[issue39169] TypeError: 'int' object is not callable if the signal handler is SIG_IGN

[Antoine Pitrou]

Change by Antoine Pitrou :


--
resolution:  -> duplicate
stage: test needed -> resolved
status: open -> closed
superseder:  -> Possible race condition between signal catching and 
signal.signal

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[issue39169] TypeError: 'int' object is not callable if the signal handler is SIG_IGN

[Terry J. Reedy]

Change by Terry J. Reedy :


--
stage:  -> test needed
versions: +Python 3.9 -Python 3.6

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[issue39169] TypeError: 'int' object is not callable if the signal handler is SIG_IGN

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
nosy: +ethan.furman, serhiy.storchaka

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[issue39169] TypeError: 'int' object is not callable if the signal handler is SIG_IGN

[Ronald Li]

New submission from Ronald Li :

The attached script ign2ndsig.py demonstrates an attempted way to handle 
signals at most once and ignore any subsequent signals. SIGINT and SIGTERM are 
used in the demo.


In Python 3.5, the subprocess would go into one of the "except 
KeyboardInterrupt:" or "except SystemExit:" blocks before doing "finally:" and 
exiting zero:


# execute the script with no args:
# ./ign2ndsig.py

subproc: sys.version_info(major=3, minor=5, micro=9, releaselevel='final', 
serial=0)
raising KeyboardInterrupt
handling KeyboardInterrupt
doing finally
rc: 0



In Python 3.6, 3.7 or 3.8, the subprocess would go into neither the "except 
KeyboardInterrupt:" nor "except SystemExit:" blocks before doing "finally:" and 
exiting non-zero, with a traceback like this:


subproc: sys.version_info(major=3, minor=6, micro=10, releaselevel='final', 
serial=0)
raising KeyboardInterrupt
doing finally
Traceback (most recent call last):
  File "./ign2ndsig.py", line 30, in subproc
input()
  File "./ign2ndsig.py", line 18, in handler
raise KeyboardInterrupt
KeyboardInterrupt

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "./ign2ndsig.py", line 58, in 
subproc()
  File "./ign2ndsig.py", line 32, in subproc
printef('handling KeyboardInterrupt')
  File "./ign2ndsig.py", line 10, in printef
print(*objects, file=sys.stderr, flush=True)
TypeError: 'int' object is not callable
rc: 1



More on the behaviors of ign2ndsig.py :
1. Replacing SIG_IGN at line 14 and 15 with a no-op Python function "fixes" the 
problem - such that in Python 3.6, 3.7 or 3.8, it'd behave similarly to the 
Python 3.5 output above.
2. Sending a SIGTERM then a SIGINT (instead of a SIGINT followed by a SIGTERM) 
(i.e. reversing the order of SIGINT and SIGTERM) at line 49-50 results in a 
similar behavior (that the TypeError is raised).
3. Sending 2 SIGINTs or 2 SIGTERMs (instead of 1 SIGINT + 1 SIGTERM) (i.e. 
sending the same signal twice) at line 49-50 does NOT result in the TypeError.


Potentially related issues:

_thread.interrupt_main() errors if SIGINT handler in SIG_DFL, SIG_IGN
https://bugs.python.org/issue23395

Turn SIG_DFL and SIG_IGN into functions
https://bugs.python.org/issue23325

--
files: ign2ndsig.py
messages: 359071
nosy: Ronald Li
priority: normal
severity: normal
status: open
title: TypeError: 'int' object is not callable if the signal handler is SIG_IGN
type: behavior
versions: Python 3.6, Python 3.7, Python 3.8
Added file: https://bugs.python.org/file48810/ign2ndsig.py

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