gh-60402: Fix Tab in a string in IDLE

[serhiy-storchaka]

Tab after text in a string, as in a docstring, opened the file name completion list with unrelated names. Open it only if some file name starts with the text before the cursor; otherwise insert a tab. Control-Space still opens the list.

🤖 Generated with Claude Code

• Issue: IDLE - tabbing in a string sometimes brings up word completion window #60402

[terryjreedy]

Manual testing with tab in string: no match, no box. If one wants a box, force it.
Box is such a nuisance I am willing to call this a bug fix with no discussion needed.

An unwanted match is still a nuisance, whether one gets completion or box.
One must type a fake no-match entry, tab, and correct the entry, or enter '\t',
or do entry in an empty directory. Fortunately, this should be rare in IDLE use.

Alternative is to disable filename completion with tab, which would need discussion, and which would likely be rejected as more needed than literal tab insertion in situations where IDLE is used.

[miss-islington-app]

Thanks @serhiy-storchaka for the PR, and @terryjreedy for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15.
🐍🍒⛏🤖

[bedevere-app]

GH-157630 is a backport of this pull request to the 3.15 branch.

[bedevere-app]

GH-157631 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-157632 is a backport of this pull request to the 3.13 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 Windows Non-Debug 3.13 (tier-2) has failed when building commit e396482.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/2006/builds/361) and take a look at the build logs.
4. Check if the failure is related to this commit (e396482) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/2006/builds/361

Failed tests:

• test_int

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "C:\Users\buildworker\buildarea\3.13.ware-win11-arm64.nondebug\build\Lib\test\test_int.py", line 740, in test_denial_of_service_prevented_str_to_int
    self.assertLessEqual(sw_fail_extra_huge.seconds, sw_convert.seconds/2)
    ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 0.015625 not less than or equal to 0.0078125