# Matplotlib runtime error **URL:** \ **Category:** GNU Radio\ **Created:** [May 2, 2014, 2:19pm UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839 "2014-05-02T14:19:16Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [May 2, 2014, 2:19pm UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839/1 "2014-05-02T14:19:16Z")
Gurus, I try to transfer an image file via a pair of USRPs. At the receiver side, the data is fed into a custom block, where it plots the image in realtime using matplotlib’s pyplot.imshow(). Unfortunately, in the work() function, the pyplot.draw() causes below runtime error. handler caught exception: main thread is not in main loop Traceback (most recent call last): File “/usr/local/lib/python2.7/dist-packages/gnuradio/gr/gateway.py”, line 55, in eval try: self.\_callback() File “/usr/local/lib/python2.7/dist-packages/gnuradio/gr/gateway.py”, line 160, in \_\_gr\_block\_handle ) for i in self.\_\_out\_indexes], File “/usr/local/lib/python2.7/dist-packages/activecat/image\_sink1.py”, line 72, in work self.axes1.figure.canvas.draw() #pyplot.draw() File “/usr/lib/pymodules/python2.7/matplotlib/backends/backend\_tkagg.py”, line 349, in draw tkagg.blit(self.\_tkphoto, self.renderer.\_renderer, colormode=2) File “/usr/lib/pymodules/python2.7/matplotlib/backends/tkagg.py”, line 13, in blit tk.call(“PyAggImagePhoto”, photoimage, id(aggimage), colormode, id(bbox\_array)) RuntimeError: main thread is not in main loop thread[thread-per-block[1]: \]: caught unrecognized exception The custom block (perform plotting) is written in Python, as below: #!/usr/bin/env python # -_- coding: utf-8 -_- import numpy from gnuradio import gr from matplotlib import image, pyplot class image\_sink1(gr.sync\_block): ``` def __init__ (self): gr.sync_block. __init__ ( self, name="image_sink1", in_sig=[numpy.complex64], out_sig=None) pyplot.figure() pyplot.ion() pyplot.show() self.axes1 = pyplot.gca() #self.win = self.axes1.figure.canvas.manager.window #self.win.after(100,animate) self.completed = False self.img2 = numpy.zeros( (150,150,4), numpy.uint8 ) self.coordinate = self.coordinate_stream() def coordinate_stream(self): for y in range(150): for x in range( 0, 150, 2 ): yield y,x def work(self, input_items, output_items): in0 = input_items[0] if self.completed: return -1 for sample1 in in0: try: y,x = next( self.coordinate ) if sample1.real > 0: self.img2[y,x] = numpy.array([255,255,255,255]) else: self.img2[y,x] = numpy.array([0,0,0,255]) if sample1.imag > 0: self.img2[y,x+1] = numpy.array([255,255,255,255]) else: self.img2[y,x+1] = numpy.array([0,0,0,255]) except StopIteration: print "Receiver side completed!" self.complete = True self.axes1.imshow( self.img2 ) self.axes1.figure.canvas.draw() # or, pyplot.draw(), both ``` gives error !!! ``` return in0.size ``` Please advise, thanks in advance. ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [May 2, 2014, 2:58pm UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839/2 "2014-05-02T14:58:36Z")
On Fri, May 2, 2014 at 8:49 AM, Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: > out of your flow graph into your GUI. > > Greetings, > Marcus Tim’s written a number of blocks like this: > **[GitHub - osh/gr-pyqt: pyqt based plotters intended for plotting bursted...](https://github.com/osh/gr-pyqt)** > > pyqt based plotters intended for plotting bursted events in gnu radio Tom ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [May 2, 2014, 2:53pm UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839/3 "2014-05-02T14:53:41Z")
Hi Activecat, typical GUI problem; background is that X applications are inherently hard to multithread, which basically requires graphical toolkits to run in a main loop. This conflicts with every block being run in its own thread. The easiest solution nowadays should be that you generate a QT flow graph in GRC, use PyQT to generate your GUI, register a message handler and integrate matplotlib (there are examples out there, just don’t have one at my fingertips right now), and use the message passing interface to get data out of your flow graph into your GUI. Greetings, Marcus ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [May 8, 2014, 9:32am UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839/4 "2014-05-08T09:32:02Z")
On Fri, May 2, 2014 at 8:56 PM, Tom R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > integrate matplotlib (there are examples out there, just don’t have one at > > Tom I am now learning Qt in order to use it with gnuradio. Q1: In gnuradio we use Qt Widgets, but not Qt Quick at all. Is this correct? Q2: In roadmap when will gnuradio start to use Qt5, gnuradio v3.8 ..? ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [May 18, 2014, 2:27pm UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839/5 "2014-05-18T14:27:02Z")
* * * Discuss-gnuradio mailing list removed\_email\_address@domain.invalid [https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [May 8, 2014, 3:31pm UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839/6 "2014-05-08T15:31:19Z")
On Thu, May 8, 2014 at 3:30 AM, Activecat [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > > > > Tim’s written a number of blocks like this: > > > > [GitHub - osh/gr-pyqt: pyqt based plotters intended for plotting bursted events in gnu radio · GitHub](https://github.com/osh/gr-pyqt) > > > > Tom > > I am now learning Qt in order to use it with gnuradio. > Q1: In gnuradio we use Qt Widgets, but not Qt Quick at all. Is this > correct? Correct. > Q2: In roadmap when will gnuradio start to use Qt5, gnuradio v3.8 ..? Uncertain. I haven’t spent enough time, yet, with QT5 to know for sure and determine what we get (features) and what we lose (older distro support). More likely, this will be a 3.9 thing. Tom ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [May 18, 2014, 6:54pm UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839/7 "2014-05-18T18:54:05Z")
On Sun, May 18, 2014 at 9:00 AM, Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: > As I explained, you’ll have a hard time getting GUI to run in a block, > Marcus I agree with Marcus. Don’t try and use/abuse matplotlib for this purpose. I pointed to Tim’s repo of PyQT/QWT blocks to show you how to use those tools to build GUIs in Python blocks. Tom ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [May 19, 2014, 5:08am UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839/8 "2014-05-19T05:08:53Z")
On Mon, May 19, 2014 at 12:52 AM, Tom R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > about your approach. > > > > Greetings, > > Marcus > > I agree with Marcus. Don’t try and use/abuse matplotlib for this purpose. > I pointed to Tim’s repo of PyQT/QWT blocks to show you how to use those > tools to build GUIs in Python blocks. > > Tom Thank you very much. ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [May 18, 2014, 3:01pm UTC](https://www.ruby-forum.com/t/matplotlib-runtime-error/240839/9 "2014-05-18T15:01:30Z")
Hi, I think real-time and matplotlib kind of contradict in the first place - really, matplotlib’s performance is terrible. As a rule, it’s Assisi generally a bad idea to let your data file update your GUI. Usually, you want something like a check every tenth of a second, if data has arrived, and then updating your GUI accordingly. Otherwise, you will either end up with refresh rates that are unnecessarily high (e.g. 200fps) or a GUI not reacting to events (e.g. resizing) by redrawing. So that’s two things bad about your approach. As I explained, you’ll have a hard time getting GUI to run in a block, since by principle, GR blocks can not run in the main thread, and things like Tim’s qwt plot go through death, wind, fire and message passing to get data out of the blocks’ threads and into the GUI thread. Anyway, with matplotlib and pyqt to wrap the canvas in a qt application and a little googling you can hack together guis that should work with the qt generate option - no guarantee though. I’d rather get used to qwt in most cases than stick with matplotlib… Greetings, Marcus