title: Error setting tick positions with matplotlib in python
body: <p>I'm trying to set tick mark positions in matplotlib. I get errors when running the following minimal example:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  import numpy as np
  from matplotlib.ticker import MultipleLocator
  
  x = 10.*np.random.randn(1000)
  y = 10.*np.random.randn(1000)
  
  fig = plt.figure()
  ax = fig.add_subplot(1,1,1)
  ax.scatter(x, y)
  ax.xaxis.set_major_formatter(MultipleLocator(1.))
  ax.yaxis.set_major_formatter(MultipleLocator(1.))
  plt.show()
  </code></pre>
  
  <p>The error lies with the two lines that set the x- and y-axis tick marks. If I use NullFormatter() instead, or omit these lines entirely, the code runs fine and produces the expected plot. The above code, however, returns the following error:</p>
  
  <pre><code>Exception in Tkinter callback
  Traceback (most recent call last):
    File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1413, in __call__
      return self.func(*args)
    File "/usr/lib/pymodules/python2.7/matplotlib/backends/backend_tkagg.py", line 245, in resize
      self.show()
    File "/usr/lib/pymodules/python2.7/matplotlib/backends/backend_tkagg.py", line 248, in draw
      FigureCanvasAgg.draw(self)
    File "/usr/lib/pymodules/python2.7/matplotlib/backends/backend_agg.py", line 394, in draw
      self.figure.draw(self.renderer)
    File "/usr/lib/pymodules/python2.7/matplotlib/artist.py", line 55, in draw_wrapper
      draw(artist, renderer, *args, **kwargs)
    File "/usr/lib/pymodules/python2.7/matplotlib/figure.py", line 798, in draw
      func(*args)
    File "/usr/lib/pymodules/python2.7/matplotlib/artist.py", line 55, in draw_wrapper
      draw(artist, renderer, *args, **kwargs)
    File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 1946, in draw
      a.draw(renderer)
    File "/usr/lib/pymodules/python2.7/matplotlib/artist.py", line 55, in draw_wrapper
      draw(artist, renderer, *args, **kwargs)
    File "/usr/lib/pymodules/python2.7/matplotlib/axis.py", line 971, in draw
      tick_tups = [ t for t in self.iter_ticks()]
    File "/usr/lib/pymodules/python2.7/matplotlib/axis.py", line 906, in iter_ticks
      self.major.formatter.set_locs(majorLocs)
  AttributeError: MultipleLocator instance has no attribute 'set_locs'
  </code></pre>
  
  <p>I've tried googling this error, but I can't find anyone else who has a similar problem. Any ideas as to why the use of locators is yielding errors?</p>