IDLE: Performance Issue with Long Lines Due to Quadratic Complexity

[kexinoh]

Bug report

Bug description:

Bug Description:
A series of performance issues related to quadratic complexity has been identified in IDLE's editor. On files with very long lines, this can cause the editor to freeze or hang.

Vulnerability Locations:

• 1 (Fixed): https://github.com/python/cpython/blob/5ab66a882d1b5e44ec50b25df116ab209d65863f/Lib/idlelib/editor.py#L1206
• 2 (Not need fix): https://github.com/python/cpython/blob/5ab66a882d1b5e44ec50b25df116ab209d65863f/Lib/idlelib/editor.py#L1373

Repair Status:

• Issues 1 have been fixed by @johnzhou721.
• gh-136061: IDLE - update code in editor.Editor.load_extension #134874

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-136061: IDLE - update code in editor.Editor.load_extension #134874

[johnzhou721]

@kexinoh Bug 2 is invalid because "anyone who can edit files or get code files loaded can do much worse than than make IDLE hang on hitting" (Reedy 2025).

In addition:

Any such [refactoring] project [of the block of code in bug 2] must begin with a separate issue and an detailed analysis of current versus desired behavior, and it must consider the entire block of relevant code. This is lines 1365-1385, which begin with the comment

It may require inserting spaces if we back up over a tab character! This is written to be clear, not fast.

REFERENCES
#134874

[kexinoh]

I modified the content about this part in the issue

[johnzhou721]

@kexinoh Thanks!