How to get a pre-commit hook to find the needed executable on Mac

[rowen]

I have a git pre-commit hook that formats my Python code using `black` on macOS. It works fine from the command line, but (of course) SourceTree cannot find `black`, so I cannot commit in SourceTree.

Any idea how to work around this? I looked through the SourceTree preferences for the ability to set some relevant path, but didn't find anything.