site module missing PREFIXES attribute

[k-dominik]

Hi!

while trying to package an app with the latest dask version, I found that dask will try to access site.PREFIXES (relevant python docs, dask PR that introduces the access).

The site module provided by py2app currently doesn't contain this attribute.

Naively I would say that adding something along the lines of cpython site should do the trick? (Meaning I tried it locally and it worked, however, I am not sure that all cases that might occur are covered by that)

# from cpython Lib/site.py

# Prefixes for site-packages; add additional prefixes like /usr/local here
PREFIXES = [sys.prefix, sys.exec_prefix]

Happy to open a PR along these lines if you agree that this is the way to go.

Cheers