Perl's decline was cultural

Overwhelmingly, what gets removed is from the standard library, and it's extremely old stuff. As recently as 3.11 you could use `distutils` (the predecessor to Setuptools). And in 3.12 you could still use `pipes` (a predecessor to `subprocess` that nobody ever talked about even when `subprocess` was new; `subprocess` was viewed as directly replacing DIY with `os.system` and the `os.exec` family). And `sunau`. And `telnetlib`.

Can you show me a real-world package that was held back because the code needed a feature or semantics from the interpreter* of a 3.x Python version that was going EOL?

> Python interpreter: if you can tell "print" is being used as a keyword rather than a function call, in order to scold the programmer for doing that, you can equally just perform the function call.

No, that doesn't work because the statement form has radically different semantics. You'd need to keep the entire grammar for it (and decide what to do if someone tries to embed a "print statement" in a larger expression). Plus the function calls can usually be parsed as the statement form with entirely permissible parentheses, so you have to decide whether a file that uses the statement should switch everything over to the legacy parsing. Plus the function call affords syntax that doesn't work with the original statement form, so you have to decide whether to accept those as well, or else how to report the error. Plus in 2.7, surrounding parentheses are not redundant, and change the meaning:

  $ py2.7 
  Python 2.7.18 (default, Feb 20 2025, 09:47:11) 
  [GCC 13.3.0] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  >>> print('foo', 'bar')
  ('foo', 'bar')
  >>> print 'foo', 'bar'
  foo bar

That is not what I was getting at. What I was saying is that, if you write code for perl 5.20 and mark it "use 5.20.0;", then that's it, you're done, code never needs to change again. You can bring in newer perl interpreters, you can upgrade, it's almost certainly not going to break.

You can even write new code down the line in Perl 5.32 which wouldn't be possible in 5.20, and the 5.20 code wouldn't be valid in 5.32, but as they're both declaring which version of the language they're written in, they just seamlessly work together in the same interpreter.

Compared to Python's deliberate policy, which is they won't guarantee your code will still run after two minor releases, and they have a habit of actively removing things, and there's only one version the interpreter implements and all code in the same interpreter has to be be compatible with that version... it means a continual stream of having to update code just so it still runs. And you don't know what they're going to deprecate or remove until they do it, so it's not possible to write anything futureproof.

> in 2.7, surrounding parentheses are not redundant,

That is interesting, I wasn't aware of that. And indeed that would be a thorny problem, moreso than keeping a print statement in the grammar.

Fun fact: the parentheses for all function calls are redundant in perl. It also flattens plain arrays and does not have some mad tuple-list distinction. These are all the same call to the foo subroutine:

    foo "bar", "baz"
    foo ("bar", "baz")
    foo (("bar", "baz"))
    foo (("bar"), "baz")
    foo (((("bar")), "baz"))

They don't guarantee that the entire standard library will be available to you two minor releases hence. Your code will still run if you just vendor those pieces (and thanks to how `sys.path` works, and the fact that the standard library was never namespaced, shadowing the standard library is trivial). And they tell you up front what will be removed. It is not because of a runtime change that anything breaks here.

Python 3 has essentially prevented any risk of semantic changes or syntax errors in older but 3.x-compatible code. That's what the `__future__` system is about. The only future feature that has become mandatory is `generator_stop` since 3.7 (see https://peps.python.org/pep-0479/), which is very much a corner case anyway. In particular, the 3.7-onward annotations system will not become mandatory, because it's being replaced by the 3.14-onward system (https://peps.python.org/pep-0649/). And aside from that again the only issue I'm aware of (or at least can think of at the moment) is the async-keyword one.

> And you don't know what they're going to deprecate or remove until they do it

This is simply untrue. Deprecation plans are discussed in public and now that they've been burned a few times, removal is scheduled up front (although it can happen that someone gives a compelling reason to undo the deprecation).

It's true that you can't make your own code, using the standard library (which is practically impossible to avoid), forwards-compatible to future standard libraries indefinitely. But that's just a matter of what other code you're pulling in, when you didn't write it in the first place. Vendoring is always an option. So are compatibility "forward-ports" like https://github.com/youknowone/python-deadlib. And in practice your users are expecting you to put out updates anyway.

And most of them are expecting to update their local Python installations eventually, because the core Python team won't support those forever, either. If you want to use old FOSS you'll have to accept that support resources are limited. (Not to mention all the other bitrot issues.)