The inner function and the explanatory comment it makes necessary can
all be removed if we switch to an if/else rather than try/except for
this condition.
Perhaps this bit comes from my fondness for C, but I think I would
find this style clearer and easier to understand even if it weren't
for the Python 2 quirk that makes the other style require us to add an
unnecessary-looking function abstraction. In any case, given that the
alternative does require that abstraction this is definitely simpler.
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