python流程控制之if、 while和for 循环

1、if 语句

语法1
  if 条件:
#     代码1
#     ...

# cls='human'
# sex='female'
# age=18
#
# if cls == 'human' and sex == 'female' and age > 16 and age < 22:
#     print('开始表白')
#
# print('end....')
#
#

# 语法2
# if 条件:
#     代码1
#     ...
# else:
#     代码1
#     ...

# cls='human'
# sex='female'
# age=38
#
# if cls == 'human' and sex == 'female' and age > 16 and age < 22:
#     print('开始表白')
# else:
#     print('阿姨好')
#
# print('end....')


# 语法3
# if 条件1:
#     代码1
#     ...
# elif 条件2:
#     代码1
#     ...
# elif 条件3:
#     代码1
#     ...
# ............
# else:
#     代码1
#     ...

'''
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('your score: ') #score='73'
# score=int(score) #score=73
# if score >= 90:
#     print('优秀')
# elif score >= 80:
#     print('良好')
# elif score >= 70:
#     print('普通')
# else:
#     print('很差')


# user_from_db='egon'
# pwd_from_db='123'
#
# user_from_inp=input('username>>>: ')
# pwd_from_inp=input('password>>>: ')
#
# if user_from_inp == user_from_db and pwd_from_inp == pwd_from_db:
#     print('login successfull')
# else:
#     print('user or password error')



#if的嵌套

cls='human'
sex='female'
age=18
is_success=False

if cls == 'human' and sex == 'female' and age > 16 and age < 22:
    print('开始表白...')
    if is_success:
        print('在一起')
    else:
        print('我逗你玩呢....')
else:
    print('阿姨好')

print('end....')

2、while 循环
#while语法,while循环又称为条件循环# while 条件:

#     code3
#     ....


# user_db='egon'
# pwd_db='123'
#
# while True:
#     inp_user=input('username>>: ')
#     inp_pwd=input('password>>: ')
#     if inp_user == user_db and inp_pwd == pwd_db:
#         print('login successfull')
#     else:
#         print('user or password error')


#2 while+break:break的意思是终止掉当前层的循环,.执行其他代码
# while True:
#     print('1')
#     print('2')
#     break
#     print('3')

# user_db='egon'
# pwd_db='123'
# #
# while True:
#     inp_user=input('username>>: ')
#     inp_pwd=input('password>>: ')
#     if inp_user == user_db and inp_pwd == pwd_db:
#         print('login successfull')
#         break
#     else:
#         print('user or password error')


# print('其他代码')

#3 while+continue:continue的意思是终止掉本次循环,.直接进入下一次循环
#ps:记住continue一定不要加到循环体最后一步执行的代码
# count = 0
# while count < 10:
#     count += 1
#     if count == 8:
#         continue
#     print(count)

# while True:
#     if 条件1:
#         code1
#         code2
#         code3
#         continue #无意义
#     elif 条件1:
#         code1
#         continue #有意义
#         code2
#         code3
#     elif 条件1:
#         code1
#         code2
#         code3
#         continue #无意义
#     ....
#     else:
#         code1
#         code2
#         code3
#         continue #无意义


#while循环嵌套
user_db='egon'
pwd_db='123'

while True:
    inp_user=input('username>>: ')
    inp_pwd=input('password>>: ')
    if inp_user == user_db and inp_pwd == pwd_db:
        print('login successfull')
        while True:
            cmd=input('请输入你要执行的命令: ')
            if cmd == 'q':
                break
            print('%s 功能执行...' %cmd)
        break
    else:
        print('user or password error')


print('end....')

#while+tag
user_db='egon'
pwd_db='123'

tag=True
while tag:
    inp_user=input('username>>: ')
    inp_pwd=input('password>>: ')
    if inp_user == user_db and inp_pwd == pwd_db:
        print('login successfull')
        while tag:
            cmd=input('请输入你要执行的命令: ')
            if cmd == 'q':
                tag=False
            else:
                print('%s 功能执行...' %cmd)

    else:
        print('user or password error')


print('end....')



#while+else (***)
n=1
while n < 5:
    # if n == 3:
    #     break
    print(n)
    n+=1
else:
    print('在整个循环结束后,会进行判断:只有while循环在没有被break结束掉的情况下才会执行else中的代码')

3、for 循环
（1）在列表和字典中取值

# name = ['ggs','qqc','ccf','vvf']
# n = 0      #用while循环加索引的方式取值（比较麻烦）
# while n<len(name):
#     print(name[n])
#     n += 1

# for n in name : #直接用for循环更加便捷
#     print(n)

# x = {'name':'qqc','hobbis':'read','sex':'mlax'}
# for y in x :       #取字典的值，先取键（y),再通过键（y)取值：x[y]
#     print(y,x[y])
name = ['ggs','qqc','ccf','vvf']
# for x in range(len(name)):   #len() 长度
#     print(x,name[x])  #取索引和值

（2）for循环嵌套

# for x in range(5):   #for循环嵌套
#     print('------%s------' %x)
#     for y in range(3):
#         print('%s' %y)

# for + break or continue
# x = ['rrt','hhj','qqc','cch']
# for y in x :
#     if y == 'qqc':
#         continue
#     print(y)

# for + else  在for循环执行完后打印else代码内容，如果for循环中有break,则不打印else代码
# for x in range(5):
#     if x == 3:

# else :
#     print('执行完毕')

python流程控制之if、 while和for 循环

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