Python3 And Python2 The difference of
be based on python3 Talking about python3 And python2 The difference of . Because of the current mainstream Python3, But I used to use Python2 Project done , We have to maintain it , So as python Worker , You have to understand the differences , among ,Python2 Yes ASCII str() type ,unicode() It's alone , No byte type . and Python3.X The source file defaults to utf-8 code , And a byte class ：byte and bytearrays. This makes the following code legal ：
Coding differences ：
I = 'zhongguo' print( I ) Python3 result ：zhongguo
notes ：python2 China is illegal , No matter code or comment, Chinese characters cannot appear , Unless stated ：#!/usr/bin/python -*- coding: UTF-8 -*-
As a default specification or code literacy , You don't usually use Chinese characters , Try to make the code as good as possible python spot ！
python3 And python2 The biggest difference is print Output , Please refer to print Use ：https://blog.csdn.net/u010986753
Python 3 In the version print The sentence is gone , In its place print() function .
print differences ：
Output correctly "life is short we neeed python！" The code is as follows ：
print('life is short we neeed python!')Python3 result ：life is short we neeed python！
Python2 Print in ：
print "life is short we neeed python!"/
print 'life is short we neeed python!'/
print ('life is short we neeed python!') The output is the same ！
Divide the difference
> print(7/3)>
Python3 result ：2.3333333333333335
> Python2 result ：2
> Python3 It means division print(7//3)
The difference of inequality ：
Python2 There are not two ways of writing != and <>
Python3 Removed from <>, Only != A way of writing
The difference between integers ：
Python2 There is an integer in —int And long -long
Python3 There is only one type of integer in —int
The difference in cue information ：
Python2 in raw_input( " Prompt information " ) and input( " Prompt information " )
Python3 There are only input( " Prompt information " )
Differences in opening files ：
Python2 in file( ..... ) or open(.....)
Python3 There are only open(.....)
map、filter and reduce The difference of ：
Python2 In interactive mode ：
>>> map <built-in function map> >>> filter<built-in function filter> >>> reduce<built-in function reduce>
The result types they output are all lists :
>>> map(lambda x:x +2, [4,1,3]) [6, 3, 5] >>> filter(lambda x:x %2 ==0,range(9)) [0, 2, 4, 6, 8]
Python3 In interactive mode ： They go from functions to classes , secondly , Their return result is also an iterative object from the original list
>>> map<class 'map'> >>> map(print,[1,2,3]) <map object at 0x10d8bd400> >>> filter<class 'filter'> >>> filter(lambda x:x % 2 == 0, range(10)) <filter object at 0x10d8bd3c8>
Traversal tuples For the more high-end reduce function , It's in Python3 China no longer belongs to built-in 了 , Moved to functools Modules . If you need to write a list parsing that traverses tuples ,Python2 You don't need to put parentheses around the tuple value . stay python3 in , These brackets are required .
Python2 in [ i for i in 1, 2]
Python3 in [i for i in (1,2)]
Get a range of numbers
python２ in , There are two ways to get a range of numbers ：range(), Return a list , also xrange(), Returns an iterator .
python3 in ,range() Return iterator ,xrange() No longer exist .
Python2 in [ i for i in 1, 2]
Python3 in [i for i in (1,2)]
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