
    total_num = total_num * count
    count = count + 1
print("10的阶乘为{}".format(total_num))

打印九九乘法表

#!/usr/bin/env python
# -*- coding:utf-8 -*-

""" 
@author: 张泽楠 
@contact: [email protected] 
@file: main.py 
@time: 2018/3/8 19:42 
"""
line1 = 1
while line1 < 10:
    line2 = 1
    print_str = ""
    while line2 <= line1:
        print_str = print_str + "{} * {} = {}  ".format(line2, line1, line1*line2)
        line2 = line2 + 1
    print(print_str)
    line1 = line1 + 1

补充

• for循环能做的都能用while循环实现
• while循环能做的for循环不一定能实现
• for循环注重循环次数
• while循环注重循环条件