[issue29514] Add a test case that prevents magic number changes in minor releases

[Łukasz Langa]

Łukasz Langa added the comment:

I commented on the original issue where the magic number was changed. This broke the world at work for me. Our distribution mechanism for Python programs is zipped bundles of .pyc and .so files, the optimized variant doesn't keep .py files around. So suddenly otherwise correct bundles were refusing to start. Better yet, since the rollout of Python is staged and takes a while to do safely, new packages started appear with the new magic number that were refusing to start on 3.5.0. This was not a fun day :)

So, while I understand Brett's and Serhiy's reasoning, I'd be very careful about ever bumping magic numbers in minor releases again, and definitely communicate loudly if doing so.

Oh, if you're wondering why I even hit this problem before 3.5.3: since 3.5.2 had a few regressions we couldn't live with, I released 3.5.2+ from the latest commit on the 3.5 branch at the time (after checking the buildbots, running tests on our own, etc.). I repeated this feat with 3.6.0+ and again hit a thing that would likely upset some people in 3.6.1 (see #29519) but this time decided to patch it instead of just complaining ;)

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nosy: +lukasz.langa

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<http://bugs.python.org/issue29514>
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