Python语言学习：解决python版本升级问题集合(python2系列→Python3系列)导致错误的总结集合

Python版本升级的原因

Text and binary data in Python 2 are a mess

Python版本升级问题及其解决方法

Python版本升级的原因

Python团队核心开发人员Brett Cannon用一篇文章解释了 Why Python 3 exists，部分内容见下边

Text and binary data in Python 2 are a mess

Quick, what does the following literal represent semantically?

'abcd'

If you're a Python 3 user you would say it's the string consisting of the letters "a", "b", "c", and "d" in that order.

If you're a Python 2 user you may have said the same thing. You may have also said it was the bytes representing 97, 98, 99, and 100. And it's the fact that there are two correct answers in Python 2 for what the str object represents that led to changing the language so that the single Python 3 answer was the only answer.

The Zen of Python says that "there should be one -- and preferably only one -- obvious way to do it". Having literals in the language that could represent either textual data or binary data was a problem. If you read something from the network, for instance, you would have to be very careful to either say the str object you returned represented binary data or textual data because there was no way to know once the object left your control. Or you might have a bug in your code where you were meant to translate that str object into textual data -- or something else entirely -- but you messed up and accidentally skipped that step. With the str object potentially represent two different semantic types it was hard to notice when this kind of slip-up occurred.

Now you might try and argue that these issues are all solvable in Python 2 if you avoid the str type for textual data and instead relied upon the unicode type for text. While that's strictly true, people don't do that in practice. Either people get lazy and don't want to bother decoding to Unicode because it's extra work, or people get performance-hungry and try to avoid the cost of decoding. Either way it's making an assumption that you will code well enough to not mess up, and we all know that we are fallible human beings who are in fact not perfect. If people's hopes of coding bug-free code in Python 2 actually panned out then I wouldn't consistently hear from basically every person who ports their project to Python 3 that they found latent bugs in their code regarding encoding and decoding of text and binary data.

This point of avoiding bugs is a big deal that people forget. The simplification of the language and the removal of the implicitness of what a str object might represent makes code less bug-prone. The Zen of Python points out that "explicit is better than implicit" for a reason: ambiguity and implicit knowledge that is not easily communicated code is easy to get wrong and leads to bugs. By forcing developers to explicitly separate out their binary data and textual data it leads to better code that has less of a chance to have a certain class of bug.

Python版本升级问题及其解决方法

1、
Python2系列：NameError: name 'raw_input' is not defined
Python3系列：python3.0版本后用input替换了raw_input

2、

Python2系列：import urllib2
Python3系列：import urllib.request as urllib2

3、

Python2系列：import thread
Python3系列：import _thread as thread

4、

Python2系列：except Exception,e:
Python3系列：except Exception as e:

5、

Python2系列：xrange
Python3系列：range

6、

Python2系列：unichr(i)
Python3系列：chr(i)

7、

Python2系列：
Python3系列：

8、

Python2系列：
Python3系列：

9、

Python2系列：
Python3系列：

10、

Python2系列：
Python3系列：

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