[Python] Reset Python SIGINT to default signal handler

Version info:

• OS: Windows 7
• Python version 3.3.5

Below is small piece of test code I was playing around with. The aim was to ignore CTRL-C being pressed while certain code was being executed, after which the CTRL-C behaviour would be restored.

import signal
import time

try:
# marker 1
print('No signal handler modifications yet')
print('Sleeping...')
time.sleep(10)

# marker 2
signal.signal(signal.SIGINT, signal.SIG_IGN)
print('Now ignoring CTRL-C')
print('Sleeping...')
time.sleep(10)

# marker 3
print('Returning control to default signal handler')
signal.signal(signal.SIGINT, signal.SIG_DFL)
print('Sleeping...')
time.sleep(10)

except KeyboardInterrupt:
print('Ha, you pressed CTRL-C!')


What I've observed while playing around with this:

• CTRL-C sent between marker 1 and marker 2 will be processed by the exception handler (as expected).
• CTRL-C sent between marker 2 and marker 3 is ignored (still, as expected)
• CTRL-C sent after marker 3 is processed but will not jump to the exception handler. Instead, Python just terminates immediately.

Also, consider this:

>>>import signal

>>>signal.getsignal(signal.SIGINT)
<built-in function default_int_handler>

>>> signal.getsignal(signal.SIGINT) is signal.SIG_DFL
False

>>> signal.signal(signal.SIGINT, signal.SIG_DFL)
<built-in function default_int_handler>

>>> signal.getsignal(signal.SIGINT) is signal.SIG_DFL
True


So initially, while the signal handler is considered the default signal handler, it seems to be a different handler than the one defined by SIG_DFL.

If anyone could shed some light on this, especially while the exception handler is ignored after restoring the signal handler to SIG_DFL.

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