Had Python 3 stuck to relatively simple changes like converting to the print() function, making a few libraries more consistent, etc. then it would be closer to the C++ compatibility-breaking changes proposed here.  Instead, Python 3 went far beyond things that were easily convertible and it isn&#x27;t surprising that adoption was greatly slowed.<p>C++ has <i>atrocious</i> defaults, where you have to add a bunch of keywords and do all these things just to make the simplest classes do the &quot;right&quot; thing.  It&#x27;s long overdue for some new behaviors.<p>Adding things like &quot;override&quot; to existing code has been an absolute joy.  It has <i>already</i> prevented errors during maintenance in projects at work.  It is well worth a few days of ugly revision control logs.<p>There are lots of ways to smooth a backward-incompatible transition for C++ on a larger scale.  For instance, they could enable it on a file-by-file basis by having some new declaration like &quot;using c++17;&quot; (or better still, require only the old, out-of-date files to add this declaration in order to continue compiling).