python 学习笔记 1

 

 -- 源自Python基础教程-第二版， 人民邮电出版社

 

 

• Ubuntu 11.10 自带了 python 2.7.2 and python3.2，若要IDLE或其他版本，则可以从Ubuntu Software Center download.

• Under ubuntu, I can run python(link to python2.7) or python2.7 or python3.2

• calculate 1 / 2

  in 2.7 , it's 0, in 3.2, it's 0.5. So, remember to use 1.0 / 2.0 or 1 // 2

• 3.0 / 2.0 => 1.5 ; 3.0 // 2.0 => 1.0 ; 3 // 2 => 1 ( note: // means 整除)

• % ==> 取余 ， e.g.; 5 % 2 ==> 1

• 2 ** 3 ==> 8 ; means 2 * 2 * 2

• int is 32bits, long is 64 bits

• 1000L, here “L” or “l” means long

• 8进制 010 = 10进制的8（仅在2.7中有效， 3.2 不能用）

• 16进制 0x12

• 变量赋值： x= 8

• e.g. x = 8;print(x); //注意：print x在2.7下可以工作， 3.2 不工作

• 字符串： “hello world” or 'hello world'

• 字符串转义： 'Let\'s go!' or “print quote(\”)”

• 字符串拼接： “Hello “ 'World' or “hello “ + 'World'

• 原始字符串用r开头， 如r'Let\'s go' 就是 'Let\\\'s go'; r相当于c#的@

  • but if x='hello', y=' world'; x+y is valid, x y is not valid

• unicode字符串 u'测试' , 在2.7可用， 3.2不能用，会出错。3.0+只有unicode字符串

• get input from console : x=input('intput a number')

• some built-in functions: pow(2,3) means 2**3 ==> 8;

  • abs(-1) ==> 1; round(5.2) ==> 5 ; round(5.8) ==> 6

• use module : e.g., import math

  • int(math.floor(5.2)) ==> 5;

• int(5.0) ==> 5

• if want import only one function from a module, not all the modules, use

• from math import sqrt

  • e.g.;

  • import sqrt from math

  • sqrt(100) ==> 10.0 // in this case, use sqrt directly, no need to add “math.” as prefix

• 支持复数， import cmath

• 有趣的__future__

• run in command line: python hello.py

• in ubuntu, run *.py as executable

  • first line like #!/usr/bin/env python

  • or #!/usr/bin/env python3.2

  • or #!/usr/binenv python2.7

• Comment : use #

  • # this is comment

• str() and repr() : how convert something to string

  • x=str(“ABC”) ;print(x) ==> ABC

  • y=repr(“ABC”);print(y) ==> 'ABC'

  • x=str(“Let's go”);print(x) ==> Let's go

  • y=repr(“Let's go”); print(y) ==> “Let's go”

  • temp=42; print(“The number is “ + repr(temp))

• str, repr和反引号是将python值转为支付串的3种方法， str让字符串易读，而repr和反引号则把结果字符串转换为合法的python表达式

• different between input() and raw_input() //only for 2.7

  • input() expects valid python expressions, like

    • 10,20,2.5

    • “hello world” # must contain quote in the beginning and the end

    • varName # varName must exists

  • 在3.2中，raw_input()不存在， input()的功能相当于2.7的input（）