Python matplotlib: memory not being released when specifying figure size

Question

I\'m using matplotlib to generate many plots of the results of a numerical simulation. The plots are used as frames in a video, and so I\'m generating many of them by repeatedly

Answer 1

From the docstring for pylab.figure:

In [313]: pylab.figure?

If you are creating many figures, make sure you explicitly call "close" on the figures you are not using, because this will enable pylab to properly clean up the memory.

So perhaps try:

pylab.close()     # closes the current figure

Answer 2

Closing a figure is definitely an option, however, repeated many times, this is time consuming. What I suggest is to have a single persistent figure object (via static function variable, or as additional function argument). If that object is fig, the function will then call fig.clf() before each plotting cycle.

from matplotlib import pylab as pl
import numpy as np

TIMES = 10
x = np.linspace(-10, 10, 100)
y = np.sin(x)
def withClose():
    def plotStuff(i):
        fig = pl.figure()
        pl.plot(x, y + x * i, '-k')
        pl.savefig('withClose_%03d.png'%i)
        pl.close(fig)
    for i in range(TIMES):
        plotStuff(i)


def withCLF():
    def plotStuff(i):
        if plotStuff.fig is None:
            plotStuff.fig = pl.figure()
        pl.clf()
        pl.plot(x, y + x * i, '-')
        pl.savefig('withCLF_%03d.png'%i)
    plotStuff.fig = None

    for i in range(TIMES):
        plotStuff(i)

Here is the timing values

In [7]: %timeit withClose()
1 loops, best of 3: 3.05 s per loop

In [8]: %timeit withCLF()
1 loops, best of 3: 2.24 s per loop