python学习记录（持续更新）--最最最基础的一部分（变量、字符串、运算符、常见函数）

写在前面

本系列教程针对有一定编程经验的伙伴快速入门python基础，一些涉及开发的常识问题，本文并不涉及。

几个常用的函数

print 打印 

print('*' * 10) =>  打印出10个*

input 获取输入

name = input('What is your name?')

int  float bool str 类型转换

num=int('12345')

　len upper lower  replace in 

course='Python for Beginners'
print(len(course)) =>20
print(course.upper())=>PYTHON FOR BEGINNERS

print(course.lower())=> python for beginners

print(course.title())=> Python For Beginners 首字母大写

print(course)=>Python for Beginners upper 并不会更改原有字符串

print(course.find('P')) => 0 找到第一个出现的索引 区分大小写

print(course.replace('Beginners','Absolute Beginners')) =>Python for Absolute Beginners  替换字符

print('Python' in course)=> True 是否包含某字符串

 range

for item in range(10):
    print(item) =>0~9

for item in range(5,10):
    print(item) =>5~9

for item in range(5,10,2): 步长
    print(item) => 5,7,9

 split

message="My name is Jaychou"
words=message.split(' ')
print(words)
=>['My', 'name', 'is', 'Jaychou']

几个细节

字符串输入的几种方式

print(' ')
print(" ")
print('''  
这种可换行输入
很方便

''')

　　索引

coutse='my name is Jay Chou'
print(coutse[0])

=> m

print(coutse[-1])
=> u

coutse='myname is Jay Chou'
print(coutse[0:3])
=>myn 从0开始算数3个字符打印

print(coutse[0:])
=>myname is Jay Chou 不指定结尾打印所有字符

print(coutse[:5])
=>mynam  开头不指定默认从0开始

coutse='myname is Jay Chou'
another = coutse[:]
print(another) 
=>myname is Jay Chou 用于clone字符串

格式化输入

first= 'Jay'
last= 'Chou'
msg = f'{first}[{last}] is a coder'
print(msg) =>Jay[Chou] is a coder

运算符

print(10/3) =>3.3333333333333335
print(10//3) =>3

print(10 % 3)=> 1

print((10**3)) =>1000 幂次运算

x = 10
x +=3
print(x) =>13

print(round(2.5)) => 2

print(round(2.51)) =>3 

round(80.23456, 2) :  80.23
round(100.000056, 3) :  100.0
round(-100.000056, 3) :  -100.0

print(abs(-2.5)) => 2.5 

运算函数模块 math

import  math 

print(math.ceil(2.1)) 天花板函数 向上取整 => 3

print(math.floor(2.1)) 向下取整 =>2