I just got done tracking down a bug in my code where I had a kwargs
dict with {'linewidth':'2'}. The problem was that this worked for
much of my code and didn't fail until I tried to save an eps:

/usr/lib/python2.4/site-packages/matplotlib/backends/ in
set_linewidth(self, linewidth, store)
    156 if linewidth != self.linewidth:
    157 print('linewidth='+str(linewidth))
--> 158 self._pswriter.write("%1.3f setlinewidth\n"%linewidth)
    159 if store: self.linewidth = linewidth

TypeError: float argument required

I think it would have made more sense for this to fail earlier. I
think this should raise an error:

I think it should either fail all the time or work all the time, and
it is probably too much work to make it work all the time.

Any thoughts?