Python 3 was released in 2008, Python 2.7 had some kind of release last year but my memory is that up to about 2013 there was still a serious question of 2.7 vs 3 when you started a new project ("I know we should use 3, but then we can't have x-lib!").

So it happened once but it took up about 25% of the last 20 years.

A little. But there were changes from e.g. 2.5 to 2.7 and in the earlier 3.x versions that broke stuff. That never happened with Perl code here.