Perl is mostly forwards and backwards compatible (or less generously it has frozen). Python is backwards compatible, but continues to add new features, and some

Perl is mostly forwards and backwards compatible (or less generously it has frozen). Python is backwards compatible, but continues to add new features, and some packages are rather enthusiastic about adopting these features quickly, and ending support for older versions of Python. It isn't as bad as other language communities (I'm looking at you Rust), and I would have at least given it an asterisk, but it certainly isn't as stable as Perl.