Python学习笔记——day1

Posted 2020-11-06 byho

#Python day1

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[TOC] ##1.Hellow World程序 ###1）Hellow World 在linux里创建一个叫hellow.py的文件。

文件内容：

#!/usr/bin/env python
print("Hellow World！")

在linux中需要指定解释器#!/usr/bin/env python 意思是到整个linux系统中找名为python的环境变量。

给予文件执行权限，使用./hellow.py执行文件。

输出结果：

Hellow World！

Python常用转义符:

转义字符|具体描述 ---|--- \n|换行 \r|回车 \v|纵向制表符 \t|横向制表符 \" | " \\ |
\(在行尾时)|续行符 \a|响铃 \b|退格（Backspace） \000|空

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##2.变量 ###1)什么是变量？

变量用于存储在计算机程序中引用和操作的信息。它们还提供了一种用描述性名称标记数据的方法，这样我们的程序就能更清晰地被读者和我们自己理解。将变量看作保存信息的容器是很有帮助的。它们的唯一目的是在内存中标记和存储数据。然后可以在整个程序中使用这些数据。

###变量定义的规则：

• 变量定义的规则
  • 变量名只能是字母、数字或下划线的任意组合
  • 变量名的第一个字符不能是数字
  • 写的变量名要有含义，否则自己和别人都看不懂
  • 变量名最好不要是中文或拼音，多个单词用下划线分隔
  • 以下关键字不能声明为变量名

[‘and‘, ‘as‘, ‘assert‘, ‘break‘, ‘class‘, ‘continue‘, ‘def‘, ‘del‘, ‘elif‘, ‘else‘, ‘except‘, ‘exec‘, ‘finally‘, ‘for‘, ‘from‘, ‘global‘, ‘if‘, ‘import‘, ‘in‘, ‘is‘, ‘lambda‘, ‘not‘, ‘or‘, ‘pass‘, ‘print‘, ‘raise‘, ‘return‘, ‘try‘, ‘while‘, ‘with‘, ‘yield‘]

###什么是常量？

常量：定义后，不会变的量，比如π是3.14...

python定义常量，变量名要大写比如：PIE = "em"

###2)变量的赋值：

name = "byh"
name2 = name

print(name,"-----",name2)

name = "em"
print(name,"-----",name2)

print:输出字符

输出结果：

byh ----- byh
em ----- byh

Process finished with exit code 0

###为什么第二个name2输出的是 byh,而不是em呢？

• 因为：
  • name2只是通过name找到byh的，name2≠name
  • name = em只是从新定义了name，name2还是通过第一个name变量找到byh

###注释:

当行注释	“#”标识当行
多行注释	‘‘‘ 或 """ 都表示多行注释

###3)三元运算

a = 1
b = 5
c = 9

d = a if a > b else c
print(d)

d = a if a < b else c
print(d)

输出结果：

9        #如果a > b条件不成立，结果就是c的值
1        #如果a < b条件成立,结果就是a的值

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##3.用户输入 ###1)简单用户输入

username = input("username:")
password = input("password:")

print("Hellow",username)

输入密码时，如果要密码不可见，需要使用getpass模块中的getpass方法：

import getpass

username = input("username:")
password = getpass.getpass("password:")

print("Hellow",username)

###2)用户输入，输出调用变量

方法一：

name = input("name:")
age = int(input("age:"))
print(type(age))
job = input("job:")
salary = int(input("salary:"))
print(type(salary))

info = ‘‘‘
-------- info of %s--------
Name:%s
Age:%d
Job:%s
Salary:%d
‘‘‘ %(name,name,age,job,salary)

print(info)

%s	代表string字符串
%d	代表整数
%f	代表有小数点的数
int()	强制转换类型为integer
str()	强制转换类型为string
print(type(salary))	输出字符串类型

输出结果：

name:em
age:19
<class ‘int‘>
job:IT
salary:1234567
<class ‘int‘>

-------- info of em--------
Name:em
Age:19
Job:IT
Salary:1234567


Process finished with exit code 0

>方法二： ``` #Author:byh name = input("name:") age = int(input("age:")) print(type(age)) job = input("job:") salary = int(input("salary:")) print(type(salary))

info = ‘‘‘ -------- info of -------- Name: Age: Job: Salary: ‘‘‘ .format(_name=name, _age=age, _job=job, _salary=salary)

print(info)

>输出结果：

name:em age:19 <class ‘int‘> job:IT salary:1234567 <class ‘int‘>

-------- info of em-------- Name:em Age:19 Job:IT Salary:1234567

Process finished with exit code 0

<br/>

>方法三：

#Author:byh name = input("name:") age = int(input("age:")) print(type(age)) job = input("job:") salary = int(input("salary:")) print(type(salary))

info = ‘‘‘ -------- info of {0}-------- Name:{0} Age:{1} Job:{2} Salary:{0} ‘‘‘ .format(name,name,age,job,salary)

print(info)

>输出结果：

name:em age:19 <class ‘int‘> job:IT salary:1234567 <class ‘int‘>

-------- info of em-------- Name:em Age:em Job:19 Salary:em

Process finished with exit code 0

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##4.表达式if ... else
###场景一 : 用户登陆验证

_username = "byh" _password = "123" username = input("username:") password = input("password:")

if _username == username and _password == password: print("Welcome user login...".format(name=_username)) else: print("Invaild username or password!")

elif|如果这个条件不成立，那么下个条件是否成立呢
---|---

>输出结果：

#验证成功输出 username:byh password:123 Welcome user byh login...

#验证失败输出 username:em password:123 Invalid username or password!

###场景二 : 猜年龄游戏

_myage = 22 myage = int(input("myage:"))

if myage == _myage: print("yes, it is") elif myage > _myage: print("should be smaller..") else: print("should be more big..")

>输出结果

myage:17 should be more big..

myage:23 should be smaller..

myage:22 yes, it is

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##5.while循环
###1)简单while循环

count = 0 while True: print("count:",count) count +=1 if count == 1000: break

>当这个条件成立时：True（永远为真），如果没有定义 `break`条件结束循环，则会一会循环下去。

<br/>

###2)while循环猜年龄游戏

#实现用户可以不断的猜年龄，最多3次机会，继续按如意键，退出按“n”

_myage = 22 count = 0

while count < 3: myage = int(input("myage:")) if myage == _myage: print("yes it is.") break elif myage > _myage: print("should be smaller...") else: print("should be more big...") count +=1 if count == 3: countine_config = input("do you want to keep gussing?") if countine_config !="n": count = 0

break|结束当前整个循序
---|---
continue|跳出本次循环，进入下次循环
count|添加计数


>输出结果：

#继续猜： myage:1 should be more big... myage:2 should be more big... myage:3 should be more big... do you want to keep gussing? myage:12 should be more big... myage:22 yes it is.

Process finished with exit code 0

#不猜退出： myage:1 should be more big... myage:2 should be more big... myage:3 should be more big... do you want to keep gussing?n

Process finished with exit code 0

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##6.for循环
###1）简单for循环

#0,10是范围，1是增数 for i in range(0,10,1): print("number",i)

>输出结果：

number 0 number 1 number 2 number 3 number 4 number 5 number 6 number 7 number 8 number 9

Process finished with exit code 0

###2)for循环猜年龄游戏

#用户最多猜3次 _myage = 22

for i in range(3): myage = int(input("myage:")) if myage == _myage: print("yes it is.") break elif myage > _myage: print("should be smaller..") else: print("should be more big..")

else: print("you have tried too many times")

>输出结果：

myage:1 should be more big.. myage:2 should be more big.. myage:3 should be more big.. you have tried too many times

Process finished with exit code 0

##7.作业
###1）作业三：多级菜单
* 三级菜单
* 可一次选择进入各子菜单
* 使用知识点：列表、字典

#Author:byh #定义三级字典 data = { ‘北京‘:{ "昌平":{ "沙河":["oldboy","test"], "天通苑":["宜家","大润发"], }, "朝阳":, "海淀":, }, ‘山东‘:{ "德州":, "青岛":, "济南":, }, ‘广东‘:{ "东莞":, "广州":, "佛山":, }, } exit_flag = False

while not exit_flag: for i in data: #打印第一层 print(i)

choice = input("选择进入1:")
if choice in data:  #判断输入的层在不在
    while not exit_flag:
        for i2 in data[choice]:  #打印第二层
            print(i2)

        choice2 = input("选择进入2:")
        if choice2 in data[choice]:     #判断输入的层在不在
            while not exit_flag:
                for i3 in data[choice][choice2]:    #打印第三层
                    print(i3)

                choice3 = input("选择进入3:")
                if choice3 in data[choice][choice2]:    #判断输入的层在不在
                    for i4 in data[choice][choice2][choice3]:   #打印最后一层
                        print(i4)

                    choice4 = input("最后一层，按b返回:")
                    if choice4 == "b":  #返回
                        pass  #占位符，或以后可能添加代码
                    elif choice4 == "q":    #退出
                        exit_flag = True
                if choice3 == "b":
                    break
                elif choice3 == "q":
                    exit_flag = True
        if choice2 == "b":
            break
        elif choice2 == "q":
            exit_flag = True