Python 3.13.0b1 REPL does not deduplicate history entries

[hroncok]

Bug report

Bug description:

Consider this:

>>> 1
1
>>> 2
2
>>> 2
2
>>> 2
2
>>> 2
2
>>> 2
2
>>> 2
2
>>>

Now press the arrow up (↑). 2 appears. Then, press it again...

• On Python 3.12, I get 1 after the second ↑ press. I consider this the natural behavior.
• On Python 3.13, I get 1 only after the 7nd ↑ press. I consider this weird.

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-119033: Deduplicate history entries in new REPL #119276

[terryjreedy]

I just discovered that IDLE's history mechanism, which I have not touched, deduplicates history, and/but? omits single char numbers. I would guess the latter is because retyping a single char is as easy as recalling it.

[hroncok]

The single-character example here is just an illustration, this happens with longer lines as well.