title: store python plot as a variable and reload it to overlay another plot
body: <p>In Mathematica you can store plots in variables and then overlay them at some later time. For example,</p>
  
  <pre><code>plt1 = Plot[Cos[x],{x,0,Pi}];
  plt2 = Plot[Sin[x],{x,0,Pi}];
  plt3 = Plot[x,{x,0,Pi}];
  
  Show[plt1,plt2]
  Show[plt1,plt3]
  </code></pre>
  
  <p>gives two plots, one overlays cos(x) and sin(x) plots, and the other overlays cos(x) and x plots. Therefore, I do not need to replot cos(x) for the second overlay since it is already saved in plt1. </p>
  
  <p>I am wondering the same thing can happen in python too. I have a 2D function that is time-consuming to plot, and I need to replot it and overlay it with some other data every time. Can I plot it only once and then overlay it in with plots of other data? </p>