[eeZi]

A few reasons which made me switch:

  - Python 2 will be EOL in 2020, that's four years

  - vastly improved Unicode support

  - a number new libraries are Python 3 only

  - asyncio and the new async syntax

  - exception chaining (!)

  - type annotations

  - lots of improvements all over the place

[sandGorgon]

Python 2 will not be EOL in 4 years. Not with the billions of lines of code out there. If the Python foundation dares to do this, it will create a fork. Probably even funded by Dropbox, Google and the like.

I wont dispute you on any other aspects - except two. have you tried using gevent versus asyncio ? gevent is running in production at several of the largest API services in the world. Asyncio is not yet deployed at this scale.

Second about new libraries being python 3 only - really dispute that. In fact its the other way around. For example, the brand new Tensorflow library (which google uses in production for its own AI) was released on Python 2 only .. and Python 3 support was later patched in. This is the case with every new library of consequence that I'm seeing.

[eeZi]

The Python foundation won't budge on the 2020 EOL date, for sure. RedHat will support it until RHEL 7 is EOL (~2027), but that's security/critical fixes only - while Python 3 gets all the new features and development efforts.

At some point, the opportunity cost of staying with Python 2.7 is higher than the one-time effort of porting everything to Python 3, so companies will move. Especially the likes of Google and Dropbox.

gevent vs. asyncio - sure, gevent is more mature. But asyncio is undoubtedly the better/nicer API. asyncio's explicit await syntax is much nicer than gevent's implicit monkey-patching, which makes it harder to reason about the code.

Tensorflow isn't really a new library, it was only recently open sourced.

As for Python 3-only libraries:

- https://pypi.python.org/pypi?:action=browse&show=all&c=595

- https://github.com/aio-libs

Also note that Django will drop Python 2 support in time with the Python 2 EOL: https://www.djangoproject.com/weblog/2015/jun/25/roadmap/

Also, many new Python-based open source projects are Python 3 only.

[takeda]

This is wishful thinking.

There's a cost to maintain, and that's why PSF is moving to 3. I'm sure if Google and/or Dropbox would pay, PSF might continue maintenance[1].

Anyway the issue here is that you won't get any new features in python 2.7, and that already happened last year, currently python 2 only gets security fixes.

> have you tried using gevent versus asyncio ? gevent is running in production at several of the largest API services in the world. Asyncio is not yet deployed at this scale.

Both of them are available on python 3. On python 2 you can't chose. AsyncIO strength is that it is integrated into the language. Especially in 3.5 you have a new syntax to use it, no need to install new libraries, no need to compile anything. No monkey patching. Also AsyncIO is more generalized and could be adapted to other tasks, not necessarily for asynchronous calls.

[1] In fact surely Red Hat will continue to maintain it until 2027 since they decided to ship it with Red Hat 7, but question is whether they will share it with general users, or will they only provide it to paying customers.