New submission from Ryan Petrello:

I may have found a bug in SIGALRM handling in Python3.5.  I've not been able to 
reproduce the same issue in Python2.7 or 3.4.  Here's a simple example that 
illustrates the issue (which I'm able to reproduce on OS X 10.11.3 El Capitan 
and Ubuntu 14.04):

$ python2 --version; python3.4 --version; python3.5 --version
Python 2.7.11
Python 3.4.4
Python 3.5.1

$ cat
import signal, time

def handler(signum, frame):
    print('Signal handler called with signal %s' % signum)

# Set the signal handler and a 1-second alarm
signal.signal(signal.SIGALRM, handler)

# We should not actually sleep for 10 seconds

$ time python2
Signal handler called with signal 14
python2  0.04s user 0.02s system 5% cpu 1.075 total

$ time python3.4
Signal handler called with signal 14
python3.4  0.07s user 0.01s system 7% cpu 1.092 total

$ time python3.5
Signal handler called with signal 14
python3.5  0.09s user 0.02s system 1% cpu 10.115 total

Note that when run under python3.5, the program does not exit until 10 seconds 
have passed.

components: Library (Lib)
messages: 278835
nosy: ryan.petrello
priority: normal
severity: normal
status: open
title: SIGALRM fails to interrupt time.sleep() call on Python 3.6
versions: Python 3.5

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