[Python-Dev] Python 2.x and 3.x use survey, 2014 edition (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Wed Dec 17 07:52:39 CET 2014

On 17 December 2014 at 10:45, Chris McDonough <chrism at plope.com> wrote:

On 12/16/2014 03:09 AM, Barry Warsaw wrote:

On Dec 16, 2014, at 02:15 PM, Skip Montanaro wrote:

While he doesn't explicitly say so, I got the distinct impression reading his recent blog post that he supports one source, not forked sources.

I've ported a fair bit of code, both pure-Python and C extensions, both libraries and applications. For successful library ports to Python 3 that need to remain Python 2 compatible, I would almost always recommend a single source, common dialect, no-2to3 approach. There may be exceptions, but this strategy has proven effective over and over. I generally find I don't need six but it does provide some nice conveniences that can be helpful. With something like tox running your test suite, it doesn't even have to be painful to maintain. I'll agree; with tox and some automated CI system like travis or jenkins or whatever, once you've done the port, it's only a minor nuisance to maintain a straddled 2/3 codebase. Programming in only the subset still isn't much fun, but maintenance is slightly easier than I expected it to be. "Drive by" contributions become slightly harder to accept because they often break 3 compatibility, and contributors are often unable or unwilling to install all the required versions that are tested by tox.

It's worth noting that the last problem can potentially be mitigated to some degree by taking advantage of the new "pylint --py3k" feature making it easier to check that code is 2/3 source compatible without needing a local copy of Python 3 to test against, and without needing to adhere to pylint's other checks.

As far as Marko's suggestion of maintaining two code bases go, that's what we do for the standard library, and we've never advised anyone else to do the same. Even before experience showed the source compatible approach was more practical, the original advice to third party developers was to use 2to3 to automatically derive the Python 3 version from the Python 2 version and address any compatibility issues by modifying the Python 2 sources.

Cheers, Nick.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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