QWidget: Must construct a QApplication before a QPaintDevice

HI, I am new to GNUradio. I have run into a problem when i tried to run
a gnuradio python file but
the GUI didn’t start. Below is the output.

Executing: /usr/bin/python2 -u
/home/champly/gr-ieee802-11/examples/wifi_loopback.py

linux; GNU C++ version 5.4.0 20160609; Boost_105800;
UHD_003.010.000.git-249-gef57ffcb

QWidget: Must construct a QApplication before a QPaintDevice

Done


System Info:

champly@champly:~/gr-ieee802-11/examples$ lsb_release -s -d
Ubuntu 16.04 LTS

hamply@champly:~/gr-ieee802-11/examples$ uname -a
Linux champly 4.4.0-31-generic #50-Ubuntu SMP Wed Jul 13 00:07:12 UTC
2016 x86_64 x86_64 x86_64 GNU/Linux

Thank you,
Best regard