title: histogram graph line style in matplotlib
body: <p>I need to plot two histograms in the same figure and there is overlapping. I use command like</p>
  
  <pre><code>plt.hist(data1,bins=40,normed=True,histtype='step')
  plt.hist(data2,bins=40,normed=True,histtype='step')
  </code></pre>
  
  <p>To distinguish these two different histograms (need to present them in black and white), I want to make one of them appear in dashed line instead of solid line, so I tried</p>
  
  <pre><code>plt.hist(data1,bins=40,normed=True,histtype='step',ls='--')
  </code></pre>
  
  <p>which gave me the following error message:</p>
  
  <pre><code>Exception in Tkinter callback
  Traceback (most recent call last):
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/tkinter/__init__.py", line 1475, in __call__
      return self.func(*args)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/tkinter/__init__.py", line 534, in callit
      func(*args)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/backends/backend_tkagg.py", line 363, in idle_draw
      self.draw()
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/backends/backend_tkagg.py", line 348, in draw
      FigureCanvasAgg.draw(self)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/backends/backend_agg.py", line 451, in draw
      self.figure.draw(self.renderer)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/artist.py", line 56, in draw_wrapper
      draw(artist, renderer, *args, **kwargs)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/figure.py", line 1035, in draw
      func(*args)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/artist.py", line 56, in draw_wrapper
      draw(artist, renderer, *args, **kwargs)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/axes.py", line 2088, in draw
      a.draw(renderer)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/artist.py", line 56, in draw_wrapper
      draw(artist, renderer, *args, **kwargs)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/patches.py", line 401, in draw
      gc.set_linestyle(self._linestyle)
    File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/backend_bases.py", line 962, in set_linestyle
      raise ValueError('Unrecognized linestyle: %s' % str(style))
  ValueError: Unrecognized linestyle: --
  </code></pre>
  
  <p>My question is, how can I change the line style (solid/dashed and color)? Or is there an alternative way to plot these two histograms with desired line styles?</p>