In [1]: import matplotlib.pyplot as plt

In [2]: plt.bar([1, 2, 3], [2, 3, 2], label='label')
Out[2]: 
[<matplotlib.patches.Rectangle at 0x1043415d0>,
 <matplotlib.patches.Rectangle at 0x104341650>,
 <matplotlib.patches.Rectangle at 0x104341ad0>]

In [3]: l = plt.legend()

In [4]: l.draggable()
Out[4]: <matplotlib.legend.DraggableLegend at 0x10434fbd0>

  File "/Users/sin/Library/Python/2.7/lib/python/site-packages/matplotlib/offsetbox.py", line 376, in get_extent_offsets
    whd_list = [c.get_extent(renderer) for c in self.get_visible_children()]
  File "/Users/sin/Library/Python/2.7/lib/python/site-packages/matplotlib/offsetbox.py", line 639, in get_extent
    "lp", self._text._fontproperties, ismath=False)
  File "/Users/sin/Library/Python/2.7/lib/python/site-packages/matplotlib/backends/backend_macosx.py", line 161, in get_text_width_height_descent
    width, height, descent = self.gc.get_text_width_height_descent(unicode(s), family, size, weight, style)
RuntimeError: CGContextRef is NULL

Traceback (most recent call last):
  File "/Users/sin/Library/Python/2.7/lib/python/site-packages/matplotlib/backend_bases.py", line 1588, in motion_notify_event
    self.callbacks.process(s, event)
  File "/Users/sin/Library/Python/2.7/lib/python/site-packages/matplotlib/cbook.py", line 262, in process
    proxy(*args, **kwargs)
  File "/Users/sin/Library/Python/2.7/lib/python/site-packages/matplotlib/cbook.py", line 188, in __call__
    return mtd(*args, **kwargs)
  File "/Users/sin/Library/Python/2.7/lib/python/site-packages/matplotlib/offsetbox.py", line 1434, in on_motion
    self.update_offset(dx, dy)
  File "/Users/sin/Library/Python/2.7/lib/python/site-packages/matplotlib/offsetbox.py", line 1504, in update_offset
    loc_in_canvas = self.offsetbox_x + dx, self.offsetbox_y + dy
AttributeError: 'DraggableLegend' object has no attribute 'offsetbox_x'