---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
~/anaconda2/envs/py36/lib/python3.6/site-packages/IPython/core/formatters.py in __call__(self, obj)
    330                 pass
    331             else:
--> 332                 return printer(obj)
    333             # Finally look for special method names
    334             method = get_real_method(obj, self.print_method)

~/anaconda2/envs/py36/lib/python3.6/site-packages/IPython/core/pylabtools.py in <lambda>(fig)
    235 
    236     if 'png' in formats:
--> 237         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs))
    238     if 'retina' in formats or 'png2x' in formats:
    239         png_formatter.for_type(Figure, lambda fig: retina_figure(fig, **kwargs))

~/anaconda2/envs/py36/lib/python3.6/site-packages/IPython/core/pylabtools.py in print_figure(fig, fmt, bbox_inches, **kwargs)
    119 
    120     bytes_io = BytesIO()
--> 121     fig.canvas.print_figure(bytes_io, **kw)
    122     data = bytes_io.getvalue()
    123     if fmt == 'svg':

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/backend_bases.py in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, **kwargs)
   2206                     orientation=orientation,
   2207                     dryrun=True,
-> 2208                     **kwargs)
   2209                 renderer = self.figure._cachedRenderer
   2210                 bbox_inches = self.figure.get_tightbbox(renderer)

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/backends/backend_agg.py in print_png(self, filename_or_obj, *args, **kwargs)
    505 
    506     def print_png(self, filename_or_obj, *args, **kwargs):
--> 507         FigureCanvasAgg.draw(self)
    508         renderer = self.get_renderer()
    509         original_dpi = renderer.dpi

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/backends/backend_agg.py in draw(self)
    428             if toolbar:
    429                 toolbar.set_cursor(cursors.WAIT)
--> 430             self.figure.draw(self.renderer)
    431         finally:
    432             if toolbar:

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     53                 renderer.start_filter()
     54 
---> 55             return draw(artist, renderer, *args, **kwargs)
     56         finally:
     57             if artist.get_agg_filter() is not None:

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/figure.py in draw(self, renderer)
   1293 
   1294             mimage._draw_list_compositing_images(
-> 1295                 renderer, self, artists, self.suppressComposite)
   1296 
   1297             renderer.close_group('figure')

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/image.py in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    136     if not_composite or not has_images:
    137         for a in artists:
--> 138             a.draw(renderer)
    139     else:
    140         # Composite any adjacent images together

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     53                 renderer.start_filter()
     54 
---> 55             return draw(artist, renderer, *args, **kwargs)
     56         finally:
     57             if artist.get_agg_filter() is not None:

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/axes/_base.py in draw(self, renderer, inframe)
   2397             renderer.stop_rasterizing()
   2398 
-> 2399         mimage._draw_list_compositing_images(renderer, self, artists)
   2400 
   2401         renderer.close_group('axes')

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/image.py in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    136     if not_composite or not has_images:
    137         for a in artists:
--> 138             a.draw(renderer)
    139     else:
    140         # Composite any adjacent images together

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     53                 renderer.start_filter()
     54 
---> 55             return draw(artist, renderer, *args, **kwargs)
     56         finally:
     57             if artist.get_agg_filter() is not None:

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/image.py in draw(self, renderer, *args, **kwargs)
    546         else:
    547             im, l, b, trans = self.make_image(
--> 548                 renderer, renderer.get_image_magnification())
    549             if im is not None:
    550                 renderer.draw_image(gc, l, b, im)

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/image.py in make_image(self, renderer, magnification, unsampled)
    772         return self._make_image(
    773             self._A, bbox, transformed_bbox, self.axes.bbox, magnification,
--> 774             unsampled=unsampled)
    775 
    776     def _check_unsampled_image(self, renderer):

~/anaconda2/envs/py36/lib/python3.6/site-packages/matplotlib/image.py in _make_image(self, A, in_bbox, out_bbox, clip_bbox, magnification, unsampled, round_to_pixel_border)
    368                 # old versions of numpy do not work with `np.nammin`
    369                 # and `np.nanmax` as inputs
--> 370                 a_min = np.ma.min(A).astype(scaled_dtype)
    371                 a_max = np.ma.max(A).astype(scaled_dtype)
    372                 # scale the input data to [.1, .9].  The Agg

~/anaconda2/envs/py36/lib/python3.6/site-packages/numpy/ma/core.py in astype(self, newtype)
   3203                 output._mask = self._mask.astype([(n, bool) for n in names])
   3204         # Don't check _fill_value if it's None, that'll speed things up
-> 3205         if self._fill_value is not None:
   3206             output._fill_value = _check_fill_value(self._fill_value, newtype)
   3207         return output

AttributeError: 'MaskedConstant' object has no attribute '_fill_value'