title: Show decimal places and scientific notation on the axis of a matplotlib plot
body: <p>I am plotting some big numbers with matplotlib in a pyqt program using python 2.7. I have a y-axis that ranges from 1e+18 to 3e+18 (usually).  I'd like to see each tick mark show values in scientific notation and with 2 decimal places. For example 2.35e+18 instead of just 2e+18 because values between 2e+18 and 3e+18 still read just 2e+18 for a few tickmarks.  Here is an example of that problem.</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  fig = plt.figure()
  ax = fig.add_subplot(111)
  x = np.linspace(0, 300, 20)
  y = np.linspace(0,300, 20)
  y = y*1e16
  ax.plot(x,y)  
  ax.get_xaxis().set_major_formatter(plt.LogFormatter(10,  labelOnlyBase=False))
  ax.get_yaxis().set_major_formatter(plt.LogFormatter(10,  labelOnlyBase=False))
  plt.show()
  </code></pre>