Python Learning Notes

InstallationLinux

Linux has come with Python, and my Centos7 comes with Python2.7.4, and I have updated the version by installing it from the source.

<!--lang: sh-->#!/bin/bash#源码安装wget https://www.python.org/ftp/python/2.7.9/Python-2.7.9.tgztar -zxvf Python-2.7.9.tgzcd Python-2.7.9#编译安装./configuremakemake install

Install PIP (recommended installation, not required)

Pip is a package manager that is easy to install after installation using the framework and dependent packages. Recommended installation.

<!--lang: sh-->#!/bin/bashwget https://bootstrap.pypa.io/get-pip.pypython get-pip.py

Hello World

>>> print ‘hello, world‘hello, world>>> exit()

Editor

It is recommended to use notepad++ under Vim,windows.

hello_world.py

#!/usr/bin/env python# -*- coding:utf8-*-# 第一行用于在Linux下被识别从而直接运行#第二行用于定义此文件的字符编码是utf8，防止乱码，这是一个好习惯#print可以使用以下两种形式来输出字符到控制台，推荐第二种，可以兼容Python3print ‘Hello World‘print(‘Hello World‘)#可以用逗号分隔每个字符串，打印出来遇到逗号会输出一个空格print ‘Hello‘,‘World‘#读取用户输入的字符并赋予name变量name = raw_input()

Run

<!--lang: sh-->python hello_world.py

Basis

• #Start with a comment
• :End is code block, code block indentation recommended four spaces

Data typeDigital

• Integers: For example 1 100 , 16 is the 0x beginning of the binary, for example0xff00
• Floating-point numbers: For example 3.14 , scientific notation replaces 10 with E, and the 9-1.23x10 is 1.23e9 or 12.3e8
  Note: integer operations are always accurate, and floating-point numbers may be rounded

String

• ‘‘ "" any text in or enclosed, escaped, used to \ escape single quotes, double quotes, and special characters (such as line breaks)
• r‘‘Represents the original string and does not need to be escaped
• ‘‘‘我是内容‘‘‘These three quotes (single and double lines) expand to indicate the text that can be wrapped
• r‘‘‘我是内容‘‘‘Represents multiple lines of raw string and does not need to be escaped
• u‘‘Represents a Unicode string
• String Formatting ' Hello,%s '% ' world '

Boolean value

• True
• False
  Boolean values can be used and , or and not operations

Null value

None

Variable

The type of the variable depends on the type of the first assignment.

a = 1

Constant

In Python, the variable in all capitals is constant (the value can still be changed).

PI = 3.14

Type judgments and Conversions

a = ‘123‘# 判断类型type(a)# 转换为int，其他类型同理int(a)## 转换函数表int(x [,base ])                #将x转换为一个整数long(x [,base ])             # 将x转换为一个长整数float(x )                        #将x转换到一个浮点数complex(real [,imag ])  #创建一个复数str(x )                           #将对象 x 转换为字符串repr(x )                        #将对象 x 转换为表达式字符串eval(str )                      #用来计算在字符串中的有效Python表达式,并返回一个对象tuple(s )                       #将序列 s 转换为一个元组list(s )                           #将序列 s 转换为一个列表chr(x )                          #将一个整数转换为一个字符unichr(x )                     #将一个整数转换为Unicode字符ord(x )                          #将一个字符转换为它的整数值hex(x )                          #将一个整数转换为一个十六进制字符串oct(x )                           #将一个整数转换为一个八进制字符串

SequenceList (lists)

classmates = [‘Michael‘, ‘Bob‘, ‘Tracy‘]#list中元素个数（得到3）len(classmates)#最小元素（得到‘Bob‘）min(classmates)#最大元素（得到‘Tracy‘）max(classmates)# 访问元素（得到‘Michael‘）classmates[0]# 倒数第一个元素（得到‘Tracy‘）classmates[-1]# 追加元素classmates.append(‘Adam‘)# 位置1插入元素，后面元素会依次后推 classmates.insert(1, ‘Jack‘)# 删除末尾元素classmates.pop()# 删除位置 1 的元素classmates.pop(1)del classmates[1]# 删除片段del classmates[i: j]# 替换元素classmates[1] = ‘Sarah‘#切片（选取第一个到第二个元素组成新列表）classmates[1: 2]#切片（选取第一个到第三个元素组成新列表，每隔两个，按照原始list，得到‘Bob‘）classmates[1: 3: 2]# 不同类型元素L = [‘Apple‘, 123, True]# list嵌套（list做为list的一个元素）s = [‘python‘, ‘java‘, [‘asp‘, ‘php‘], ‘scheme‘]#取得‘php‘（相当于二维数组）print(s[2][2])#序列连接（两个列表组成新列表）classmates  + [‘lucy‘, ‘joe‘]#序列中的元素重复三次classmates * 3#元素在列表中是否存在isHave = ‘Bob‘ in classmates#转为序列（得到[‘P‘, ‘y‘, ‘t‘, ‘h‘, ‘o‘, ‘n‘]）list(‘Python‘)

Tuple (tuple)

Once the definition is immutable. Gets the same element as the list, if there is only one element in the tuple, a comma must be used to differentiate it from the operator.

classmates = (‘Michael‘, ‘Bob‘, ‘Tracy‘)# 单元素元组classmates = (‘Michael‘,)

Dict and setDict

d = {‘Michael‘: 95, ‘Bob‘: 75, ‘Tracy‘: 85}#取值（不存在报错）d[‘Michael‘]#取值，不存在返回`None` d.get(‘Thomas‘)#取值，不存在返回自定义值`-1` d.get(‘Thomas‘, -1)#定义值d[‘Adam‘] = 67#删除键值对d.pop(‘Bob‘)del (d[‘Bob‘])#键列表dict.keys()#值列表dict.values()#键值对元组列表dict.items()#遍历for (k, v) in dict.items():    print ‘dict[%s] =‘ % k, v

Set

Collection of elements that are not duplicated

#定义，需要将list转化为set，自动过滤重复s = set([1, 2, 3])#添加s.add(4)#删除s.remove(4)#交集set([1, 2, 3]) & set([2, 3, 4])#并集set([1, 2, 3]) | set([2, 3, 4])

Conditional Judgment and circulationConditions

Both elif and else can be omitted. Conditions non-0 value, non-empty string, not empty list, etc., is judged True , otherwise False .

if <条件判断1>:    <执行1>elif <条件判断2>:    <执行2>elif <条件判断3>:    <执行3>else:    <执行4>

Cycle

#遍历列表names = [‘Michael‘, ‘Bob‘, ‘Tracy‘]for name in names:    print name# 便利列表2for x in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]:    print x# 遍历列表3，等效2for x in range(101):    print x# while循环（按条件循环）n = 99while n > 0:    print n    n = n - 2

Python Learning Notes