python便利贴：python2-3兼容的代码

2024-01-19 13:58
文章标签 python 代码 兼容 python2 便利

本文主要是介绍python便利贴：python2-3兼容的代码，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

 

Table of Contents

支持包: python-future and six

关键语法

raising exceptions

defining exception and exception chaining

catching exceptions

Division

Long integers

Octal constants

Backtick repr

Unicode String/Byte String/BaseString

Imports relative to a package

Dictionaries

xrange vs range

map

raw_input & input

More

 

版权所有：013-2016 Python Charmers Pty Ltd, Australia.

作者： Ed Schofield.

许可：Creative Commons Attribution.

pdf版本： http://python-future.org/compatible_idioms.pdf

视频版本： http://www.youtube.com/watch?v=KOqk8j11aAI&t=10m14s

这个笔记列举了写面向未来的代码（即同时支持python2和3）的一些惯例

对小版本：

  • Python 2: 2.6+
  • Python 3: 3.3+

支持包: python-future and six

python-future是python2和python3之间缺少的兼容层， 其允许你使用一个单一的，干净的python 3.x-compatible基础代码去同时支持python 2和3。这样产生的开销是最小的（minimal overhead）。

我们使用pip install future可以import如下包:

import future
import builtins
import past
import futurize             
import pasteurize

 

目的相同共同相似的包还有python six，可以通过pip install six来安装，安装后，可import如下包：

import six

关键语法

  • print

python2 only:

[wlin@wlin rc_ci]$ ipython2
Python 2.7.5 (default, May 31 2018, 09:41:32) 
In [2]: print 'Hello' 
Hello

for both:

[wlin@wlin python_compatible]$ cat print.py 
from __future__ import print_function
print('hello','world')
[wlin@wlin python_compatible]$ python2 print.py 
hello world
[wlin@wlin python_compatible]$ python3 print.py 
hello world

 

  • raising exceptions

python2 only:

[wlin@wlin python_compatible]$ ipython2 
Python 2.7.5 (default, May 31 2018, 09:41:32) In [1]: raise ValueError, "dodgy value"
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-1-640428d25114> in <module>()
----> 1 raise ValueError, "dodgy value"ValueError: dodgy valueIn [3]: import sysIn [4]: traceback = sys.exc_info()[2]In [5]: raise ValueError, "dodgy value", traceback
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-5-91d00a6d59b2> in <module>()
----> 1 raise ValueError, "dodgy value", tracebackValueError: dodgy value

for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat raise_error.py 
raise ValueError('dodgy value')#from future.utils import raise_with_traceback
#raise_with_traceback(ValueError("dodgy value"))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 raise_error.py 
Traceback (most recent call last):File "raise_error.py", line 1, in <module>raise ValueError('dodgy value')
ValueError: dodgy value
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 raise_error.py 
Traceback (most recent call last):File "raise_error.py", line 1, in <module>raise ValueError('dodgy value')
ValueError: dodgy valuecarawangs-MacBook-Pro:python_compatible carawang$ cat raise_error.py 
#raise ValueError('dodgy value')from future.utils import raise_with_traceback
raise_with_traceback(ValueError("dodgy value"))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 raise_error.py 
Traceback (most recent call last):File "raise_error.py", line 4, in <module>raise_with_traceback(ValueError("dodgy value"))File "<string>", line 7, in raise_with_traceback
ValueError: dodgy value
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 raise_error.py 
Traceback (most recent call last):File "raise_error.py", line 4, in <module>raise_with_traceback(ValueError("dodgy value"))File "/usr/local/lib/python3.7/site-packages/future/utils/__init__.py", line 446, in raise_with_tracebackraise exc.with_traceback(traceback)
ValueError: dodgy value

  • defining exception and exception chaining

python3 only:

carawangs-MacBook-Pro:python_compatible carawang$ cat exception_class.py 
class DatabaseError(Exception):passclass FileDataBase:def __init__(self, filename):try:self.file = open(filename)except IOError as exc:raise DatabaseError('Failed to open') from excFileDataBase("non_existent_file.txt")carawangs-MacBook-Pro:python_compatible carawang$ vi exception_class.py 
YouCompleteMe unavailable: unable to load Python.
Press ENTER or type command to continue
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 exception_class.py 
Traceback (most recent call last):File "exception_class.py", line 7, in __init__self.file = open(filename)
FileNotFoundError: [Errno 2] No such file or directory: 'non_existent_file.txt'The above exception was the direct cause of the following exception:Traceback (most recent call last):File "exception_class.py", line 11, in <module>FileDataBase("non_existent_file.txt")File "exception_class.py", line 9, in __init__raise DatabaseError('Failed to open') from exc
__main__.DatabaseError: Failed to open
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 exception_class.py File "exception_class.py", line 9raise DatabaseError('Failed to open') from exc^
SyntaxError: invalid syntax

for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat exception_class.py 
from future.utils import  raise_fromclass DatabaseError(Exception):passclass FileDataBase:def __init__(self, filename):try:self.file = open(filename)except IOError as exc:raise_from(DatabaseError('Failed to open'), exc)FileDataBase("non_existent_file.txt")
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 exception_class.py 
Traceback (most recent call last):File "exception_class.py", line 9, in __init__self.file = open(filename)
FileNotFoundError: [Errno 2] No such file or directory: 'non_existent_file.txt'The above exception was the direct cause of the following exception:Traceback (most recent call last):File "exception_class.py", line 13, in <module>FileDataBase("non_existent_file.txt")File "exception_class.py", line 11, in __init__raise_from(DatabaseError('Failed to open'), exc)File "/usr/local/lib/python3.7/site-packages/future/utils/__init__.py", line 403, in raise_fromexec(execstr, myglobals, mylocals)File "<string>", line 1, in <module>
__main__.DatabaseError: Failed to open
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 exception_class.py 
Traceback (most recent call last):File "exception_class.py", line 13, in <module>FileDataBase("non_existent_file.txt")File "exception_class.py", line 11, in __init__raise_from(DatabaseError('Failed to open'), exc)File "/Users/carawang/Library/Python/2.7/lib/python/site-packages/future/utils/__init__.py", line 483, in raise_fromraise e
__main__.DatabaseError: Failed to open

  • catching exceptions

python2 only:

carawangs-MacBook-Pro:python_compatible carawang$ cat catch_exceptions.py 
try:raise ValueError('ValueError: dodgy value!')
except ValueError, e:print(e.message)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 catch_exceptions.py 
ValueError: dodgy value!
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 catch_exceptions.py File "catch_exceptions.py", line 3except ValueError, e:^
SyntaxError: invalid syntax
for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat catch_exceptions.py 
try:raise ValueError('ValueError: dodgy value!')
except ValueError as e:print(e.args)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 catch_exceptions.py 
('ValueError: dodgy value!',)
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 catch_exceptions.py 
('ValueError: dodgy value!',)

  • Division

python 2 and python 3 get different results:

carawangs-MacBook-Pro:python_compatible carawang$ cat division.py 
result = [2/3, 3/2]
print(result)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 division.py 
[0, 1]
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 division.py 
[0.6666666666666666, 1.5]

for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat division.py 
from __future__ import division
from past.utils import old_div
result = [2/3, 3/2]
print(result)
result = [old_div(2, 3), old_div(3, 2)]
print(result)
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 division.py 
[0.6666666666666666, 1.5]
[0, 1]
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 division.py 
[0.6666666666666666, 1.5]
[0, 1]

  • Long integers

Python3  取消了short integers而仅支持int。

for python2 only:

carawangs-MacBook-Pro:python_compatible carawang$ cat integer.py 
k = 123456789999
print(type(k))
lk = 123456789999L
print(type(lk))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 integer.py 
<type 'int'>
<type 'long'>
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 integer.py File "integer.py", line 3lk = 123456789999L^
SyntaxError: invalid syntax

for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat integer.py 
from builtins import int
from past.builtins import long
if isinstance(1234567890, int):print(type(1234567890))
if isinstance(1, (int, long)):print(type(1))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 integer.py 
<type 'int'>
<type 'int'>
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 integer.py 
<class 'int'>
<class 'int'>
 

  • Octal constants

for python2 only:

carawangs-MacBook-Pro:python_compatible carawang$ cat octal_constant.py 
from decimal import Decimal
print(int(Decimal(0644)))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 octal_constant.py 
420
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 octal_constant.py File "octal_constant.py", line 2print(int(Decimal(0644)))^
SyntaxError: invalid token
for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat octal_constant.py 
from decimal import Decimal
print(int(Decimal(0o644)))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 octal_constant.py 
420
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 octal_constant.py 
420

  • Backtick repr

for python2 only:

carawangs-MacBook-Pro:python_compatible carawang$ cat repr.py 
hello = "hello"
print(hello)
print(`hello`)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 repr.py 
hello
'hello'
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 repr.py File "repr.py", line 3print(`hello`)^
SyntaxError: invalid syntax
for both:
carawangs-MacBook-Pro:python_compatible carawang$ cat repr.py 
hello = "hello"
print(hello)
print(repr(hello))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 repr.py 
hello
'hello'
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 repr.py 
hello
'hello'

 

  • Unicode String/Byte String/BaseString

我们在此处仅列出兼容的代码

carawangs-MacBook-Pro:python_compatible carawang$ cat string.py 
a_bytestring = b'testing'
a_unicodestring = u'testing'
a_str = 'testing'print(type(a_bytestring))
print(type(a_unicodestring))
print(type(a_str))
# python3 does not support basetring()
#print(isinstance(a_bytestring, basestring))
print(isinstance(a_bytestring, str))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 string.py 
<type 'str'>
<type 'unicode'>
<type 'str'>
True
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 string.py 
<class 'bytes'>
<class 'str'>
<class 'str'>
False

  • Imports relative to a package

假设包结构为：

carawangs-MacBook-Pro:my_pkg carawang$ tree
.
├── __init__.py
├── sub_m1.py
└── sub_m2.py0 directories, 3 files

for both support:

carawangs-MacBook-Pro:my_pkg carawang$ cat sub_m2.py
TEST = True
carawangs-MacBook-Pro:my_pkg carawang$ cat sub_m1.py 
import sub_m2
print(sub_m2.TEST)
carawangs-MacBook-Pro:my_pkg carawang$ python2.7 sub_m1.py 
True
carawangs-MacBook-Pro:my_pkg carawang$ python3.7 sub_m1.py 
True

for both non-support:

carawangs-MacBook-Pro:my_pkg carawang$ cat sub_m1.py 
from . import sub_m2
print(sub_m2.TEST)
carawangs-MacBook-Pro:my_pkg carawang$ cat sub_m2.py 
TEST = True
carawangs-MacBook-Pro:my_pkg carawang$ python2.7 sub_m1.py 
Traceback (most recent call last):File "sub_m1.py", line 1, in <module>from . import sub_m2
ValueError: Attempted relative import in non-package
carawangs-MacBook-Pro:my_pkg carawang$ python3.7 sub_m1.py 
Traceback (most recent call last):File "sub_m1.py", line 1, in <module>from . import sub_m2
ImportError: cannot import name 'sub_m2' from '__main__' (sub_m1.py)
这个地方应该有问题。。。。。

  • Dictionaries

for python2 only:

carawangs-MacBook-Pro:python_compatible carawang$ cat dict.py 
heights = {'Fred': 175, 'Anne': 166, 'Joe': 192}
for key in heights.iterkeys():print(key)
for value in heights.itervalues():print(value)
for (key, value) in heights.iteritems():print(key, value)
keylist = heights.keys()
valuelist = heights.values()
print(isinstance(keylist, list))
print(keylist)
print(isinstance(valuelist, list))
print(valuelist)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 dict.py 
Anne
Joe
Fred
166
192
175
('Anne', 166)
('Joe', 192)
('Fred', 175)
True
['Anne', 'Joe', 'Fred']
True
[166, 192, 175]
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 dict.py 
Traceback (most recent call last):File "dict.py", line 2, in <module>for key in heights.iterkeys():
AttributeError: 'dict' object has no attribute 'iterkeys'
carawangs-MacBook-Pro:python_compatible carawang$ cat dict_cp.py 
heights = {'Fred': 175, 'Anne': 166, 'Joe': 192}
#for key in heights.iterkeys():
#    print(key)
#for value in heights.itervalues():
#    print(value)
#for (key, value) in heights.iteritems():
#    print(key, value)
keylist = heights.keys()
valuelist = heights.values()
print(isinstance(keylist, list))
print(keylist)
print(isinstance(valuelist, list))
print(valuelist)
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 dict_cp.py
False
dict_keys(['Fred', 'Anne', 'Joe'])
False
dict_values([175, 166, 192])
for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat dict.py 
heights = {'Fred': 175, 'Anne': 166, 'Joe': 192}
for key in heights.keys():print(key)
for value in heights.values():print(value)
for (key, value) in heights.items():print(key, value)
keylist = list(heights)
valuelist = list(heights.values())
print(isinstance(keylist, list))
print(keylist)
print(isinstance(valuelist, list))
print(valuelist)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 dict.py 
Anne
Joe
Fred
166
192
175
('Anne', 166)
('Joe', 192)
('Fred', 175)
True
['Anne', 'Joe', 'Fred']
True
[166, 192, 175]
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 dict
/usr/local/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7/Resources/Python.app/Contents/MacOS/Python: can't open file 'dict': [Errno 2] No such file or directory
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 dict.py 
Fred
Anne
Joe
175
166
192
Fred 175
Anne 166
Joe 192
True
['Fred', 'Anne', 'Joe']
True
[175, 166, 192]

 

  • xrange vs range

for python2 only:

carawangs-MacBook-Pro:python_compatible carawang$ cat range.py 
for i in xrange(5):print(i)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 range.py 
0
1
2
3
4
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 range.py 
Traceback (most recent call last):File "range.py", line 1, in <module>for i in xrange(5):
NameError: name 'xrange' is not defined

for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat range.py 
for i in range(5):print(i)
range_list = list(range(5))
print(isinstance(range_list, list))
print(range_list)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 range.py 
0
1
2
3
4
True
[0, 1, 2, 3, 4]
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 range.py 
0
1
2
3
4
True
[0, 1, 2, 3, 4]

  • map

for python2 only:

carawangs-MacBook-Pro:python_compatible carawang$ cat map.py 
def f(x):return int(x)+1
a_list = list(range(5))
b_list = [f(x) for x in a_list]
c_list = map(f, a_list)
print(type(c_list))
print(b_list)
print(c_list)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 map.py 
<type 'list'>
[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 map.py 
<class 'map'>
[1, 2, 3, 4, 5]
<map object at 0x106beaac8>

for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat map.py 
def f(x):return int(x)+1
a_list = list(range(5))
b_list = [f(x) for x in a_list]
c_list = list(map(f, a_list))
print(type(c_list))
print(b_list)
print(c_list)
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 map.py 
<type 'list'>
[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 map.py 
<class 'list'>
[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]

  • raw_input & input

for python2 only:

carawangs-MacBook-Pro:python_compatible carawang$ cat input.py 
name = raw_input('What is your name?')
print("hello {}".format(name))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 input.py 
What is your name?cara
hello cara
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 input.py 
Traceback (most recent call last):File "input.py", line 1, in <module>name = raw_input('What is your name?')
NameError: name 'raw_input' is not defined

 

for both:

carawangs-MacBook-Pro:python_compatible carawang$ cat input.py 
from builtins import input
name = input('What is your name?')
print("hello {}".format(name))
carawangs-MacBook-Pro:python_compatible carawang$ python2.7 input.py 
True
What is your name?cara
hello cara
carawangs-MacBook-Pro:python_compatible carawang$ python3.7 input.py 
What is your name?cara
hello cara

  • More

 https://python-future.org/compatible_idioms.html

这篇关于python便利贴：python2-3兼容的代码的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！


http://www.chinasem.cn/article/622637。

相关文章

Python的Darts库实现时间序列预测

Python的Darts库实现时间序列预测

《Python的Darts库实现时间序列预测》Darts一个集统计、机器学习与深度学习模型于一体的Python时间序列预测库,本文主要介绍了Python的Darts库实现时间序列预测,感兴趣的可以了解... 目录目录一、什么是 Darts？二、安装与基本配置安装 Darts导入基础模块三、时间序列数据结构与
阅读更多...
Python正则表达式匹配和替换的操作指南

Python正则表达式匹配和替换的操作指南

《Python正则表达式匹配和替换的操作指南》正则表达式是处理文本的强大工具,Python通过re模块提供了完整的正则表达式功能,本文将通过代码示例详细介绍Python中的正则匹配和替换操作,需要的朋... 目录基础语法导入re模块基本元字符常用匹配方法1. re.match() - 从字符串开头匹配2.
阅读更多...
Python使用FastAPI实现大文件分片上传与断点续传功能

Python使用FastAPI实现大文件分片上传与断点续传功能

《Python使用FastAPI实现大文件分片上传与断点续传功能》大文件直传常遇到超时、网络抖动失败、失败后只能重传的问题,分片上传+断点续传可以把大文件拆成若干小块逐个上传,并在中断后从已完成分片继... 目录一、接口设计二、服务端实现（FastAPI）2.1 运行环境2.2 目录结构建议2.3 serv
阅读更多...
C#实现千万数据秒级导入的代码

C#实现千万数据秒级导入的代码

《C#实现千万数据秒级导入的代码》在实际开发中excel导入很常见,现代社会中很容易遇到大数据处理业务,所以本文我就给大家分享一下千万数据秒级导入怎么实现,文中有详细的代码示例供大家参考,需要的朋友可... 目录前言一、数据存储二、处理逻辑优化前代码处理逻辑优化后的代码总结前言在实际开发中excel导入很
阅读更多...
通过Docker容器部署Python环境的全流程

通过Docker容器部署Python环境的全流程

《通过Docker容器部署Python环境的全流程》在现代化开发流程中,Docker因其轻量化、环境隔离和跨平台一致性的特性,已成为部署Python应用的标准工具,本文将详细演示如何通过Docker容... 目录引言一、docker与python的协同优势二、核心步骤详解三、进阶配置技巧四、生产环境最佳实践
阅读更多...
Python一次性将指定版本所有包上传PyPI镜像解决方案

Python一次性将指定版本所有包上传PyPI镜像解决方案

《Python一次性将指定版本所有包上传PyPI镜像解决方案》本文主要介绍了一个安全、完整、可离线部署的解决方案,用于一次性准备指定Python版本的所有包,然后导出到内网环境,感兴趣的小伙伴可以跟随... 目录为什么需要这个方案完整解决方案1. 项目目录结构2. 创建智能下载脚本3. 创建包清单生成脚本4
阅读更多...
SpringBoot+RustFS 实现文件切片极速上传的实例代码

SpringBoot+RustFS 实现文件切片极速上传的实例代码

《SpringBoot+RustFS实现文件切片极速上传的实例代码》本文介绍利用SpringBoot和RustFS构建高性能文件切片上传系统,实现大文件秒传、断点续传和分片上传等功能,具有一定的参考... 目录一、为什么选择 RustFS + SpringBoot？二、环境准备与部署2.1 安装 RustF
阅读更多...
Python实现Excel批量样式修改器(附完整代码)

Python实现Excel批量样式修改器(附完整代码)

《Python实现Excel批量样式修改器(附完整代码)》这篇文章主要为大家详细介绍了如何使用Python实现一个Excel批量样式修改器,文中的示例代码讲解详细,感兴趣的小伙伴可以跟随小编一起学习一... 目录前言功能特性核心功能界面特性系统要求安装说明使用指南基本操作流程高级功能技术实现核心技术栈关键函
阅读更多...
python获取指定名字的程序的文件路径的两种方法

python获取指定名字的程序的文件路径的两种方法

《python获取指定名字的程序的文件路径的两种方法》本文主要介绍了python获取指定名字的程序的文件路径的两种方法,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要... 最近在做项目，需要用到给定一个程序名字就可以自动获取到这个程序在Windows系统下的绝对路径，以下
阅读更多...
使用Python批量将.ncm格式的音频文件转换为.mp3格式的实战详解

使用Python批量将.ncm格式的音频文件转换为.mp3格式的实战详解

《使用Python批量将.ncm格式的音频文件转换为.mp3格式的实战详解》本文详细介绍了如何使用Python通过ncmdump工具批量将.ncm音频转换为.mp3的步骤,包括安装、配置ffmpeg环... 目录1. 前言2. 安装 ncmdump3. 实现 .ncm 转 .mp34. 执行过程5. 执行结
阅读更多...

Copyright China编程 23002807@qq.com

沪ICP备2023033072号-2