Those two controversial 2nd & 3rd paragraphs of my ch 1

Stefan Behnel stefan_ml at
Wed Jan 13 19:50:38 CET 2010

Daniel Fetchinson, 13.01.2010 17:30:
> Again, django has been ported to python 3, that's fine, everybody
> acknowledges that, but it's not the case that one code base works with
> both python versions.

Well, if the port is done via 2to3, you can install the same code base in 
Python 2 and Python 3, and the distutils install mechanism will run an 
automated transformation over the code during the installation. If there is 
no manual interaction required to run the code on both platforms, I would 
say that qualifies as "one code base works with both Python versions". It's 
not different from generating code or specialised config files during the 
installation or similar things.

 > I think django and cheetah
 > doesn't count because they simply take their python 2 code, run it
 > through 2to3 which gives them a python 3 code (I could be wrong
 > though). Two codes for the two python versions.

But just one code base that has to be maintained. And I think the 
maintenance is the main aspect here.

> Just to be clear I'm looking for an example where one given
> code runs on python 2 and 3 unmodified.

lxml for example. Not only the Cython compiled part (which is automatically 
portable anyway), also all of its Python code base and its entire test 
suite. It runs on all Python versions from 2.3 through 3.1, and it doesn't 
use 2to3 or any other kind of code modification.

The regular Python code base was almost trivial to port, but porting the 
test suite was actually quite involved. The main reasons for that were a) 
doctests and b) the requirement to test exactly string input/output and 
exactly unicode input/output on both platforms. Most code simply doesn't 
have that requirement, but lxml does.


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