"Python entry to proficiency" loop statement while loop, for loop

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while is used to "repeatedly execute" a certain piece of code, enter the loop when the "condition is met" , and jump out of the loop when the "condition is not satisfied" .

1. Grammatical format

For different scenarios, while can use different "syntax formats"

1.1、while

The most "basic" grammatical structure, often used in simple scenarios.

while 判断条件：
	执行代码

Example: Define your balance, earn 1 yuan a day, earn enough 20 yuan, you can go to Internet cafes

money = 12

while money < 20:
    print(money, '元：穷逼，离开我的网吧')
    money += 1

print('这位爷，里边儿请')

output:

12 元：穷逼，离开我的网吧
13 元：穷逼，离开我的网吧
14 元：穷逼，离开我的网吧
15 元：穷逼，离开我的网吧
16 元：穷逼，离开我的网吧
17 元：穷逼，离开我的网吧
18 元：穷逼，离开我的网吧
19 元：穷逼，离开我的网吧
这位爷，里边儿请

1.2. Infinite loop

When the judgment condition is always True , the loop will "loop infinitely" . It is often used in some special scenarios, such as heartbeat requests between clients and servers.

while True：
	执行代码

Example: Define your balance, if you don’t earn money every day, if you earn enough 20 yuan, you can go to the Internet cafe.

money = 12

while money < 20:
    print(money, '元：穷逼，离开我的网吧')

print('这位爷，里边儿请')

output:

12 元：穷逼，离开我的网吧
12 元：穷逼，离开我的网吧
	......

1.3 Shorthand form

If the body of the while loop has only "one statement" , it can be written in one line.

money = 12

while money < 20: print(money, '元：穷逼，离开我的网吧')

2. continue skips the loop

The keyword continue can "skip a cycle" , without executing subsequent codes, and directly enter the next cycle.

Example: Define your balance, earn 1 yuan a day, earn enough 20 yuan, you can use the Internet cafe; but earn 15 yuan, you can take a day off.

money = 12

while money < 20:
    money += 1
    if money == 15:
        print('休息一下')
        continue
    print('余额：', money, '继续搬砖')

print('去网吧打游戏')

output:

余额： 13 继续搬砖
余额： 14 继续搬砖
休息一下
余额： 16 继续搬砖
余额： 17 继续搬砖
余额： 18 继续搬砖
余额： 19 继续搬砖
余额： 20 继续搬砖
去网吧打游戏

3. break ends the loop

The keyword break can "end" the entire loop

Example: Define your balance, earn 1 yuan a day, and if you earn 20 yuan, you will go to an Internet cafe; but when you earn 15 yuan, you will be exhausted.

money = 12

while money < 20:
    money += 1
    if money == 15:
        print('啊，我累死了')
        break
    print('余额：', money, '继续搬砖')

print('去网吧打游戏')

output:

余额： 13 继续搬砖
余额： 14 继续搬砖
啊，我累死了
去网吧打游戏

4. for loop

The for loop is often used to "traverse" iterable objects, such as traversing lists, tuples, etc.

Example: iterate through each element in the list

list1 = [1, 2, 3, 4]

for i in list1:
    print(i)

output:

1
2
3
4

5. pass placeholder

The role of the keyword pass is to "occupy space" , do nothing, maintain the integrity of the structure, and avoid "syntax errors" .

For example, as an empty execution body in a loop or a judgment statement:

for i in 'str':
    pass

money = 18
if money > 20:
    pass

Or in the early stage of development, only define the function structure, but do not realize the specific function, first use pass to occupy the place

def function1():
    pass

def funcation2():
    pass

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