---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-99968ca80698> in <module>
     10                                        arrowstyle='-|>', mutation_scale=10,
     11                                        facecolor='k', clip_on=False)
---> 12 ax.add_patch(arrow)

~/github/matplotlib/lib/matplotlib/axes/_base.py in add_patch(self, p)
   1965         if p.get_clip_path() is None:
   1966             p.set_clip_path(self.patch)
-> 1967         self._update_patch_limits(p)
   1968         self.patches.append(p)
   1969         p._remove_method = self.patches.remove

~/github/matplotlib/lib/matplotlib/axes/_base.py in _update_patch_limits(self, patch)
   1983                 ((not patch.get_width()) and (not patch.get_height()))):
   1984             return
-> 1985         vertices = patch.get_path().vertices
   1986         if vertices.size > 0:
   1987             xys = patch.get_patch_transform().transform(vertices)

~/github/matplotlib/lib/matplotlib/patches.py in get_path(self)
   4239         in display coordinates.
   4240         """
-> 4241         _path, fillable = self.get_path_in_displaycoord()
   4242 
   4243         if np.iterable(fillable):

~/github/matplotlib/lib/matplotlib/patches.py in get_path_in_displaycoord(self)
   4254 
   4255         if self._posA_posB is not None:
-> 4256             posA = self.get_transform().transform_point(self._posA_posB[0])
   4257             posB = self.get_transform().transform_point(self._posA_posB[1])
   4258             _path = self.get_connectionstyle()(posA, posB,

~/github/matplotlib/lib/matplotlib/transforms.py in transform_point(self, point)
   1517         if len(point) != self.input_dims:
   1518             raise ValueError("The length of 'point' must be 'self.input_dims'")
-> 1519         return self.transform(np.asarray([point]))[0]
   1520 
   1521     def transform_path(self, path):

~/github/matplotlib/lib/matplotlib/transforms.py in transform(self, values)
   1430 
   1431         # Transform the values
-> 1432         res = self.transform_affine(self.transform_non_affine(values))
   1433 
   1434         # Convert the result back to the shape of the input values.

~/github/matplotlib/lib/matplotlib/transforms.py in transform_affine(self, points)
   2416 
   2417     def transform_affine(self, points):
-> 2418         return self.get_affine().transform(points)
   2419     transform_affine.__doc__ = Transform.transform_affine.__doc__
   2420 

~/github/matplotlib/lib/matplotlib/transforms.py in transform(self, values)
   1745 
   1746     def transform(self, values):
-> 1747         return self.transform_affine(values)
   1748     transform.__doc__ = Transform.transform.__doc__
   1749 

~/github/matplotlib/lib/matplotlib/transforms.py in transform_affine(self, points)
   1829             tpoints = affine_transform(points.data, mtx)
   1830             return np.ma.MaskedArray(tpoints, mask=np.ma.getmask(points))
-> 1831         return affine_transform(points, mtx)
   1832 
   1833     def transform_point(self, point):

TypeError: Cannot cast array data from dtype('O') to dtype('float64') according to the rule 'safe'