python 流程控制

1 判断 if

2 条件循环 while

3 for迭代式循环

4 break和continue关键字

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3.1 判断 if

#第一种：
age=28
 if age > 18:
     print('表白')

#第二种if...else...：
if age > 18 and age < 22:
    print('表白')
else:
      print('阿姨好')

#第三种 #if多分支：
score=input('>>: ')
score=int(score)
if score >= 90:
    print('优秀')
elif score >= 80:
    print('良好')
elif score >= 60:
    print('合格')
else:
print('滚犊子')

if嵌套： 

age=19
is_pretty=True
success=True
if age > 18 and age < 22 and is_pretty:
    if success:
        print('表白成功，在一起')
    else:
        print('去他妈的爱情')
else:
    print('阿姨好')

3.2 条件循环 while

3.2.1 格式一：while：条件循环

while 条件:

循环体

count=0
while count <= 10:
    print(count)
count+=1

 嵌套循环

count = 1
while True:
    if count > 3:
         print('too many tries')
         break
     name = input('name>>: ')
     password = input('password>>: ')
     if name == 'egon' and password == '123':
         print('login successfull')
         while True:
             cmd=input('cmd>>: ') #q
             if cmd == 'q':
                 break
             print('run %s' %cmd)
         break
     else:
         print('user or password err')
         count += 1

使用tag

 count = 1
 tag=True
 while tag:
     if count > 3:
         print('too many tries')
         break
     name = input('name>>: ')
     password = input('password>>: ')
     if name == 'egon' and password == '123':
         print('login successfull')
         while tag:
             cmd=input('cmd>>: ') #q
             if cmd == 'q':
                 tag=False
                 continue
             print('run %s' %cmd)
     else:
         print('user or password err')
         count += 1

3.2.2 格式二：while+else

count=0
while count <= 5:
    if count == 3:
        break
    print(count)
    count+=1
else:
print('当while循环在运行过程中没有被break打断，则执行我')

3.3 for迭代式循环

3.3.1 格式一：

for i in range(1,10,2):
print(i)

l1=['a','b','c','d','e']
for i in range(len(l1)):
    print(i,l1[i])

3.3.2 格式二：for+else:

for i in range(5):
if i == 3:break
    print(i)
else:
    print('当循环在运行过程中没有被break打断，则执行我')

3.4 break和continue关键字

while+break

count=0
while True:
     if count == 5:
         break   #跳出本层循环
     print(count)
     count+=1

while+continue

#1,2,3,4,5,7
count=1
while count <= 7:
    if count == 6:
        count += 1
        continue  #跳出本次循环
    print(count)
    count+=1