optimize getting of line number in pytest discovery#26017
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…xpensive call before falling back to location query
eleanorjboyd
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Pull request overview
This PR speeds up pytest test discovery by avoiding the expensive pytest.Item.location path computation when only the line number is needed, using pytest’s internal Code.from_function(...).firstlineno as a fast-path with a fallback to the public API.
Changes:
- Use
_pytest._code.code.Code.from_function(...).firstlinenoto obtain the test item’s line number without computing the path. - Add a fallback to
test_case.location[1]when the internal API cannot be used.
Show a summary per file
| File | Description |
|---|---|
| python_files/vscode_pytest/init.py | Optimizes line-number retrieval during pytest discovery by using an internal pytest API fast-path with fallback. |
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- Files reviewed: 1/1 changed files
- Comments generated: 2
- Review effort level: Low
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| import pytest | ||
| from _pytest.python import PyobjMixin | ||
| from _pytest._code.code import Code |
| # Before falling back to that high-level API, we try to use | ||
| # internal API to get just line number without the path. | ||
| lineno0 = Code.from_function(cast(PyobjMixin, test_case).obj).firstlineno | ||
| except: |
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The discovery for pytest is still quite a bit slower than running plain
-m pytest --collect-onlyso I investigated a bit more and the next most significant (at least for our test suite) slowdown is caused by thepytest.Item.locationcall used to get line number of the test:This is because the
.locationreturns tuple of path and line number, of which only the line number is used by the discovery, but computing the path is rather expensive. This PR proposes an optimization which uses internal pytest API in exactly the same way as thelocationfunction itself, but without also computing the path.In particular, the
locationcall hierarchy is:This PR calls
Code.from_functiondirectly and only gets.firstlinenofrom it.Both profiles are captured with this PR cherry-picked to main branch prior to the discovery result compaction introduced in 5389068 which causes significant performance hit that overshadows the optimization done here, for that I created a separate PR #26016 with proposed fix.
This change makes the discovery about 20% faster for our suite, now almost on par with the raw
pytestcall