Stop using python 3 as an example. It is really tiring to hear about an extreme case of gross incompetence over and over again, while over in say the Grails/Spring ecosystem I don't even bother upgrading Grails 3 or 4 Plugins to Grails 6, because they still work as intended. When you upgrade a plugin from one version to the next, you're just swapping out build.gradle, gradle wrapper and a bunch of ancillary properties files. The build system changes, but everything else stays the same with only a tiny tiny minority of plugins being affected and even then the things that broke are absolute nonissues that can be fixed relatively quickly.

It is kind of interesting how the python community hasn't learned a thing from python 2/3. The problem isn't breaking backwards compatiblity. Probably the biggest mistake you can do is act like breaking backwards compatiblity is a big deal, therefore you should pile up as many breaking changes as possible and release them all at once so as to maximize pushback and upgrade friction.

It is in fact the exact opposite. If you break 10 libraries out of a million, you as the language developer can step in and upgrade them on behalf of the original maintainer. The users increment a library version when they increment the language version and done.

▲ bluGill 7 months ago | parent [-]

Python3 is a great example. They looked at what others had done. They carefully thought about the problem. They build tools to migrate. They announced plans. They really thought they had found a better answer that would work out because they had planned for everything.

Of course we are now looking at things in hindsight and see what didn't work.

▲ earthboundkid 7 months ago | parent [-]

It's really important to be clear about the lessons to be learned from Python 3.

1. Forward compatibility is more important than backward compatibility. 2. Automated refactoring tools don't help with 1.

The problem wasn't that they broke a lot in Python 3. It was that you couldn't write your Python 2 in such a way as to be compatible with it until well into the transition process as the six package got popular and the devs fixed needlessly broken things in Python 2.

▲ samatman 7 months ago | parent [-]

I would suggest languages facing the same problem learn from Perl 5's success, rather than the various failures of Python 3.

Every† minor point release of Perl 5 creates backward-incompatible changes. These can be opted into individually, or on a per-file basis by simply specifying the version of Perl used. It all works. Differently-versioned Perl code can call each other as much as it likes.

There was never any reason why Python 3 needed to be anything other than Python 2 with this at the top of the file:

  use Python 3.n

For various values of `n`. Perhaps when enough time passes, that's just Python now, and you have to copy-paste this into all the legacy code:

  use Python 2

That's it. Any language can do this, they just have to decide not to make life hard for everyone.

[†] Perhaps not literally every, but it may as well be.

▲

bluGill 7 months ago | parent [-]

There are many options with pros and cons. Python was aware of them. They made what looked like a reasonable decision to take a different paths. On hindsight we know of the problems but you could not predict them with confidence in advance. (some may have predicted it but they would admit to guessing if they are honest)

	▲	samatman 7 months ago \| parent [-]
		Sure, not interested in changing the past, for many reasons not least of which is that it appears to be impossible. The Python team surely did not go in to Python 3 blindly, but they botched it anyway. What I mean to say is that Python as a negative example only goes so far, because an example of failure isn't a template for success. So "don't do what Python did" carries limited value for a language looking to make breaking changes. For a language looking to make a major point release, that's the future, and the future can be changed; this is what I'm interested in here. "Do what Perl 5 did" (and do not do what Perl 6 did, up to the point it got renamed) is a great place to start, however, because it worked, works, is working. Languages are different enough that it isn't a completely transferable experience, but there's a lot to learn there.