[TIP] Tox and setup.py enforcing python version

[Florian Bruhin]

* Roy Wright <roy at wright.org> [2015-06-02 14:14:54 -0500]:
> Howdy,
> 
> For my python3 apps I've been including the following to prevent them from being installed on python2:
> 
> import sys
> if sys.version_info < (3, 3):
>     print("appname requires python 3.3 or newer")
>     exit(-1)
> 
> Now my system python is 2.7 (Ubuntu 14.04) so running tox will immediately fail even with:
> 
> [tox]
> envlist = py33,py34
> 
> Removing the exit allows tox to run. 

Where did you add that? I guess to setup.py?

> I'm just curious what is the best practice here?  Run tox from python3 virtualenv? Let the user beware? Depend on classifiers?

Being compatible with python3 only means you make life harder for
contributors who are used to just being able to run 'tox'.

I have some similar check, but at runtime[1]. This means installing
will work, but at least when running it the user gets a clear error.

Of course, this file must be python2 compatible, and everything
imported/run before it at least not be a SyntaxError.

[1] https://github.com/The-Compiler/qutebrowser/blob/master/qutebrowser/misc/checkpyver.py

Florian

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