Well sure, but if anything that's just a case study in how much inertia actually matters in practice.
I'd argue that it's a proof that it doesn't matter that much. Of course, there's a decent amount of inertia (COBOL is still popular! And I know a lot of researchers that use F77) but Python 3.0 is just 8 years old, and 3.0 wasn't that stable. In less than a decade, they'll have a switch, and they could have had it faster (they shouldn't have put the end of life of Python that far in 2020).
Should you break a couple of legacy syntax with, let's say, C++X17, granted, there'll people that will stick with older versions, but honestly, it's already the case. I'm not sure that X11 is even that widespread. After all, the C > C++ jump has broken things, that hasn't stopped C++ popularity.
There are still reasons to use Python 2 over 3.
You'll find reasons for most things, but really valid ones, that's sometimes harder
5 years ago, definitively. Now, not that many.
I grant you, rewriting code is expensive (though not that much in this case), but more often than not, if 2to3 doesn't work, it's because the code is poorly written / ambiguous to begin with.
Most importantly, the OS distribution you're using ships with Python 2
Which one? Most Linux distribution are jumping on Py3k... like RedHat, Fedora or Ubuntu (though in Ubuntu case, they kept both).
I'll grant you Debian, but it's a special case, it shouldn't be a distribution for end users, and if you use it, you know that you're far behind the times (I mean, the last THREE times I installed a stable, I had to switch to testing because my processor or something else was too "recent" to be supported... I had freezes because of Sandy bridge integrated GPU, for example). And while Python (2) is the default, none are technically in the base distribution (priorities are standard and optional, resp., if I'm not mistaken). I hope Buster will make the switch.
Python doesn't come with Windows, and I'm pretty sure that most popular distributions lean towards Python3 (I'm not sure Python(x,y) made the jump, but I'm not sure it's still really alive).
and Python makes side by side installs a pain the ass (I'm looking at you PYTHONPATH, you son of a bitch)
Is it an OS-X issue?
Because it's dead easy on Windows and on Linux. I have both installed on both OS (because students are allowed to code in both, even if all people I know teach Py3k, so I may need to check exotic Python 2 syntaxes I forgot), with a bunch of packages (in two versions), and I haven't had any issue on either.
On Debian, you don't even have to think about it, the modules are stored in directories on a per-version basis (such as /usr/lib/python3.4), and you choose 2 or 3 at installation (be it using aptitude or "manual" install).
On Windows with Conda, not only you can have both, but you can have multiple instances of both using enviromnents (I have 3.4, 3.5 and 3.6 on the same machine). You need to look how it works, but it's quite straightforward. In fact, some version of Pyzo+Conda install both, and you can switch the version in a droplist in the IDE. You can even have both running at the same time.
I admit, each time I had to deal with modules on a OS-X machine, it has been a nightmare (and I've been unable to find a working solution one time out of two), but I thought it was mostly because I wasn't aware of how to do things with OS-X... But once you install a different Python than the one by default, you're fine, though. I'd argue that you WOULD install almost all programming languages, so you can do it too with Python, the one that come with OS-X is just a shortcut for quick scripting...
Not sure if I understand the issue with PYTHONPATH... It's basically a hack, so I can't see it used except on very specific occasions. For example, on Linux, most modules will be installed (so different locations for each version), semi-installed (declared among the modules but not stored into site-packages, same result), or stored in .local/lib/python-version/sites-packages (and again, no chance of version clash).
For example:
Code:
$ echo "print 'py2'" > .local/lib/python2.7/site-packages/mytest.py
$ echo "print('py3k')" > .local/lib/python3.4/site-packages/mytest.py
$ python -c "import mytest"
py2
$ python3 -c "import mytest"
py3k
It's basically the same on Windows, but it depends on the distribution, so... (well, on Linux too, but I was talking about the one in repositories)
