Use pew, not virtualenvwrapper, for Python virtualenvs

Tuesday January 20, 2015

Have you noticed how good The Hitchhiker’s Guide to Python is? The documentation there on virtualenv is exemplary.

Of course nobody wants to use virtualenvs directly, which is why virtualenvwrapper exists. But as Lamb pointed out, Virtualenv's bin/activate is Doing It Wrong, and virtualenvwrapper doesn't do it right either. Also, it's annoying to run env'ed Python via cron.

The solution is to use pew instead. The Python Environment Wrapper (pew) handles your environment elegantly. This includes not mangling your PS1, though you can still display VIRTUAL_ENV information in your prompt if you want, and however you want. Also, suddenly all your virtualenv tasks are pew sub-commands, which means all you have to remember is pew. Typing pew alone shows all the pew commands, with helpful descriptions.

I no longer set the WORKON_HOME environment variable. This means pew will use the default ~/.local/share/virtualenvs, which is a good choice. It's consistent with PEP 370, and it means you don't rely on WORKON_HOME to find your virtualenvs, which is nice for cron.

The location of pew is /usr/local/bin. For convenience, I suggest adding a PATH line to your crontab. The default PATH is /usr/bin:/bin, so the following adds one entry:

PATH=/usr/local/bin:/usr/bin:/bin

With that done, you can easily run any Python script you want in any virtualenv you want, via cron, with concise syntax:

* * * * * pew in my_env my_script.py

The example assumes my_script.py is in your home directory, executable, and with the standard #!/usr/bin/env python shebang.

I find this to be a very nice setup: pew workon my_env and develop my_script.py however I want, and pew in my_env my_script.py to run in that virtualenv from cron or anywhere else.

Related tools: virtualenv, virtualenvwrapper, vex, direnv, probably more...

Thanks to Jessica, Rami, and Francis for thoughts on this.