python—变量和简单数据类型

1、变量

在程序中可随时修改变量的值，python始终记录变量的最新值

变量名：必须以字母或者下划线开头，只能包含字母数字和下划线，建议使用下划线+小写字母的方式命名，不能为函数名和python关键字

message = "one"
print(message)

message = "two"
print(message)

　输出：

one
two

2、字符串

name = "hello world, I AM HAPPY hAhAhAHAha"
print(name.title())   #每个单词首字母大写
print(name.upper())   #全部转成大写
print(name.lower())   #全部转成小写

　输出：

Hello World, I Am Happy Hahahahaha
HELLO WORLD, I AM HAPPY HAHAHAHAHA
hello world, i am happy hahahahaha

first_name = "jim"
second_name = "green"
full_name = first_name + " " + second_name
message = "Hello, " + full_name.title() + "!"   #字符串的拼接
print(message)

　输出：

Hello, Jim Green!

print("Languages:\n\tPython\n\tC\n\tJava")

输出：

Languages:
        Python
        C
        Java

favorite_language = "   Python   "
print("before: ", favorite_language)
print(favorite_language.lstrip())    #删除左边空格
print(favorite_language.rstrip())    #删除右边空格
print(favorite_language.strip())     #删除两边空格
print("after: ", favorite_language);

输出：

before: Python
Python
Python
Python
after: Python

message = "hello, I'm crazybird123..."
print(message)

输出：hello, I'm crazybird123...

message = 'hello, I am "crazybird123"!'  #单引号里面用双引号输出"crazybird123"

 print(message)

输出：

hello, I am "crazybird123"!

　

3、数字

print(  **  ) #2的5次方
print(  +  *  )
print( ( + ) *  )
print(0.1 + 0.2)   #浮点数小数位不确定

输出：

32
14
20
0.30000000000000004

age =
message = "Happy " + str(age) + "rd Birthday!"   #str（）将非字符串类型转换成字符串
print(message)

输出：Happy 25rd Birthday!

height = 180.009
message = "He is " + str(height) + " meters!"
print(message)

输出：He is 180.009 meters!

整数除法：python2和python有区别

python3中：print(3/2) 输出是1.5      而在pyuthon2中输出确实1。而在python3中使用//表示floor除法，即3//2结果为1