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GeezerVison is showing github.com — gh-156363: Speed up import of rlcompleter by deferring inspect and re by maxday · Pull Request #156364 · python/cpython

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@maxday

@maxday maxday commented Aug 25, 2026 •
edited by bedevere-app Bot
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Speed up import of rlcompleter by deferring inspect and re
Defer the imports of inspect and re in rlcompleter into the methods that actually use them (_callable_postfix and attr_matches).

Impact
On a local build, importing rlcompleter dropped from ~16.4 ms to ~1.8 ms of cumulative import time.

Measured with:

python -X importtime -c "import rlcompleter"

Test
A regression test using test.support.import_helper.ensure_lazy_imports guards that inspect and re are not imported as a side effect of importing rlcompleter.

Fixes: #156363

  • Issue: Speed up import rlcompleter by deferring inspect and re #156363

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@maxday
pythongh-156363: Speed up import of rlcompleter by deferring inspect …
fadfaf9 
…and re

rlcompleter imported inspect and re at module scope, but each is used in
exactly one completion method (inspect in Completer._callable_postfix, re
in Completer.attr_matches).  Neither is needed to construct a Completer or
set up interactive completion, only to compute completions.

inspect in particular is a heavy import (it pulls in dis, tokenize, ...),
so importing rlcompleter dropped from ~16.4ms to ~1.8ms of cumulative
import time on a local build.  Defer both imports into the methods that use
them and add a lazy-import guard test.
@bedevere-app bedevere-app Bot mentioned this pull request Aug 25, 2026
Speed up import rlcompleter by deferring inspect and re #156363
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@bedevere-app bedevere-app Bot added the awaiting review label Aug 25, 2026
@maxday

maxday commented Aug 25, 2026

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I believe the macOS failing test can be rerun, looks like it's a network error issue, from the log: "The hosted runner lost communication with the server. Anything in your workflow that terminates the runner process, starves it for CPU/Memory, or blocks its network access can cause this error."
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@aisk

aisk commented Aug 25, 2026 •
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If we decide to do this, we can use the lazy import syntax introduced in https://peps.python.org/pep-0810/ to resolve it.
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hugovk
hugovk reviewed Aug 25, 2026
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Comment thread Lib/rlcompleter.py Resolved

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@maxday
pythongh-156363: Use PEP 810 lazy imports for inspect and re in rlcom…
0ba9e10 
…pleter

Address review feedback: replace deferred in-function imports of
`inspect` and `re` with `lazy import` statements at the top of the
module, keeping them alongside the regular imports.
@maxday
maxday requested a review from hugovk August 25, 2026 17:50
StanFromIreland
StanFromIreland reviewed Aug 25, 2026
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Comment thread Lib/rlcompleter.py Outdated
import __main__
import warnings
import types

@StanFromIreland StanFromIreland Aug 25, 2026

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Suggested change

lazy imports shouldn't be separate.

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StanFromIreland
StanFromIreland reviewed Aug 25, 2026
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Comment thread Misc/NEWS.d/next/Library/2026-08-25-12-43-10.gh-issue-156363.RlzImp.rst Outdated
Comment on lines +1 to +5
Speed up ``import rlcompleter`` by deferring the imports of :mod:`inspect`
and :mod:`re` into the completion methods that use them. They are only
needed while computing completions, so importing :mod:`rlcompleter` (for
example when setting up interactive completion) no longer pays their import
cost.

@StanFromIreland StanFromIreland Aug 25, 2026

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Suggested change
Speed up ``import rlcompleter`` by deferring the imports of :mod:`inspect`
and :mod:`re` into the completion methods that use them. They are only
needed while computing completions, so importing :mod:`rlcompleter` (for
example when setting up interactive completion) no longer pays their import
cost.
Speed up the :mod:`rlcompleter` module's import time.

The rest is implementation details.

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@maxday
pythongh-156363: Use PEP 810 lazy imports for inspect and re in rlcom…
a79e157 
…pleter

Address review feedback
@maxday

maxday commented Aug 26, 2026

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Thanks for the review @StanFromIreland I've addressed both of your comments :)
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@maxday
maxday requested a review from StanFromIreland August 26, 2026 11:44
StanFromIreland
StanFromIreland reviewed Aug 26, 2026
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Comment thread Misc/NEWS.d/next/Library/2026-08-25-12-43-10.gh-issue-156363.RlzImp.rst Resolved

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@python-cla-bot

python-cla-bot Bot commented Aug 26, 2026 •
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All commit authors signed the Contributor License Agreement.

CLA signed
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@maxday @StanFromIreland
Update Misc/NEWS.d/next/Library/2026-08-25-12-43-10.gh-issue-156363.R…
fd0a08f 
…lzImp.rst

Co-authored-by: Stan Ulbrych <[email protected]>
@maxday
maxday force-pushed the maxday/speedup-rlcompleter-lazy-imports branch from 95578c1 to fd0a08f Compare August 26, 2026 16:12
@aisk

aisk commented Aug 26, 2026 •
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Hi @maxday, please avoid force push in the future, see https://devguide.python.org/getting-started/pull-request-lifecycle/#don-t-force-push

And for the reviewers, I made a comment on the original issue: #156363 (comment):

One thing to notice, on the interactive startup path these two modules get imported a moment later anyway, since _pyrepl.readline is imported right after rlcompleter and pulls them both in:

$ ./python -c "import sys, _pyrepl.readline; print('re' in sys.modules, 'inspect' in sys.modules)"
True True

So the gain doesn't really materialize for the interactive interpreter. It may still help people who use this module on its own, though.
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@maxday

maxday commented Aug 26, 2026 •
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Sorry @aisk I didn't know, I won't do it again for sure :) thanks for the link
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@maxday
maxday requested a review from StanFromIreland August 27, 2026 14:54
@StanFromIreland

StanFromIreland commented Oct 22, 2026

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I'm going to close, this does not seem worth it to me. If another core developer wishes to take this on, I won't block.
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@StanFromIreland StanFromIreland closed this Oct 22, 2026
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@hugovk hugovk Awaiting requested review from hugovk
@StanFromIreland StanFromIreland Awaiting requested review from StanFromIreland

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Speed up import rlcompleter by deferring inspect and re

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@maxday @aisk @StanFromIreland @hugovk
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