[issue41549] IDLE leaks `_` into hint box

[wyz23x2]

New submission from wyz23x2 <wyz23x2 at 163.com>:

Reproduce:
1. Open shell and enter an expression, say 1+1.
2. Create a new file and save.
3. Enter a letter and press Tab. `_` appears in the box.

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assignee: terry.reedy
components: IDLE
messages: 375383
nosy: terry.reedy, wyz23x2
priority: normal
severity: normal
status: open
title: IDLE leaks `_` into hint box
type: behavior
versions: Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41549>
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