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, b

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The virtualenv docs for it are out of date for Python 3 (they claim you use execfile, which doesn't exist).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

Answer 2

import argparse
import base64
import os
import zlib
from pathlib import Path


def convert(s):
    b = base64.b64decode(s.encode('ascii'))
    return zlib.decompress(b).decode('utf-8')


ACTIVATE_THIS = convert("""
eJyNU01v2zAMvetXEB4K21jnDOstQA4dMGCHbeihlyEIDMWmE62yJEiKE//7kXKdpEWLzYBt8evx
kRSzLPs6wiEoswM8YdMpjUXcq1Dz6RZa1cSiTkJdr86GsoTRHuCotBayiWqQEYGtMCgfD1KjGYBe
5a3p0cRKiEe2NtLAFikftnDco0ko/SFEVgEZ8aRCZDIPY9xbA8pE9M4jfW/B2CjiHq9zbJVZuOQq
siwTIvpxKYCembPAU4Muwi/Z4zfvrZ/MXipKeB8C+qisSZYiWfjJfs+0/MFMdWn1hJcO5U7G/SLa
xVx8zU6VG/PXLXvfsyyzUqjeWR8hjGE+2iCE1W1tQ82hsCJN9dzKaoexyB/uH79TnjwvxcW0ntSb
yZ8jq1Z5Q1UXsyy3gf9nbjTEj7NzQMfCJa/YSmrQ+2D/BqfiOi6sclrGzvoeVivIj8rcfcmnIQRF
7XCyeZI7DFe5/lhlCs5PRf5QW66VXT/NrlQ46oD/D6InkOmi3IQcbhKxAX2g4a+Xd5s3UtCtG2py
m8eg6WYWqR6SL5OjKMGfSrYt/6kxxQtOpeAgj1LXBNmpE2ElmCSIy5H0zFd8gJ924HWijWhb2hRC
6wNEm1QdDZtuSZcEprIUBo/XRNcbQe1OUbQ/r3hPTaPJJDNtFLu8KHV5XoNr3Eo6h6YtOKw8e8yw
VF5PnJ+ts3a9/Mz38RpG/AUSzYUW
""")


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('--virtualenv-dir', default=os.environ['VIRTUAL_ENV'])

    args = parser.parse_args()

    activate_this_path = Path(args.virtualenv_dir) / 'bin/activate_this.py'

    print(f'Writing activate_this.py to {activate_this_path}')
    with open(activate_this_path, 'w') as fp:
        fp.write(ACTIVATE_THIS)

I took this from the virtualenv project itself. here search for ACTIVATE_THIS

The script will write an activate_this.py to your virtual environment bin.

With poetry you can do:

poetry run python venv_activate_this.py

For python venv do:

source venv/bin/activate
python venv_activate_this.py

And from anywhere you could do:

python3 venv_activate_this.py --virtualenv-dir /wherever/that/is

Now you can use vim with python and make it understand how to activate the correct virtual environment for things like ALE and YCM.

Also stored as a gist here: https://gist.github.com/nackjicholson/db83869b7931b0bc95fa9e0960921f1c

Answer 3

I used a different approach used in virtualenv itself:

# the current Python interpreter is not from the virtual environment
file = __file__
if file.endswith('.pyc'):
    file = file[:-1]
venv_executable = PROJECT_DIR / 'venv' / 'bin' / 'python'
popen = subprocess.Popen([venv_executable, file] + sys.argv[1:])
raise SystemExit(popen.wait())