title: Create values from matplotlib subplot
body: <p>I have a matplotlib Figure object which I pass data into that I have created through another process.</p>
  <pre><code>data_figure = Figure()
  data_plot = data_figure.add_subplot(111)
  line = data_plot.plot(x_data, y_data)
  </code></pre>
  <p>Example graph</p>
  <p><img src="https://i.stack.imgur.com/GDHhc.png" alt="enter image description here" /></p>
  <p>Is there an appropriate way to get data values from the line which I haven't passed in? For example, if I passed in data for x=5 and x=15, could I find the y value for x=10 that the line has drawn?</p>