title: Way to plot a second scaled y axis without explicitly using axes in matplotlib
body: <p>Here is currently how I am plotting using matplotlib. What I would like to include is a second axis that is labelled and is simply the reciprocal of y. I did see previous answers that used the formation of two axes - but is there a simple way of doing it using the more simplistic plt approach below?   </p>
  
  <pre><code> plt.scatter(chart_dict[chart][0], chart_dict[chart][1], c=colours[count], alpha=1.0, label=chart, lw = 0)
   plt.ylabel(y_lbl)
   plt.xlabel(x_lbl)
   plt.yscale('log')
  </code></pre>
  
  <p>To summarise, I simply want to plot the data, but have two y axes for the very same data. If I plot: {x=1, y=10}, we only have one point. But if we look to the yaxis, I can see of the left the y corresponds to 10, but on the right, it corresponds to 1/10=1.0.</p>