流程控制

一if循环

   1. if判断

sex = 'female'
age = 20
weight = 50
if age > 18 and age < 22 and sex == 'female' and weight == 50:
    print('你好')

  2.if+else 

sex = 'female'
age = 20
weight = 50
if age > 18 and age < 22 and sex == 'female' and weight == 50:
    print('你好')
else:
    print('再见')

   3..if嵌套

sex = 'female'
age = 20
weight = 50
is_successful=True
if age > 18 and age < 22 and sex == 'female' 
        and weight == 50:
    print('你好')
    if is_successful:
        print('了解一下')
    else:
        print('什么爱情')
else:
    print('再见')

   4.if+elif

如果：成绩>=90，那么：优秀

       如果成绩>=80且<90,那么：良好

       如果成绩>=70且<80,那么：普通

       其他情况：很差
 score = input('请输入你的分数：')
 score = int(score)
 if score >= 90:
     print('优秀')
 elif score >= 80:
     print('良好')
 elif score >= 70:
     print('普通')
 else:
     print('很差')

二while

while循环由又之为while条件循环

while True:
    name = input('please input you name：')
    pwd = input('please input you password：')
    if name == 'egon' and pwd == '123':
        print(' login successful')
    else:
        print('name or password error')

while条件改变

tag = True
while tag:
    name = input('please input you name:')
    pwd = input('please input you password:')
    if name == 'egon' and pwd == '123':
        print('login succesful')
        tag = False
    else:
        print('name or password error')
    print('=====>')

while+break

退出本层(结束整个)循环

while True:
    name = input('please input you name:')
    pwd = input('please input you password:')
    if name == 'egon' and pwd == '123':
        print('login succesful')
        break
    else:
        print('name or password error')
    print('=====>')

while+continue

退出本次(单次)循环

while count<6:
    if count==4:
        count+=1
        continue
    print(count)
    count+=1

while+else

当while 循环正常执行完，中间没有被break 中止的话，就会执行else后面的语句
count = 0
while count <= 5 :
    count += 1
    print("Loop",count)

else:
    print("循环正常执行完啦")
print("-----out of while loop ------")
输出
Loop 1
Loop 2
Loop 3
Loop 4
Loop 5
Loop 6
循环正常执行完啦
-----out of while loop ------

#如果执行过程中被break啦，就不会执行else的语句啦
count = 0
while count <= 5 :
    count += 1
    if count == 3:break
    print("Loop",count)

else:
    print("循环正常执行完啦")
print("-----out of while loop ------")
输出

Loop 1
Loop 2
-----out of while loop ------

三for循环

1 迭代式循环：for，语法如下

　　for i in range(10):

　　　　缩进的代码块

2 break与continue（同上）

3 循环嵌套

for i in range(1,3):
    for j in range(1,4):
        print(i,j)

1 1
1 2
1 3
2 1
2 2
2 3

for i in range(1,10):
    for j in range(1,i+1):
        print('%s*%s=%s' %(j,i,i*j),end=' ')
    print()


1*1=1 
1*2=2 2*2=4 
1*3=3 2*3=6 3*3=9 
1*4=4 2*4=8 3*4=12 4*4=16 
1*5=5 2*5=10 3*5=15 4*5=20 5*5=25 
1*6=6 2*6=12 3*6=18 4*6=24 5*6=30 6*6=36 
1*7=7 2*7=14 3*7=21 4*7=28 5*7=35 6*7=42 7*7=49 
1*8=8 2*8=16 3*8=24 4*8=32 5*8=40 6*8=48 7*8=56 8*8=64 
1*9=9 2*9=18 3*9=27 4*9=36 5*9=45 6*9=54 7*9=63 8*9=72 9*9=81 

4 range():

for i in range(10):
    print(i)

0
1
2
3
4
5
6
7
8
9

 注意： 　　python2中:range(1,5)直接生成[1,2,3,4]列表 　　

                    python3中：range(1,5)不会直接生成列表，依旧是 range(1,5)