TypeError: signal handler must be signal.SIG_IGN, signal.SIG_DFL, or a callable object

[sametmax]

If you register a signal handler for SIGTERM, start the event loop then kill it with CTRL + C, you get this error:

Exception ignored in: <bound method BaseEventLoop.__del__ of <_UnixSelectorEventLoop running=False closed=True debug=False>>
Traceback (most recent call last):
  File "/usr/lib/python3.5/asyncio/base_events.py", line 431, in __del__
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 58, in close
  File "/usr/lib/python3.5/asyncio/unix_events.py", line 140, in remove_signal_handler
  File "/usr/lib/python3.5/signal.py", line 47, in signal
TypeError: signal handler must be signal.SIG_IGN, signal.SIG_DFL, or a callable object

Minimal code to get the error:

import signal
import asyncio

loop = asyncio.get_event_loop()

def bar():
    loop.stop()

loop.add_signal_handler(signal.SIGTERM, bar)
loop.run_forever()

This will not occur if you register a handler for another signal, such as SIGINT.

[vxgmichel]

This will not occur if you register a handler for another signal, such as SIGINT.

It does actually occur for all signals except SIGINT (SIGINT has a special treatment in loop.remove_signal_handler). This error has been reported on bugs.python.org as issue32548. I've looked into it, and it turns out this problem is unrelated to asyncio. It can be reproduced using the _signal module only:

import _signal

class A:
    def __del__(self):
        _signal.signal(_signal.SIGTERM, _signal.SIG_DFL)

a = A()

It also affects python 2. This happens because the signalmodule resources are cleared before the garbage collector calls a.__del__. It causes this if statement to fail and a misleading TypeError is raised.

It's quite similar to issue 14173 (fixed in 2012).

[sametmax]

Thanks. Let me close this then, no need for duplicate tickets.