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Comment by bandrami | Hacker News Reader

> at this point there is no reason to not use Python 3 for new projects

Sure there is: Python 2 isn't going to change on me again. Python 3 might.

Why on earth do people downvote that? I want a language that isn't going to change. Every single other language community seems to understand that, but something about it pisses off Python people.

You're claiming to know the future of Python better than "Python people" know the future of Python.

Python has changed incompatibly once in 26 years, and never plans to do it again, yet you're making it sound like an ongoing pattern. What language are you going to run to that has that kind of track record?

POSIX sh?

Have fun with that?

Real 'fun' to program in - with strict POSIX shell, functions cannot even have local variables.

30 years later, scheme is still scheme. A different report has come out, and some compilers choose to implement it. But the language hasn't changed. See my point?

I particularly don't see your point when it comes to Scheme. The Scheme I learned in 2002 (MIT Scheme) is all but abandoned. I was one of the people hired to rewrite MIT's course code from MIT Scheme to DrScheme, which was definitely not compatible. DrScheme itself has been superseded by Racket, except at that point MIT changed all their CS courses and rewrote everything again in Python.

What Scheme implementation do you use that has never broken compatibility and continues to be maintained?

Of course code being data in Scheme you could easily write program that processes scheme code and transforms it to a different syntax. I would assume this would be harder with Python code.

Not particularly. Like any sane programming language, Python has an AST. That's code as data. For porting, it doesn't particularly matter to be able to treat code as data while running that code.

There are tools that use the AST to translate Python 2 to Python 3, such as python-future. (Unfortunately, one of the things the core Python devs botched about the transition is that they put an awful, incomplete, broken one of these named 2to3 in the standard Python distribution.)

Racket's approach is rather different; they just support all the different Scheme/Racket syntaxes and standard libraries PLT has ever supported, with the same runtime. This doesn't include MIT Scheme but there is a syntax for the subset of it used in SICP. I don't think they have anything that converts code between the syntaxes.

I wouldn't mind seeing Python also use that approach -- a Python 3 runtime that runs Python 2 code (and maybe borks your Unicode, which is fine because people who stay on Python 2 clearly don't care that much about Unicode, and that's their prerogative). I'm convinced the only reason no such thing exists is that the first person who makes it would become responsible for everybody's awful old Python 2 code. Maybe in 2020 someone will make it and charge money for it.

If you read the original Scheme report, you'll notice that it's full of example programs, zero of which run on modern Schemes. They're full of operators that Scheme doesn't have anymore, like BLOCK, PROGN, CATCH, ASET, -$, *$, //$, EVALUATE!UNINTERRUPTIBLY, START!PROCESS, etc.

> Python has changed incompatibly once in 26 years

That's not true. Every change breaks some behavior, even if it's not throwing an Exception where one used to be thrown. Things are still being deprecated and removed in new releases.

On top of that, by adding new syntax in 3.7+, libraries may become incompatible with the system-provided installation. That won't happen with 2.7 libraries.

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