• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

This fixes #192626 (comment), which was noticed when adding python 3.13 last year and now again with 3.14 in #245931

Our sitecustomize.py on Linux is not replacing Cellar paths with their opt equivalent:

Before (note no change to sys.prefix nor sys.base_prefix):

# Without sitecustomize.py
$ python3 -Sc 'import sys; print(f"{sys.executable=}\n{sys.prefix=}\n{sys.base_prefix=}")'
sys.executable='/home/linuxbrew/.linuxbrew/bin/python3'
sys.prefix='/home/linuxbrew/.linuxbrew/Cellar/python@3.13/3.13.7'
sys.base_prefix='/home/linuxbrew/.linuxbrew/Cellar/python@3.13/3.13.7'

# With sitecustomize.py
$ python3 -c 'import sys; print(f"{sys.executable=}\n{sys.prefix=}\n{sys.base_prefix=}")'
sys.executable='/home/linuxbrew/.linuxbrew/opt/python@3.13/bin/python3.13'
sys.prefix='/home/linuxbrew/.linuxbrew/Cellar/python@3.13/3.13.7'
sys.base_prefix='/home/linuxbrew/.linuxbrew/Cellar/python@3.13/3.13.7'

After:

$ python3 -c 'import sys; print(f"{sys.executable=}\n{sys.prefix=}\n{sys.base_prefix=}")'
sys.executable='/home/linuxbrew/.linuxbrew/opt/python@3.13/bin/python3.13'
sys.prefix='/home/linuxbrew/.linuxbrew/opt/python@3.13'
sys.base_prefix='/home/linuxbrew/.linuxbrew/opt/python@3.13'

Looks like @cho-m had already discovered this in #102295 but went stale