Error when plotting with matplotlib.pyplot.plot()

Question

The following code gives errors I don't understand why :

    import numpy as np
    import matplotlib.pyplot as plt
    a = np.arange(10)
    plt.plot(a)
    [<matplotlib.lines.Line2D at 0x116be8890>]
    plt.show()

    2013-01-29 10:58:18.891 Python[27257:903] *** __NSAutoreleaseNoPool(): Object 0x105b27810 of class NSCFArray autoreleased with no pool in place - just leaking
    2013-01-29 10:58:18.893 Python[27257:903] *** __NSAutoreleaseNoPool(): Object 0x105b37f60 of class __NSFastEnumerationEnumerator autoreleased with no pool in place - just leaking
    2013-01-29 10:58:18.895 Python[27257:903] *** __NSAutoreleaseNoPool(): Object 0x105bee900 of class NSObject autoreleased with no pool in place - just leaking

I have matplotlib 1.2.0, numpy 1.6.2, python 2.7.3 and ipython 0.13.1. The packages have been installed with macports. This is doing it on Mac OS 10.6.8, and I don't see it on 10.7.5.

Edit : this post shows the same error, although no solution has been clearly found

Answer 1

I haven't found a solution yet. My workaround has been to install another backend : qt4. This requires to do :

    sudo port install qt4-mac
    sudo port install py27-qt4

and then modify (or create if None) the file ~/.matplotlib/matplotlibrc by adding :

    backend : QT4Agg

Then the above text works without problem.

Answer 2

I am also having this problem, my work around is to add:

plt.ion()

before the first plot command. This turns on the interactive plotting mode and it makes the errors go away.