gh-128388: pyrepl on Windows: add meta and ctrl+arrow keybindings

[paulie4]

Fix Lib/_pyrepl/windows_console.py to support more keybindings, like the Ctrl+← and Ctrl+→ word-skipping keybindings and those with meta (i.e. Alt), e.g. to kill-word or backward-kill-word.

Specifics: if Ctrl is pressed, emit "ctrl left" and "ctrl right" instead of just "left" or "right," and if Meta/Alt is pressed, emit the special key code for meta before emitting the other key that was pressed.

NOTE: this is my first PR for https://github.com/python/cpython, so please tell me if I need to do something else, e.g. does this need an entry added somewhere under Misc/NEWS.d?

• Issue: pyrepl on Windows: add Ctrl+← and Ctrl+→ word-skipping and other keybindings #128388

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[hugovk]

NOTE: this is my first PR for https://github.com/python/cpython, so please tell me if I need to do something else, e.g. does this need an entry added somewhere under Misc/NEWS.d?

Yes please, and also sign the CLA.

[paulie4]

@hugovk, Misc/NEWS.d is a directory, so I don't know which file(s) in there to edit, especially since it looks like the versions in there have all been released. Do I need to create a new file (or files if it's going to both 3.13.2 and to a 3.14.0a)?

UPDATE: it looks like these are the instructions for which file I should create: https://devguide.python.org/core-developers/committing/#how-to-add-a-news-entry. I think _pyrepr is part of the standard library, right?

I tried signing the CLA, but the SIGN IN WITH GITHUB TO AGREE button doesn't work with the @users.noreply.github.com email address I use for my commits. I submitted a manual CLA, so hopefully that will work. FYI, this is the error I get when I try to use https://cpython-clabot.herokuapp.com/contributor-license-agreement?state=...:

Thank you for authorizing our application, but the CLA must be signed by the users who contributed to the PR. Authors emails are: [email protected].

[hugovk]

UPDATE: it looks like these are the instructions for which file I should create: https://devguide.python.org/core-developers/committing/#how-to-add-a-news-entry. I think _pyrepr is part of the standard library, right?

Yes, that's right, the Lib dir is the stdlib.

[paulie4]

@hugovk, thank you for that suggested doc change, which I approved. Is there anything else I need to do, or do we now just need to wait for someone else (e.g. @pablogsal, @lysnikolaou, or @ambv) to review the code changes?

[hugovk]

Thanks for the updates. Yes, someone with Windows will need to review, hopefully it shouldn't be too long :)

[eendebakpt]

I left some comments for improvement of the code, but the PR is good: I tested with Windows 11 and the meta keybindings work now

[eendebakpt]

This makes Alt+← and Ctrl-Alt+← work just as Ctrl+←. Is that how it should be?

On Unix for me Alt+← gives me capital C (not sure why, does not really make sense to me) and Ctrl-Alt+← triggers my window manager.

In the keymap I also don't see Alt-left with a special meaning:

cpython/Lib/_pyrepl/reader.py

Lines 146 to 161 in f157485

	(r"\<up>", "up"),
	(r"\<down>", "down"),
	(r"\<left>", "left"),
	(r"\C-\<left>", "backward-word"),
	(r"\<right>", "right"),
	(r"\C-\<right>", "forward-word"),
	(r"\<delete>", "delete"),
	(r"\x1b[3~", "delete"),
	(r"\<backspace>", "backspace"),
	(r"\M-\<backspace>", "backward-kill-word"),
	(r"\<end>", "end-of-line"), # was 'end'
	(r"\<home>", "beginning-of-line"), # was 'home'
	(r"\<f1>", "help"),
	(r"\<f2>", "show-history"),
	(r"\<f3>", "paste-mode"),
	(r"\EOF", "end"), # the entries in the terminfo database for xterms

[paulie4]

Exactly, I didn't see anything existing that was useful for Alt+←, so I figured might as well make it useful. I can remove it if you prefer only Ctrl+← being useful. Also, it would definitely violate separation of concerns if this Lib/_pyrepl/windows_console.py file were to try to read the keymappings in Lib/_pyrepl/reader.py to check if r"\M-\<left>" existed, and I don't expect that to be added anytime soon.

[eendebakpt]

I would prefer all implementations (unix, windows, etc.) to have the same implementation. Please revert the changes to ALT. There might be good use for the ALT modifier, but that would be for another PR.

[paulie4]

That brings up a good question, why don't we add (r"\M-\<left>", "backward-word") and (r"\M-\<right>", "forward-word") to the default_keymap, so that way all implementations will have something useful for Alt+←?

Also, I just tested that, and it made me realize that the Lib\_pyrepl\windows_console.py code also needs to # queue the key, return the meta command in the special key == "\x00" section (see 46b22d1 for the fix and removal of treating Alt+← as Ctrl+←).

[eendebakpt]

Suggested change

	if key in ("left", "right") and key_event.dwControlKeyState & CTRL_ACTIVE:
	if key_event.dwControlKeyState & CTRL_ACTIVE:

I tried this locally and it works. For example for arrow up the ctrl up is passed on as the key. Currently it is ignored, but maybe it is better to just pass whatever we get and let some platform independent part of the code decide what to do with it?

[eendebakpt]

I don't know the answer. But why pass the ctrl modifier as a key f'ctrl {key}`, and the alt modifier using a special event?