I wanted to highlight a couple of environment variables added earlier this year which can give you greater control over your builds — both of which were created by community contributors! 
First, we have PYTHON_VERSION, contributed by GitHub user duckinator, who recognized the benefit of consistency and added a variable for setting a build’s Python runtime in the same way that you can with Ruby or Node.js.
Next, we have NETLIFY_USE_YARN, contributed by GitHub user Embraser01. You can use it to control whether Netlify installs Yarn and uses it to install JavaScript dependencies, regardless of whether you have a yarn.lock file in your site’s base directory.
You can learn more about these variables and build dependency management in the docs:
Hooray for users helping users! It’s a joy and an honor to be a part of the community you all help create. 