title: Python and plot() : how to limit the number of x-axis ticks (labels)
body: <p>I have two lists, same size, one is y_data and one is x_data
  x_data is a time hh:mm:ss during day, in fact each minute
  each serie is 1440 long.</p>
  
  <p>problem is :</p>
  
  <pre><code>fig = Figure(figsize=(4,3))
  a = gif.add_subplot(111)
  a.plot(x_data, y_data)
  </code></pre>
  
  <p>give an unreadable x_axis (too many labels), if i reduce x_data to <code>[range(24)]</code> for instance, plot gives an error.</p>
  
  <p>Question :</p>
  
  <p>I'd like to have only 24 items on x_axis scale (each hour, so 1 item each 60 x_data points)
  is there a simple way to achieve this ? <code>set_autoscale_on(False)</code> and then manually setting limits seems a very complex way to achieve this (and I would loose the benefits from autoscaling on y axis).
  Another solution seems to involve <code>a.xaxis.set_ticks()</code> but i have to crate a new serie.</p>
  
  <p>o I'd like to use x_data but just limit the number of ticks shown on x_axis, is there a way to do it ?</p>