`interrupt-process` doesn't work for Python on Windows

`interrupt-process` doesn't work for Python on Windows

[Joost]

Hi,

After running into an issue with a package that enhances Emacs' inferior Python shell and a long back and forth with the package's maintainer, the maintainer feels there might be a bug in Emacs. Specifically, the command `interrupt-process` is not able to interrupt the Python process on Windows. Details are in this message and in the message's thread:

https://github.com/jdtsmith/python-mls/issues/8#issuecomment-1033120469

To quote the relevant section:

====================
Here is the issue: `interrupt-process` (and internal C function) does not function correctly to interrupt Python on Windows emacs! While at the command prompt, a simple `C-c` does correctly interrupt (and returns `Keyboard Interrupt\n>>> ` promptly), `interrupt-process` does not, and leads to the double-traceback you reported earlier, but _only after you send another newline_. This is incorrect behavior, and seems to represent a bug in the way Emacs sends interrupts on Windows, which differs from `C-c` in the command prompt.

It's easy to verify the difference:

* `C-c` at `>>> ` python prompt in "Command Prompt": immediate `KeyboardInterrupt` and prompt.
* `C-c C-c` at `>>> ` python prompt in Emacs _Python_: no `KeyboardInterrupt`.

====================

Should I file a bug report about this? Or is this something Emacs can do nothing about?

TIA

Joost


-- 
Joost Kremers
Life has its moments

Re: `interrupt-process` doesn't work for Python on Windows

[Eli Zaretskii]

> Date: Wed, 09 Feb 2022 10:17:33 +0100
> From: Joost <joostkremers@fastmail.fm>
> 
> https://github.com/jdtsmith/python-mls/issues/8#issuecomment-1033120469
> 
> To quote the relevant section:
> 
> ====================
> Here is the issue: `interrupt-process` (and internal C function) does not function correctly to interrupt Python on Windows emacs! While at the command prompt, a simple `C-c` does correctly interrupt (and returns `Keyboard Interrupt\n>>> ` promptly), `interrupt-process` does not, and leads to the double-traceback you reported earlier, but _only after you send another newline_. This is incorrect behavior, and seems to represent a bug in the way Emacs sends interrupts on Windows, which differs from `C-c` in the command prompt.
> 
> It's easy to verify the difference:
> 
> * `C-c` at `>>> ` python prompt in "Command Prompt": immediate `KeyboardInterrupt` and prompt.
> * `C-c C-c` at `>>> ` python prompt in Emacs _Python_: no `KeyboardInterrupt`.
> 
> ====================
> 
> Should I file a bug report about this? Or is this something Emacs can do nothing about?

As I responded there, Emacs on MS-Windows emulates SIGINT to a
sub-process by injecting an actual Ctrl-C character into the
sub-process's input stream.  But that might not do what you expect,
because Emacs on Windows communicates with sub-processes via pipes,
not via (pseudo)console devices, and thus Python could react to Ctrl-C
differently than it reacts when run from the console.

So at least at the moment, this doesn't look like an Emacs problem.