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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Why has python3 been created as a seperate language where there is still python2.7 ?
Date: Wed, 27 Jun 2012 17:14:42 -0400
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Xref: csiph.com comp.lang.python:24542

On 6/27/2012 3:08 PM, Serhiy Storchaka wrote:
> On 27.06.12 14:22, Stefan Behnel wrote:
>> For comparison, the revival of the "u" string prefix in Py3.3 is a simple
>> change in the parser grammar that's easy to maintain

> And even this simple change has caused unexpected issues (see issues
> #15054 and #15096), which were not predicted by the preceding stormy
> discussion.

#15054 was mostly not about 'u'.

http://bugs.python.org/issue15096 is about 'u', or rather about the post 
discussion extension of 'u' to 'ur'. During the discussion of 'u', I 
predicted that adding 'innocuous' 'u' would lead to efforts to add other 
things. Adding 'ur' was the first example of that. We are fortunate that 
someone decided to test the new feature at the alpha stage. At least the 
near fiasco is a lesson.

> IMHO, the negative consequences of this change are undervalued.

Another prediction: people who code Python without reading the manual, 
at least not for new features, will learn about 'u' somehow (such as by 
reading this list) and may do either of the following, both of which are 
bad.

1. They will confuse themselves by thinking that 'u' actually means 
somethings. They may then confuse others by writing about its supposed 
meaning. This might get amusing.

2. They will use 'u' in Python 3 only code, thereby making it 
incompatible with 3.2-, even if it otherwise would not be.

These two actions will reinforce each other.

-- 
Terry Jan Reedy