Description

tanloong

opened on Mar 1, 2026

Issue body actions

Bug report

Bug description:

The current completion logic in Lib/_pyrepl/completing_reader.py uses a suffix-insertion strategy (source code):

In the contrast, Readline completely replaces user input with the candidate (source code).

This will lead to unwanted behavior in case-insensitive completion scenario. If user input 'xy', they might get 'xyZZY' instead of the expected 'XYZZY'.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-145392: Fix _pyrepl completion to replace input stem instead of appending #145393

Activity

1. tanloong

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Mar 1, 2026
2. picnixz

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   topic-replRelated to the interactive shellRelated to the interactive shell

   on Mar 1, 2026
3. tanloong

   changed the title [-]PyREPL: Different Completion Behavior Between with GNU Readline[/-] [+]PyREPL: Different Completion Behavior with GNU Readline[/+] on Mar 5, 2026
4. encukou commented on Apr 1, 2026

   

   encukou

   on Apr 1, 2026

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   Do you have a reproducer?
   Is this needed/helpful for SQLite?
5. tanloong commented on Apr 1, 2026

   

   tanloong

   on Apr 1, 2026

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   Yes, this will be helpful for SQLite.

   After seeing #145379, I wondered if the SQLite CLI could also use PyREPL. That would greatly improve the experience on Windows. I had an LLM create a quick demo of the SQLite CLI using PyREPL.

   In that demo, when I type sel and press Tab, it completes to selECT instead of the correct SELECT.
   I will push the demo branch as a reproducer soon.

   The demo is far from ready-to-use, and there are also syntax highlighting issues (maybe could not solved until #141619 is merged). But I believe the SQLite CLI will eventually move to PyREPL (we might not need to modify the sqlite module directly but instead update the underlying code module to use PyREPL). Changing the completion to use a replace-strategy instead of suffix-insertion will help with this. I'm fine with pausing this issue until the SQLite CLI moves to PyREPL, and then treat it as a SQLite bug only after that.
6. tanloong commented on Apr 1, 2026

   

   tanloong

   on Apr 1, 2026

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   This is the demo branch as a reproducer: https://github.com/tanloong/cpython/tree/sqlite-pyrepl

   In the screen recording, when typing sel and press Tab, it completes to selECT instead of SELECT.

   simplescreenrecorder-2026-04-01_21.46.35.mp4
7. encukou commented on Apr 7, 2026

   

   encukou

   on Apr 7, 2026

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   Thanks! That makes sense.

   I'm fine with pausing this issue until the SQLite CLI moves to PyREPL, and then treat it as a SQLite bug only after that.

   Let's do that. There is no issue in current use of pyrepl, and if sqlite3 starts using it, it'll only be a small inconvenience.

   Reacted by Tan Long
8. encukou

   added

   type-featureA feature request or enhancementA feature request or enhancement

   and removed

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Apr 8, 2026
9. encukou commented on Apr 8, 2026

   

   encukou

   on Apr 8, 2026

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   I'll close for now; let's reopen when this becomes helpful.
10. encukou

    closed this as not plannedon Apr 8, 2026

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