Linecache updatecache can perform many useless os calls

[tconley1428]

Bug report

Bug description:

Consider the scenario where updatecache is called with a frozen module and module_globals is None.

In that case, _source_unavailable returns false because it is a frozen module, but because module_globals is None, the code carries on to look for the 'file' <frozen module> everywhere in sys.path. Compare that to the behavior prior to #132662 where that frozen module would simply return unavailable. I would recommend the following change:

 if filename.startswith("<frozen ") and module_globals is not None:
 # This is a frozen module, so we need to use the filename
 # from the module globals.
 fullname = module_globals.get("__file__")
 if fullname is None:
 print("fullname none")
 return []

Into

 if filename.startswith("<frozen "):
 if module_globals is None:
 return []

 # This is a frozen module, so we need to use the filename
 # from the module globals.
 fullname = module_globals.get("__file__")
 if fullname is None:
 print("fullname none")
 return []

For context, this is a problem for us because we run in a sandbox which restricts many OS operations, and this is performing useless os operations where it didn't prior to 3.14.

If there is agreement and it is helpful, happy to contribute a PR for this small change.

CPython versions tested on:

3.14

Operating systems tested on:

macOS, Windows, Linux

Linked PRs

• gh-140228: Linecache source is unavailable for frozen modules when global modules is None #140377
• [3.14] gh-140228: Avoid making unnecessary syscalls in linecache for frozen modules (GH-140377) #140738

[tconley1428]

I would argue that type-bug is appropriate. While in most cases the impact is limited to performance, for our use case the additional filesystem calls cause a failure.

[gaogaotiantian]

I did this PR and I agree this should be changed. Just move the comment to the start of the scope as module_globals check is related. If you want you can make a PR. Otherwise I’ll fix it myself soon.

[StanFromIreland]

Triage: Can this be closed?

[gaogaotiantian]

Thank you for checking it out, closed.