Description of problem:
After the Python 3.15 update in Rawhide every interpreter startup prints a traceback from the legacy google-namespace .pth file shipped in python3-protobuf3:

Error in import line from /usr/lib/python3.15/site-packages/protobuf-3.19.6-py3.15-nspkg.pth: import sys, types, os;p = os.path.join(sys._getframe(1).f_locals['sitedir'], *('google',));importlib = __import__('importlib.util');__import__('importlib.machinery');m = sys.modules.setdefault('google', importlib.util.module_from_spec(importlib.machinery.PathFinder.find_spec('google', [os.path.dirname(p)])));m = m or sys.modules.setdefault('google', types.ModuleType('google'));mp = (m or []) and m.__dict__.setdefault('__path__',[]);(p not in mp) and mp.append(p)
  Traceback (most recent call last):
    File "<frozen site>", line 533, in _exec_imports
    File "<string>", line 1, in <module>
  KeyError: "local variable ''sitedir'' is not defined"

The line is setuptools' pkg_resources-namespace stub; it gets the site dir via sys._getframe(1).f_locals['sitedir']. Through 3.14 site.addpackage(sitedir, ...) ran the line itself, so frame 1 was addpackage and 'sitedir' was its parameter. 3.15 rewrote site.py (PEP 829, gh-148641/gh-150228) and import lines now run inside StartupState._exec_imports(), which has no 'sitedir', hence the KeyError. The "local variable ... is not defined" text is the PEP 667 fast-locals-proxy KeyError from 3.13.

It's non-fatal, site.py catches it and continues, but it prints at every python3 startup including from scriptlets that run python3. I first saw it in the fedora-third-party triggers, but those complete fine and it isn't specific to them. Import lines in .pth are deprecated by PEP 829 and the stub depends on a private site internal that was never guaranteed, so the fix belongs in the package, not CPython.

Version-Release number of selected component (if applicable):
protobuf3-3.19.6-64.fc45
python3-3.15.0~b2-2.fc45

How reproducible:
Always

Steps to Reproduce:
1. Rawhide with python3-3.15.0~b2 and python3-protobuf3 installed
2. python3 -c ''

Actual results:
A traceback on stderr at every startup (Error in import line ... KeyError ...'sitedir'...).

Expected results:
No output.

Additional info:
Fix: drop the legacy namespace_packages and ship as a PEP 420 native namespace (no *-nspkg.pth generated). Afterwards python3 -c '' is silent and import google.protobuf still works. The google namespace is shared with other packages (google-api-*, grpcio, ...), so check that it still resolves across all co-installed providers after the switch.
Refs: gh-148641, gh-150228 (Barry Warsaw); What's New in Python 3.15, site.StartupState.

Reproducible: Always