How can I activate a pyvenv vitrualenv from within python? (activate_this.py was removed?)

Question

I'm using Python 3.4, and having created a pyvenv, I'm looking to activate it from within a python process. With virtualenv, I used to use activate_this.py, but that appears to be gone in pyvenv.

Is there now an easy way to effectively change the current interpreter to the virtualenv interpreter? I could probably mess around with the PATH (which is what activate_this.py did), but I'd like a simpler and stabler way.

This is for use in a wsgi.py.

Answer 1

pyvenv and the venv module don't support this out of the box. The third party virtualenv package does support this using activate_this.py, but that feature was not included in the built-in venv module.

You could try to borrow a copy of activate_this.py from a virtualenv based environment; it seems to work, though I can't swear it will be perfect (venv/pyvenv uses some magic during startup; unclear if all of it is replicated via activate_this.py).

The virtualenv docs for it are out of date for Python 3 (they claim you use execfile, which doesn't exist). The Python 3 compatible alternative would be:

activator = 'some/path/to/activate_this.py'  # Looted from virtualenv; should not require modification, since it's defined relatively with open(activator) as f:     exec(f.read(), {'__file__': activator}) 

Nothing activate_this.py does is magical, so you could manually perform the same changes without looting from virtualenv (adjusting PATH, sys.path, sys.prefix, etc.), but borrowing makes it much simpler in this case.