Add 'Open Input in Editor' support to PyREPL

[tanloong]

Feature or enhancement

Although multiline editing has been significantly improved in the new REPL, for users who are comfortable with Vim or other editors, writing long or complex code blocks in it can still be a little bit inconvenient. Editing the current input in an external editor can unlock the power of users' editor.

This is a common feature in many other shells:

• IPython: open_input_in_editor
• Bash: edit-and-execute-command (C-x C-e)
• Fish: M-e
• PostgreSQL psql: \e command
• PowerShell: ViEditVisually

Proposed behavior:

1. Default shortcut: C-x C-e
2. Create a temporary file with .py suffix and write reader.buffer to it
3. Open it in a subprocess with $VISUAL or $EDITOR. Fall back to vi (Unix-like) or notepad (Windows) if neither variable is set
4. After saving and exiting, load the content to reader.buffer and delete the temporary file.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

https://discuss.python.org/t/add-edit-in-external-editor-to-pyrepl-ctrl-x-ctrl-e/107170

Linked PRs

• gh-149392: Add "Open Input in Editor" support in PyREPL #149393