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day7.条件和循环

一.if语句

  单分支,单重条件判断

    if expression:
        expr_true_suite
 
  单分支,多重条件判断
    if not  active or over_time >= 10:
        print(‘Warning:service is dead‘)
        warn_tag+=1
 
  if+else
    if expression:
        expr_true_suite
    else:
        expr_false_suite
 
  多分支if+elif+else
    if expession1:
        expr1_true_suite
    elif expression2:
        expr2_true_suite
    elif expession3:
        expr3_true_suite
    else:
        none_of_the_above_suite
 

  三元表达式

    语法:

    expr_true_suite if expession else expr_false_suite

    案例一:

>>> active=1
>>> print(‘service is active‘) if active else print(‘service is inactive‘)
service is active

    案例二:

>>> x=1
>>> y=2
>>> smaller=x if x < y else y
>>> smaller
1

二.while语句

  

2.2.1:基本语法

while expression:

    suite_to_repeat

注解:重复执行suite_to_repeat,直到expression不再为真

 

2.2.2:计数循环

count=0
while (count < 9):
    print(‘the loop is %s‘ %count)
    count+=1 

2.2.3:无限循环

count=0
while True:
    print(‘the loop is %s‘ %count)
    count+=1

技术分享
tag=True
count=0
while tag:
    if count == 9:
        tag=False
    print(the loop is %s %count)
    count+=1 
跳出无限循环

2.2.4:while与break,continue,else连用

技术分享
count=0
while (count < 9):
    count+=1
    if count == 3:
        print(跳出本层循环,即彻底终结这一个/层while循环)
        break
    print(the loop is %s %count)
break跳出本层循环
技术分享
count=0
while (count < 9):
    count+=1
    if count == 3:
        print(跳出本次循环,即这一次循环continue之后的代码不再执行,进入下一次循环)
        continue
    print(the loop is %s %count)
continue跳出本次循环
技术分享
count=0
while (count < 9):
    count+=1
    if count == 3:
        print(跳出本次循环,即这一次循环continue之后的代码不再执行,进入下一次循环)
        continue
    print(the loop is %s %count)
else:
    print(循环不被break打断,即正常结束,就会执行else后代码块)




count=0
while (count < 9):
    count+=1
    if count == 3:
        print(跳出本次循环,即这一次循环continue之后的代码不再执行,进入下一次循环)
        break
    print(the loop is %s %count)
else:
    print(循环被break打断,即非正常结束,就不会执行else后代码块)
循环被break打断,即非正常结束,就不会执行else后代码块

 

2.2.5:while语句小结

  • 条件为真就重复执行代码,直到条件不再为真,而if是条件为真,只执行一次代码就结束了
  • while有计数循环和无限循环两种,无限循环可以用于某一服务的主程序一直处于等待被连接的状态
  • break代表跳出本层循环,continue代表跳出本次循环
  • while循环在没有被break打断的情况下结束,会执行else后代码

 

day7.条件和循环