The format
method requires you to pass your arguments as kwargs, not as a dictionary.
def __unicode__(self):
if self.right:
return u"{left} ({left_score}) | {right} ({right_score})".format(
left=self.left,
left_score=self.left_score,
right=self.right,
right_score=self.right_score,
)
else:
return "%s" % self.left