[Python-Dev] No 2.x->3.x porting documentation? (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Mon Feb 16 10:29:46 CET 2009

I'm making a naive stab at converting nose to Python3 so I can hopefully run the lockfile test cases under Python 3. (Again, I'm offline and have no idea at this point if it's been done already.) I ran 2to3 then tried installing. I got an immediate error about the compiler.consts module being missing. (All nose does is import COGENERATOR from compiler.consts.) I found that in the inspect module. Then it complained about ClassType being missing from the types module. I found no mention of changes to the types module in Misc/NEWS or Doc/whatsnew/3.0.rst. I didn't find anything which looked like a "porting" document.

If neither of these changes could be handled by 2to3 I think it would have been useful to at least document the changes (in whatsnew/3.0.rst?) and maybe offer humans some workaround ideas. If there is a wiki page collecting porting wisdom it should be referenced. If I'm missing something fundamental about how people are expected to approach porting 2.x code to 3.x, please let me know.

I think you are missing the fact that it is nearly impossible to produce a complete list of changes between 2.x and 3.x, or, if such a list would be produced, it would have the size of the unified diff between the source trees.

Instead, porters are expected to think a bit on what might have been the most natural cause for a change (of course, some changes are arbitrary and have no cause other than personal taste). For example, ClassType used to be the type of old-style classes. Now that old-style classes are gone, ClassType is gone as well (FWIW in 59217, and indeed without a mentioning in NEWS, or even in the commit message). The removal of the compiler package is mentioned in NEWS:

http://svn.python.org/view/python/branches/p3yk/Misc/NEWS?rev=55322&view=markup

Regards, Martin

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