一、 初识Python-HelloWorld
1 #!/usr/bin/env python 2 # 当py文件为可执行程序时,需添加该项 3 4 5 # coding: utf-8 6 7 print("Hello World!")
二、 常量和变量
2.1 变量
变量来源于数学,是计算机语言中能储存计算结果或能表示值抽象概念。变量可以通过变量名访问。在指令式语言中,变量通常是可变的。
name = "George"
上述代码声明了一个变量,变量名为: name,变量name的值为:"George"
变量的作用:昵称,其代指内存里某个地址中保存的内容。
变量定义的规则:
1)变量名只能是 字母、数字或下划线的任意组合;
2)变量名的第一个字符不能是数字;
3)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']
拓展:
1. 当一个变量创建后,那么相应的内存地址也就分配完成。
name1 = "george" print(id(name1))
##输出:1978270364536
2. 当修改该变量的值时,变量将会指向一个新的内存地址。
name1 = "john" print(id(name1)) ##输出:1978270364704
3. 当再次创建一个含有相同值得变量时,变量2将指向相同的内存地址
name1 = “george” print(id(name1)) ##输出:1978270364536 name2 = "george" print(id(name2)) ##输出:1978270364536
延伸讨论:
name = "George Guo" print ('Hello, ', name) name_2 = name print ('Hello, ', name_2) name = "Laura Li" print ('Hello, ', name) print ('Hello, ', name_2) # name_2仍保持原来的内存地址,所以输出结果: # Hello, Laura Li ,name # Hello, George Guo ,name2
2.2 常量
“常量”的广义概念是:‘不变化的量’(例如:在计算机程序运行时,不会被程序修改的量)。
# 大写表示常量 PIE = 3.14
三、 用户交互
name = input("username: ") password = input("password: ") print(name, password)
输出:
四、格式化输出
# name = input('namename: ') age = input('age: ') job = input('Job:') #格式化输出:方式一 info1 = """ --------------format info 1------------------------- --------------info1 of """ + name + """ --------------- Name: """+ name + """ Age: """+ age print(info1) #格式化输出:方式二 info2 = """ --------------format info 1------------------------- --------------info2 of %s ----------------------- Name: %s Age: %d """ %(name, name, int(age)) print(info2) #格式化输出:方式三 info3 = """ --------------info3 of {_name} --------------- Name: {_name} Age: {_age} Job: {_job} """.format(_name = name, _age = age, _job= job) print(info3) #格式化输出:方式四 info4 = """ --------------info4 of {0} --------------- Name: {0} Age: {1} Job: {2} """.format(name, age, job) print(info4)
输出:
五、 条件语句
import getpass _username = 'john' _passwd = '123' username = input('username: ') passwd = input('password: ') #passwd = getpass.getpass('password: ') #密文输入 if username == _username and passwd == _passwd: print ('Welcome user {name} login...'.format(name=username)) else: print ('Invalid username or password!')
输出:
六、 循环
#while循环 age_of_oldboy = 56 count = 0 ''' while count<3: guess_age = int(input("Guess age:")) if guess_age ==age_of_oldboy: print ("Yes, you got it!") break elif guess_age > age_of_oldboy: print ("think smaller...") else: print ("think bigger...") count += 1 else: print("You have tried too many times!") #for循环 for i in range(3): guess_age = int(input("Guess age:")) if guess_age ==age_of_oldboy: print ("Yes, you got it!") break elif guess_age > age_of_oldboy: print ("think smaller...") else: print ("think bigger...") else: print("You have tried too many times!") ''' flag = True while flag: for i in range(3): guess_age = int(input("Guess age:")) if guess_age ==age_of_oldboy: print ("Yes, you got it!") break elif guess_age > age_of_oldboy: print ("think smaller...") else: print ("think bigger...") else: print("You have tried too many times!") e = input('To be contine: (type "exit" to exit)') if e == 'exit': flag = False