Hello everybody,
I'm building a small Tkinter GUI using matplotlib, in which I have to
change/update plots quite often depending on user input (with different
contents & sizes, in different places in the GUI, etc.; but always only
one figure at a time).
As a first resort, I regenerated the figures with plt.figure(...) whenever
necessary; unfortunately, the program happily accumulated memory with
every new figure until the computer would no longer cooperate in a timely
fashion. The following minimal script should demonstrate the tendency:
--- start of script ---
import math
from Tkinter import Tk, Button
import Tkconstants
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
from matplotlib.figure import Figure
from matplotlib import pyplot as plt
def replot():
global globalCanvas, globalFigure, plotShift
# any variety of clean-up calls
if globalFigure is not None:
plt.close()
globalCanvas.get_tk_widget().destroy()
globalFigure.clf()
globalFigure = Figure(dpi=120, figsize=(4, 4))
globalCanvas = FigureCanvasTkAgg(globalFigure, master=root)
globalCanvas.get_tk_widget().grid(row=0, column=1)
xVals = xrange(100)
ax = globalFigure.add_subplot(111)
ax.plot(xVals, [math.sin(x + plotShift) for x in xVals])
plotShift += 10
# MAIN
globalCanvas = None
globalFigure = None
plotShift = 0 # just to see the plot change
root = Tk()
draw_button = Button(root, text="Replot", command=replot)
draw_button.grid(row=0, column=0, sticky=Tkconstants.N)
root.mainloop()
--- end of script ---
I have tried various clean-up calls, but the effect (of memory piling up)
is always the same. Using objgraph (http://mg.pov.lt/objgraph/), I took a
look at object counts by adding the following snippet at the end of the
"replot" call:
--- start of insertion ---
import gc
import objgraph
gc.collect()
print "---"
for c in ('FigureCanvasTkAgg', 'Figure'):
print "{}\t{}".format(len(objgraph.by_type(c)), c)
--- end of insertion ---
The output shows that the total number of both Figures and
FigureCanvasTkAggs increases constantly (i.e., one each after the first
call, then two each, etc.), whereas I had expected that old ones get
released, and that the count remains at one each.
Now I am wondering if I am missing some detail, e.g., some other clean-up
procedure? Or should this work & could be a memory leak in matplotlib or
Tkinter? And/or is this approach (of generating a new figure every time)
not recommended in the first place? I tried reusing the figure, but some
aspects like changing the layout in the GUI and applying new size and dpi
then proved tricky in their own ways.
Many thanks in advance,
Hans
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