Python dependencies not installing in 2.7 and 3.7

[futuregerald]

Currently builds with a requirements.txt are failing due to permissions errors while installing Python dependencies. This appears to be a regression from a recent release. The error that's shown in the build log is:

Permission denied: '/lib/python3.7'

It is happening in both Python 2.7 and 3.7. An example of a failing build is: https://app.netlify.com/sites/sharp-noyce-c7bf26/deploys/5cc8a5bc378b41e554cf579f

The repo it happened on is public so I cloned it to
https://github.com/futuregerald/istevens.com/tree/staging

To be clear, it's happening on staging.

The runtime.txt contains:
3.7
(though they tested with 2.7 and had a similar experience)

The requirements.txt contains:
lektor

cc @bcomnes

[bcomnes]

Addressing this 🔥today

[bcomnes]

@futuregerald Could this be one of the scenarios we need to set up a virtualenv? https://www.netlify.com/docs/#python

We haven't switched to pipenv yet unfortunately.

[futuregerald]

It's possible. I don't use Python so I have no expertise in this area.

[istevens]

Sorry to jump in, but it appears as though build-image is already creating Python virtualenvs in /opt/buildhome on instantiation, and activating the right one before the build.

I can't be certain why pip is trying to install packages to /lib and not /opt/buildhome. However, if I explicitly call the correct pip from the build image, subsequently calling the build command works, eg. (with a runtime.txt of 3.6):

> build lektor build --output-path ./build
[…]
Error installing pip dependencies
> /opt/buildhome/python3.6/bin/pip3 install lektor
[…]
Successfully installed […]
> build lektor build --output-path ./build
[…]
Finished build in 4.21 sec

[bcomnes]

@istevens Interesting, I wonder if its its not activating correctly. Thank you for the datapoint.

[istevens]

After isolating the pip error to a few build commands, I found it was a setup.cfg in my repo causing the issue. I added it to address an error when building an Atom feed, and assumed it would only take if my project was explicitly installed. Turns out, pip was using setup.cfg when run from the project dir to install dependencies.

The setup.cfg content in question:

[install]
prefix=

[PerrySetGo]

if any work happens on this please update the following community thread: https://community.netlify.com/t/permission-denied-lib-python2-7-installing-python-packages-worked-for-weeks/638/4