Is there a way to detach matplotlib plots so that the computation can continue?

Question

Dear all,

After these instructions in the Python interpreter one gets a window with a plot

from matplotlib.pyplot import *
plot([1,2,3])
show()
# other code

Unfortunately, I don't know how to continue to interactively explore the figure created by show() while the program does further calculations.

Is it possible at all? Sometimes calculations are long and it would help if they would proceed during examination of intermediate results.

Any help appreciated,

meteore.

Answer 1

It is better to always check with the library you are using if it supports usage in a non-blocking way.

But if you want a more generic solution, or if there is no other way, you can run anything that blocks in a separated process by using the multprocessing module included in python. Computation will continue:

from multiprocessing import Process
from matplotlib import plot, show

def plot_graph(*args):
    for data in args:
        plot(data)
    show()

p = Process(target=plot_graph, args=([1, 2, 3],))
p.start()

print 'yay'
print 'computation continues...'
print 'that rocks.'

print 'Now lets wait for the graph be closed to continue...:'
p.join()

That has the overhead of launching a new process, and is sometimes harder to debug on complex scenarios, so I'd prefer the other solution (using matplotlib's nonblocking API calls)

Answer 2

Use matplotlib's calls that won't block:

Using draw():

from matplotlib import plot, draw, show
plot([1,2,3])
draw()
print 'continue computation'

# at the end call show to ensure window won't close.
show()

Using interactive mode:

from matplotlib import plot, ion, show
ion() # enables interactive mode
plot([1,2,3]) # result shows immediatelly (implicit draw())

print 'continue computation'

# at the end call show to ensure window won't close.
show()

Answer 3

You may want to read this document in matplotlib's documentation, titled:

Using matplotlib in a python shell

Answer 4

In my case, I wanted to have several windows pop up as they are being computed. For reference, this is the way:

from matplotlib.pyplot import draw, figure, show
f1, f2 = figure(), figure()
af1 = f1.add_subplot(111)
af2 = f2.add_subplot(111)
af1.plot([1,2,3])
af2.plot([6,5,4])
draw() 
print 'continuing computation'
show()

PS. A quite useful guide to matplotlib's OO interface.