SVN revision 4909 seems to have broken the YAArrow constructor by changing its dpi parameter to be figure instead, while Artist's constructor sets self.figure to None. Since YAArrow.__init__ calls the Patch constructor after setting self.figure, and the Patch constructor calls the Artist constructor, the constructed YAArrow object ends up with self.figure == None.

This causes YAArrow patches to not be usable in a PatchCollection because that constructor calls get_path, which attempts to access the YAArrow's dpi from the figure member:

    p = PatchCollection(patches, match_original=True)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/collections.py", line 1125, in __init__
    self.set_paths(patches)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/collections.py", line 1129, in set_paths
    for p in patches]
  File "/usr/local/lib/python2.7/site-packages/matplotlib/patches.py", line 1039, in get_path
    k1 = self.width*self.figure.dpi/72./2.
AttributeError: 'NoneType' object has no attribute 'dpi'

To work around the issue, it suffices to simply set the figure manually after constructing the YAArrow:

arrow = YAArrow(figure, (x,y), (x+dx, y+dy))
arrow.figure = figure

(For a diff of SVN revision 4909, see http://www.mail-archive.com/[email protected]/msg01214.html )

I'm using version 1.1.1~rc1+git20120423-0ubuntu1, but from scanning the source on github it looks as though the bug is still present.