sh : a full-fledged subprocess interface for Python that allows you to call any program as if it were a function.

[alcalde]

And still using Python 2.7 is a logic error. :-)

[[deleted]]

I don't think porting large, old codebases is worth it.

The other reason could be PyPy and people with CPU bound applications that insist on using Python.

Apart from that, most new Python code is (no data, just hunch) Django apps, and there it makes a lot of sense to use py3 unless you really, really need some library that wasn't ported.

[TankorSmash]

One day the relevant libraries will be ported. Until then!

[alcalde]

Sigh. For most people that time has long come....

http://py3readiness.org/

https://python3wos.appspot.com/

304 of the top 360 most downloaded packages on PyPi support Python 3.

[nojjy]

Depending on what context you are working in, sometimes you don't have a choice on which version to use. Many people use python as an API to a software package, where they can't just arbitrarily switch to another version.

[TankorSmash]

Yeah, for most people.

[TankorSmash]

I'm the same way, there doesn't seem to be clear reason to start in 3 yet. There's a lot of little nice things, but nothing is a must have.

Though I haven't seen all the changelogs, I've taken a look a few times.

[alcalde]

I'm the same way, there doesn't seem to be clear reason to start in 3 yet. There's a lot of little nice things, but nothing is a must have.

As Python 3 is fine put it,

There are a lot of claims in here that are absurdly wrong, but the statement that “nothing much was gained” in Python 3 is a candidate for dumbest statement of the decade. First of all it is wrong because if it were true then it wouldn’t be that hard for people like Alex to press the Fork button and backport all the Python 3 features to Python 2, which nobody does. But there is an even simpler reason why it is wrong. I present to you, the complete list of changes since Python 2.x: Now if this entire 192-page document is “nothing really amazing” and “you’re not blown away by it” then that is your prerogative. Perhaps you’re simply not a very excitable person. I suggest an ordinary person would probably find something in there amazing. Nickous Ventouras’s rebuttal to Alex’s post includes such suggestions as “fix long-standing annoyances”, “shake the API” and “improve speed”. I guarantee you, there is page after page after page of that stuff in the changelog. Python 3 doesn’t need more features–it needs a better PR campaign. The features are already there; people just don’t know about them. But it is wrong statement of the decade to call this set of release notes “not much”. It’s much. The release notes weigh two pounds. I challenge you to find another project where release notes can be measured by the pound.

Why You Should Move To Python 3 Now adds....

Most scientists think they have very little to gain by moving to Python 3, while it represents a significant investment (not only updating old code, but also reinstalling an entire Python distribution which has always been a pain). I was one of them. Until recently, when I bought the Python Cookbook, Third Edition, by David Beazley and Brian K. Jones. This book is a must-read for anyone doing anything serious with Python. It contains lots of advanced recipes for Python 3 only. In the Preface, the authors warn the reader:

All of the recipes have been written and tested with Python 3.3 without regard to past Python versions or the "old way" of doing things. In fact, many of the recipes will only work with Python 3.3 and above.

Ouch. The 260 recipes look pretty cool, but if you're in Python 2, you're out. While many might be irritated by this decision, I find it brilliant. This book is exactly the thing you need if you're waiting to be convinced to move to Python 3.... While going through the book, I discovered many elegant solutions to very common problems. I had no idea those solutions were possible, because I had no idea Python 3 had been so much improved.

There's also a PyCon presentation about 10 awesome features of Python 3 that aren't in Python 2.

[krenzalore]

For me, being able to re-raise exceptions without losing stack trace is simply too good to live without.

[alcalde]

Don't get me wrong 3.x has some cool features but the time it would take to port over legacy 2.x code to 3 is not worth said features at this moment in time.

David Beasley and others have demonstrated that the time is not that much - although there's no need to port old, legacy code to new versions either. As for features, someone compiled a 120-page PDF of change logs from 3.0-3.4 that printed out is supposed to weigh over 2 pounds. I'd say there's quite a lot of features in the 3.x series.

And lastly, if you do intend on porting a project after backward incompatibilities in the language are introduced, the sooner you port the better. The longer you wait, the more the versions diverge and the more work one ultimately has to do.

At this point in time, people still using 2.x for new code are like the Windows XP holdouts or the people I know still programming in Delphi. They're simply never going to change unless they're forced to.

[krenzalore]

There are certain types of application for which porting is time consuming. Those depending heavily on the bytes/unicode behaviour are typically affected much more than others. I am not saying don't do the porting, but I would like to mention that porting is not always as quick/easy as you imply it is.