title: Python: plt.plot(x,y) ValueError: Unrecognized character S in format string
body: <p>Quarter is seasonal data, such as '2009Q1','2010Q4'...
  Size is a float data, such as '12.1', '14.3' ...
  The data type is as below:</p>
  
  <pre><code>Quarter                            object
  Size                              float64
  </code></pre>
  
  <p>While I try to plot these two columns, there is an error:</p>
  
  <pre><code>plt.plot('Quarter','Size')   
  plt.show()
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>ValueError: Unrecognized character S in format string
  </code></pre>
  
  <p>Does it mean I need to transfer the season data to another format?
  I do not know how to change the type.
  Thanks!</p>