和我一起学python，控制语句（life is short ,we need python）

迷南。 2022-03-29 06:45 157阅读 0赞

**控制语句**

if/elif/else

if语句和一般编程语言一样，条件为true 执行

如： if true :

print 'true'         <----if、else下对齐，要使用相同的空格或者tab

else:

print 'false'

但是，python有自己的特点:

1. if else 要求严格分层对齐 对于嵌套if、else语句都应当严格分层对齐。

2.if else 关键字后边一定要加冒号 ：

#!/usr/bin/python
    '''
    create By to be crazy
    All rights Reserved
    
    '''
    score=int(raw_input("Enter your score please\n"))
    if (score>0 and score<100 ):
            if(score>90):
              print "your score is A"
            elif(score>60):
              print "your score is B"
            else:
              print "your score is C"
    else:
            print "your score is not correct"

可以看出，if嵌套如何匹配else的，第一层if使用一个tab对齐，第二层使用一个空格对齐，切记elif

**循环结构　**

while/for

for 适用于list和dictionary的遍历，也可以是字符串遍历

word = "Programming is fun!"
    
    for letter in word:
        # Only print out the letter i
        if letter == "i":
            print letter

for item in [1, 3, 21]: 
        print item

webster = {
        "Aardvark" : "A star of a popular children's cartoon show.",
        "Baa" : "The sound a goat makes.",
        "Carpet": "Goes on the floor.",
        "Dab": "A small amount."
    }
    
    # Add your code below!
    for key in webster:
        print webster[key]

for 可以配合range()使用

for i in range(10):
        print i

print 0~9

for loop 遍历dictionary

d = {
        'x': 9, 'y': 10, 'z': 20}
    for key in d:
        if d[key] == 10
            print "This dictionary has the value 10!"

while 循环

先检查condition是否为true，为ture就继续循环

loop_condition = True
    
    while loop_condition:
        print "I am a loop"
        loop_condition = False

**`while`/`else `**

** while/else 不同于if/else 当循环的条件为False，else语句块会被执行也就是循环从未被执行或在循环正常结束时，都会执行else，如果循环被中断,return、break了，则不执行else。**

import random
    
    print "Lucky Numbers! 3 numbers will be generated."
    print "If one of them is a '5', you lose!"
    
    count = 0
    while count < 3:
        num = random.randint(1, 6)
        print num
        if num == 5:
            print "Sorry, you lose!"
            break
        count += 1
    else:
        print "You win!"

当执行到break，就不执行else

若循环正常结束，执行else

需要注意：不要忘记for和while语句的冒号

break/continue

break 跳出循环

count = 0
    
    while True:
        print count
        count += 1
        if count >= 10:
            break #exit the current loop.