title: How to extract points from a graph?
body: <p>I have a question.</p>
  
  <p>I have plotted a graph using Matplotlib like this:</p>
  
  <pre><code>from matplotlib import pyplot
  import numpy
  from scipy.interpolate import spline
  
  widths = numpy.array([0, 30, 60, 90, 120, 150, 180])
  heights = numpy.array([26, 38.5, 59.5, 82.5, 120.5, 182.5, 319.5])
  
  xnew = numpy.linspace(widths.min(),widths.max(),300)
  heights_smooth = spline(widths,heights,xnew)
  
  pyplot.plot(xnew,heights_smooth)
  pyplot.show()
  </code></pre>
  
  <p>Now I want to query a height value using width value as an argument. I cannot seem to find how to do that. Please help! Thanks in advance!</p>