Re: [Matplotlib-users] real time plotting

[David H. <dh...@gm...>]

Someone may have to correct me, but I think this has to do with the Qt4 
event loop and it not being run properly. When you get into real time 
plotting it can get kind of tricky. In your case (I got the same 
results). I have made real-time PyQt4 GUIs before and have always used 
separate QThreads and Qt signals/slots to update the plot. I've never 
used GTK so I'm not sure why that worked vs Qt, I would think they would 
use similar principles but matplotlib does some magic behind the scenes 
sometimes. You can see different results if you comment out the while 
loop and import the module into your python/ipython interpreter. After 
doing this you'll see the figure pop up (you don't even need the 
fig.canvas.show() for this part if interactive mode is on. I went one 
step further and turned the while loop into a function:

def one_iter(i):
     # Contents of while loop

Calling this in the interpreter shows the figure updating after each 
call, but running in a loop (even with sleep) won't show any updates 
until the loop is done. In my opinion you have a few choices that really 
depend on your programming comfort level:

1. Don't make a real-time plot.
         Do you really need a real-time plot that updates from some 
external source?
2. Maybe you should look at the matplotlib animation functionality 
(http://matplotlib.org/api/animation_api.html). I like this tutorial: 
http://jakevdp.github.com/blog/2012/08/18/matplotlib-animation-tutorial/. This 
won't get you a real-time GUI exactly, but it can help if what you're 
doing isn't too complicated. It can also be nice for making videos of 
plot animations.
3. If you need a GUI with multiple plots and you need for future feature 
creep, I would research making PyQt4 GUIs, QThreads, Qt signals and 
slots, and putting matplotlib figures into a PyQt4 GUI. This is complex 
if you are not familiar with GUI programming and will take a while.

Sorry I couldn't be of more help, but it really depends on what exactly 
you are doing.  Mainly, what do you mean by real-time? Do you really 
mean animation? Let me know what you come up with, I'm interested.

-Dave

P.S. Why use a while loop? You can do the same thing with:

     for i in range(1000):
         # Do stuff

On 3/11/13 10:34 AM, Neal Becker wrote:
> I added fig.canvas.show(). It still does nothing.
>
> If I add
> mpl.use ('GTK'), now it seems to be doing realtime plotting.
>
> import matplotlib as mpl
>
> import matplotlib.pyplot as plt
> plt.ion()
> import numpy as np
> fig=plt.figure()
> plt.axis([0,1000,0,1])
>
> i=0
> x=list()
> y=list()
>
> fig.canvas.show()
> while i <1000:
>     temp_y=np.random.random()
>     x.append(i)
>     y.append(temp_y)
>     plt.scatter(i,temp_y)
>     i+=1
>     plt.draw()
>
>
>
> On Mon, Mar 11, 2013 at 10:35 AM, David Hoese <dh...@gm... 
> <mailto:dh...@gm...>> wrote:
>
>     Oops forgot to change the subject line.
>
>     On 3/11/13 9:34 AM, David Hoese wrote:
>
>         You likely need to "show()" the canvas. I usually do this by
>         calling "fig.canvas.show()" before the for loop.
>         Since you are using a Qt4 backend the canvas used by the
>         figure is a QWidget, the basic component of a Qt4 GUI. I don't
>         know if there is a more matplotlib specific way of doing this,
>         but when dealing with a larger system this is how I do it.
>
>         I would also add a sleep ("from time import sleep") of a
>         couple seconds for testing to make sure you are getting
>         through the entire for loop before you can see it.
>
>         Please CC in any replies, thanks.
>
>         -Dave
>
>
>         On 3/11/13 8:58 AM, ndb...@gm...
>         <mailto:ndb...@gm...> wrote:
>
>             I want to update a plot in real time.  I did some goog
>             search, and saw various
>             answers.  Trouble is, they aren't working.
>
>             Here's a typical example:
>
>             import matplotlib.pyplot as plt
>             import numpy as np
>             fig=plt.figure()
>             plt.axis([0,1000,0,1])
>
>             i=0
>             x=list()
>             y=list()
>
>             while i <1000:
>                  temp_y=np.random.random()
>                  x.append(i)
>                  y.append(temp_y)
>                  plt.scatter(i,temp_y)
>                  i+=1
>                  plt.draw()
>
>             If I run this, it draws nothing.
>
>             This is my matplotlibrc:
>             backend : Qt4Agg
>             mathtext.fontset: stix
>
>
>
>