Python学习--day4

day4

一、常量

　　Python并未提供如C/C++/Java一样的const修饰符，换言之，python中没有常量，python程序一般通过约定俗成的变量名全大写的形式表示这是一个常量。

AGE = 78          #变量名全大写
print(AGE)

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 二、流程控制：

　　1、流程控制之if判断：

'''语法1：
if 条件:
    代码1
    代码2
    代码3
    ...
'''
# age_of_bk=30
# print('start.....')
#
# inp_age=input('>>>: ') #inp_age='18'
# inp_age=int(inp_age)
# if inp_age == age_of_bk:
#     print('猜对了')
#
# print('end.....')
'''语法2：
if 条件:
    代码1
    代码2
    代码3
    ...
else：
    代码1
    代码2
    代码3
    ...
'''
# age=38
# gender='male'
# is_beautiful=True
#
# if age >= 18 and age <= 25 and gender == 'female' and is_beautiful:
#     print('开始表白。。。。')
#
# else:
#     print('阿姨好')
#
语法3：
if 条件1:
    代码1
    代码2
    代码3
    ...
elif 条件4:
    代码1
    代码2
    代码3
    ...
else:
    代码1
    代码2
    代码3
    ...
'''
# score=input('your score>>: ')
# 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')
'''
语法4：
if 条件1:
    if 条件2:
        代码1
        代码2
        代码3
        ...
    代码2
    代码3

'''
# age=18
# gender='female'
# is_beautiful=True
# is_successful=True
# 
# if age >= 18 and age <= 25 and gender == 'female' and is_beautiful:
#     print('开始表白。。。。')
#     if is_successful:
#         print('在一起')
#     else:
#         print('我逗你玩呢。。。')
# else:
#     print('阿姨好')

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　　2、流程控制之while循环：

#1. while循环：条件循环
# I: 基本语法
# while 条件:
#     代码1
#     代码2
#     代码3
#     ...

# 示范
# name_of_bk='egon'
# pwd_of_bk='123'
#
# tag=True
# while tag:
#     inp_name=input('your name>>: ')
#     inp_pwd=input('your password>>: ')
#     if inp_name == name_of_bk and inp_pwd == pwd_of_bk:
#         print('login successful')
#         tag=False
#     else:
#         print('username or password error')
#
#     print('other code...')

# II: while+break:break代表结束本层循环
# 示范：
# while True:
#     print(1)
#     break
#     print(2)
#     print(3)

# name_of_bk='egon'
# pwd_of_bk='123'
#
# while True:
#     inp_name=input('your name>>: ')
#     inp_pwd=input('your password>>: ')
#     if inp_name == name_of_bk and inp_pwd == pwd_of_bk:
#         print('login successful')
#         break
#     else:
#         print('username or password error')
#
#     print('other code......')


# III: while + continue: continue代表结束本次循环，直接进入下一次
# 示范
# count=1
# while count < 6:
#     if count == 3:
#         count+=1
#         continue
#     print(count)
#     count+=1


# 输错三次退出
# name_of_bk='egon'
# pwd_of_bk='123'
#
# count=0
# while True:
#     if count == 3:
#         print('输错的次数过多。。。')
#         break
#     inp_name=input('your name>>: ')
#     inp_pwd=input('your password>>: ')
#     if inp_name == name_of_bk and inp_pwd == pwd_of_bk:
#         print('login successful')
#         break
#     else:
#         print('username or password error')
#         count+=1 #count=3 输错3次


# IV:while + else
# count=0
# while True:
#     if count == 10:
#         break
#     print(count)
#     count+=1
#
# else:
#     print("else的子代块只有在while循环没有被break打断的情况下才会执行")



# count=0
# while count <= 10:
#     print(count)
#     count+=1
#
# else:
#     print("else的子代块只有在while循环没有被break打断的情况下才会执行")

# name_of_bk='egon'
# pwd_of_bk='123'
# 
# count=0
# tag=True
# while tag:
#     if count == 3:
#         print('输错的次数过多。。。')
#         break
#     inp_name=input('your name>>: ')
#     inp_pwd=input('your password>>: ')
#     if inp_name == name_of_bk and inp_pwd == pwd_of_bk:
#         print('login successful')
#         while tag:
#             print("""
#             0 退出
#             1 购物
#             2 支付
#             3 查看购物
#             """)
#             cmd=input('>>>: ')
#             if cmd == '0':
#                 tag=False
#                 continue
#             if cmd == '1':
#                 print('购物。。。。。。。')
#             elif cmd == '2':
#                 print('支付。。。。。')
#             elif cmd == '3':
#                 print('查看购物车')
#             else:
#                 print('输入错误的指令')
#     else:
#         print('username or password error')
#         count+=1 #count=3 输错3次

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