[Python-Dev] Difference in RE between 3.2 and 3.3 (or Aaron Swartz memorial)

[Matej Cepl]

On 2013-03-06, 18:34 GMT, Victor Stinner wrote:
> In short, Unicode was rewritten in Python 3.3 for the PEP 393. It's
> not surprising that minor details like singleton differ. You should
> not use "is" to compare strings in Python, or your program will fail
> on other Python implementations (like PyPy, IronPython, or Jython) or
> even on a different CPython version.

I am sorry, I don't understand what you are saying. Even though 
this has been changed to 
https://github.com/mcepl/html2text/blob/fix_tests/html2text.py#L90 
the tests still fail.

But, Amaury is right: the function doesn't make much sense. 
However, ...

when I have “fixed it” from
https://github.com/mcepl/html2text/blob/master/html2text.py#L95

def onlywhite(line):
     """Return true if the line does only consist of whitespace characters."""
     for c in line:
         if c is not ' ' and c is not '  ':
             return c is ' '
     return line

to 
https://github.com/mcepl/html2text/blob/fix_tests/html2text.py#L90

def onlywhite(line):
     """Return true if the line does only consist of whitespace 
     characters."""
         for c in line:
            if c != ' ' and c != ' ':
               return c == ' '
         return line

tests on ALL versions of Python are suddenly failing ...  
https://travis-ci.org/mcepl/html2text/builds/5288190

Curiouser and curiouser! At least, I seem to have the point,
where things are breaking, but I have to admit that condition
really doesn’t make any sense to me.

> Anyway, you spotted a missed optimization: it's now "fixed" in
> Python 3.3 and 3.4 by the following commits.

Well, whatever is the problem, it is not fixed in python 3.3.0
(as you can see in
https://travis-ci.org/mcepl/html2text/builds/4969045) as I can
see on my computer. Actually, good news is that it seems to be
fixed in the master branch of cpython (or the tip, as they say in
the Mercurial world).

Any thoughts?

Matěj