When using the pdf backend adding an axvspan causes an error. The full traceback is below:

File "run.py", line 27, in
experiment.savePlots('/home/mersoj/Documents/', 'multiPlots')
File "/home/mersoj/Documents/Research/forceanalysis_update/experiment.py", line 175, in savePlots
bbox_inches='tight')
File "/usr/lib/python3.3/site-packages/matplotlib/figure.py", line 1371, in savefig
self.canvas.print_figure(_args, *_kwargs)
File "/usr/lib/python3.3/site-packages/matplotlib/backend_bases.py", line 2055, in print_figure
*_kwargs)
File "/usr/lib/python3.3/site-packages/matplotlib/backend_bases.py", line 1848, in print_pdf
return pdf.print_pdf(_args, *_kwargs)
File "/usr/lib/python3.3/site-packages/matplotlib/backends/backend_pdf.py", line 2301, in print_pdf
self.figure.draw(renderer)
File "/usr/lib/python3.3/site-packages/matplotlib/artist.py", line 55, in draw_wrapper
draw(artist, renderer, *args, *_kwargs)
File "/usr/lib/python3.3/site-packages/matplotlib/figure.py", line 1007, in draw
func(_args)
File "/usr/lib/python3.3/site-packages/matplotlib/artist.py", line 55, in draw_wrapper
draw(artist, renderer, *args, *_kwargs)
File "/usr/lib/python3.3/site-packages/matplotlib/axes.py", line 2088, in draw
a.draw(renderer)
File "/usr/lib/python3.3/site-packages/matplotlib/artist.py", line 55, in draw_wrapper
draw(artist, renderer, _args, *_kwargs)
File "/usr/lib/python3.3/site-packages/matplotlib/patches.py", line 442, in draw
renderer.draw_path(gc, tpath, affine, rgbFace)
File "/usr/lib/python3.3/site-packages/matplotlib/backends/backend_pdf.py", line 1520, in draw_path
self.file.output(self.gc.paint())
File "/usr/lib/python3.3/site-packages/matplotlib/backends/backend_pdf.py", line 2032, in paint
return Op.paint_path(False, self.fillp(), self.strokep())
File "/usr/lib/python3.3/site-packages/matplotlib/backends/backend_pdf.py", line 2002, in strokep
return (self._linewidth > 0 and self._alpha > 0 and
TypeError: unorderable types: str() > int()