python gevent: unexpected output in KeyboardInterrupt

Running this code

import gevent

def f():
    while True:
        gevent.sleep(1)

if __name__ == '__main__':
    tasks = (gevent.spawn(f),)
    try:
        gevent.wait(tasks)
    except KeyboardInterrupt:
        print("KeyboardInterrupt trapped")

and then pressing a Ctrl-C, give me this output:

$ python receiver.py 
^CKeyboardInterrupt
Tue Aug  8 00:56:04 2017
KeyboardInterrupt trapped

Why?
It seems someone is writing the exit time on output.
How can I prevent that KeyboardInterrupt in the first line and the date in the second?