Call to signal.signal( ) in application.py fails due to signal.getsignal( ) returning None.

Hi,

I've been integrating ipython into an application for a number of years, but recently found a failure which is coming from prompt-toolkit. The issue on only in v3 of the code. The problem occurs at
prompt-toolkit/python-prompt-toolkit/application.py:727 (in the master)

signal.signal(signal.SIGWINCH, previous_winch_handler)

previous_winch_handler was assigned at line 691.

previous_winch_handler = signal.getsignal(signal.SIGWINCH)

This call returned None, and then the call on line 727 fails, since None is not an acceptable value for signal.signal().

Just prior to invoking the Python interpreter in my C++ application, I use signal( SIGWINCH, SIG_DFL ) to remove any installed signal handler from the C++ code. I also tried SIG_IGN, but to no avail, getsignal() still returns None. One workaround was to execute the following in my Python code before initializing IPython, and subsequently calling prompt-toolkit.

signal.signal( signal.SIGWINCH, signal.SIG_DFL ) 

So my question is; should the prompt-toolkit code account for the fact that getsignal() could return None? Or is there something better that I should do in my application? Or is my current workaround the way forward?

Regards,
John

Start in python-prompt-toolkit/application.py around lines 691 and 727, tracing how SIGWINCH handlers are saved and restored. Reproduce the embedded-application case described here, then verify that the chosen handling accepts the reported getsignal() result without breaking normal signal restoration.