title: warning about too many open figures
body: <p>In a script where I create many figures with <code>fix, ax = plt.subplots(...)</code>, I get the warning <em>RuntimeWarning: More than 20 figures have been opened. Figures created through the pyplot interface (<code>matplotlib.pyplot.figure</code>) are retained until explicitly closed and may consume too much memory.</em> </p>
  
  <p>However, I don't understand <em>why</em> I get this warning, because after saving the figure with <code>fig.savefig(...)</code>, I delete it with <code>fig.clear(); del fig</code>. At no point in my code, I have more than one figure open at a time. Still, I get the warning about too many open figures.  What does that mean / how can I avoid getting the warning?</p>