asyncio REPL swallows KeyboardInterrupt while editing

[iomintz]

BPO	38958
Nosy	@asvetlov, @1st1, @iomintz

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-12-03.00:10:02.040>
labels = ['3.8', '3.9', 'expert-asyncio']
title = 'asyncio REPL swallows KeyboardInterrupt while editing'
updated_at = <Date 2019-12-03.00:10:02.040>
user = 'https://github.com/iomintz'

bugs.python.org fields:

activity = <Date 2019-12-03.00:10:02.040>
actor = 'iomintz'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2019-12-03.00:10:02.040>
creator = 'iomintz'
dependencies = []
files = []
hgrepos = []
issue_num = 38958
keywords = []
message_count = 1.0
messages = ['357738']
nosy_count = 3.0
nosy_names = ['asvetlov', 'yselivanov', 'iomintz']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue38958'
versions = ['Python 3.8', 'Python 3.9']

[iomintz]

"python3 -m asyncio" swallows KeyboardInterrupt while editing a line.

Problem steps:
==============

• run python -m asyncio
• press ^C

Expected behavior (normal CPython REPL, as well as python -m code):
==================================================================

The current input line is abandoned and "\nKeyboardInterrupt" is printed.

Sample for "spam^C" with the normal REPL:
-----------------------------------------

Python 3.8.0 (default, Oct 23 2019, 18:51:26) 
[GCC 9.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> spam
KeyboardInterrupt

Python 3.9.0a1+ (heads/master:a62ad4730c, Dec  2 2019, 17:38:37) 
[GCC 9.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> spam
KeyboardInterrupt

Sample for "spam^C" in the InteractiveConsole REPL, as invoked by python -m code:
-----------------------------------------------------------------------------------

Python 3.8.0 (default, Oct 23 2019, 18:51:26) 
[GCC 9.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> spam
KeyboardInterrupt

Python 3.9.0a1+ (heads/master:a62ad4730c, Dec  2 2019, 17:38:37) 
[GCC 9.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> spam
KeyboardInterrupt

Actual behavior:
================

The KeyboardInterrupt is ignored, the current input line remains on screen, and a new line is not started:

asyncio REPL 3.8.0 (default, Oct 23 2019, 18:51:26) 
[GCC 9.2.0] on linux
Use "await" directly instead of "asyncio.run()".
Type "help", "copyright", "credits" or "license" for more information.
>>> import asyncio
>>> spam

asyncio REPL 3.9.0a1+ (heads/master:a62ad4730c, Dec  2 2019, 17:38:37) 
[GCC 9.2.0] on linux
Use "await" directly instead of "asyncio.run()".
Type "help", "copyright", "credits" or "license" for more information.
>>> import asyncio
>>> spam

Workaround
==========

If editing a continued block (ie a line prefixed by sys.ps2 / "..."), enter any invalid syntax (such as unindented code) to cancel the current block. If editing a single line, press ^U to clear the line.

OS Details
==========

Arch Linux, python extra/python 3.8.0-1.

[kumaraditya303]

IIUC the code is run in a separate thread and since only main thread can handle signals it doesn't work. It is a runtime limitation so there is no easy fix I can think of.

[arhadthedev]

Closing because Kumar gave an exhaustive technical explanation.