Feature or enhancement

Add special handling for-X importtime=2 that provides additional output when already-loaded modules are imported. This will allow users to get a complete picture of runtime imports.

Pitch

While-X importtime is incredibly useful for analyzing module import times, by design, it doesn't log anything if an imported module has already been loaded.-X importtime=2 would provide additional output for every module that's already been loaded:

>>> import uuidimport time: cached    | cached     |   _ioimport time: cached    | cached     |   _ioimport time: cached    | cached     |   osimport time: cached    | cached     |   sysimport time: cached    | cached     |   enumimport time: cached    | cached     |     _ioimport time: cached    | cached     |     _ioimport time: cached    | cached     |     collectionsimport time: cached    | cached     |     osimport time: cached    | cached     |     reimport time: cached    | cached     |     sysimport time: cached    | cached     |     functoolsimport time: cached    | cached     |     itertoolsimport time:       151 |        151 |     _wmiimport time:     18290 |      18440 |   platformimport time:       372 |        372 |   _uuidimport time:     10955 |      29766 | uuid

In codebases with convoluted/poorly managed import graphs (and consequently, workloads that suffer from long import times), the ability to record all paths to an expensive dependency–not just the first-imported–can help expedite refactoring (and help scale identification of this type of issue). More generally, this flag would provide a more efficient path to tracking runtime dependencies.

The changes required are largely unintrusive: here's my reference implementation: [will relink, need to do some paperwork].

Previous discussion

Discussion:https://discuss.python.org/t/x-importtrace-to-supplement-x-importtime-for-loaded-modules/23882/5
Prior email chain:https://mail.python.org/archives/list/python-ideas@python.org/thread/GEISYQ5BXWGKT33RWF77EOSOMMMFUBUS/

Linked PRs

• gh-102567: Add -X importtime=2 for logging an importtime message for already-loaded modules #118655
• gh-102567: Add -X importtime=2 for logging an importtime message for already-loaded modules #133443