fix(python): remove redundant debug setter call in __deepcopy__

[markjm]

Hi! It seems I'm hitting an extremely pathological case during the creation of many openapi-generated objects in a very large (many registered loggers) codebase.

The __deepcopy__ method on the Configuration copies all __dict__ items (including _Configuration__debug) and then loggers are shallow-copied over. After that, we call result.debug = self.debug which fires the property setter with the same value already present. On Python 3.12+ (actually maybe earlier, just what im using here) , the setter's logger.setLevel() call triggers logging.Manager._clear_cache() which iterates every registered logger — O(n_loggers) per deepcopy.

In applications with many loggers, this causes severe performance degradation when Configuration objects are deepcopied frequently (e.g., per-request in API clients).

I let my friendly bot create an example perf bechmmark to showcase the issue and fix:
https://gist.github.com/markjm/bb5805505d9dfddc5d595cadd0beaff1

$ python3 scripts/python_debug_setter_repro.py
Python 3.12.3
Registered loggers: 20,000
deepcopy() calls:   1,000

  Before fix: 1.744s
  After fix:  0.004s
  Speedup:    413.2x

The redundant debug setter in deepcopy causes measurable overhead that scales with the number of registered loggers (O(n_loggers) per copy).

Because we already copy over the parts we want (and explicitly configure loggers how we want on copy), I believe this change to be essentially a noop except for the perf improvement.

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---

Summary by cubic

Remove a redundant debug setter call in Python clients’ Configuration.__deepcopy__. This avoids O(n_loggers) logger cache clears on Python 3.12+ and significantly speeds up deepcopy in apps with many loggers.

• Bug Fixes
  • Stop calling result.debug = self.debug in __deepcopy__; the value is already copied from __dict__.
  • Keep the logger_file setter to re-create the file handler excluded from the dict copy.
  • Update Python templates and regenerated samples; add tests ensuring deepcopy preserves debug True/False.

^{Written for commit b83efd1. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 13 files

_{Re-trigger cubic}

[wing328]

thanks for the PR

can you please review the CI test failures when you've time?

[markjm]

would you mind triggering them one more time? the error looks to be when hitting live https://petstore.swagger.io/ which it seems may have not been bahving during those tests. i can not repro locally

[wing328]

the error looks to be when hitting live https://petstore.swagger.io/

it shouldnt be the case as it should be hitting the petstore server running locally but looks like my assumption is wrong as restarting it did fix the issue.

i'll take another look later as we don't want to use the public petstore server (not owned by us)

thanks for your contribution.

(https://github.com/OpenAPITools/openapi-generator/actions/runs/27038354307/job/80237543724?pr=23958 not related tot his change)