We're back after a server migration that caused effbot.org to fall
over a bit harder than expected. Expect some glitches.
a.setdefault(k[, x]) a[k] if k in a, else x (also setting it).
dict.setdefault is like dict.get, except that if k is missing,
x is both returned and inserted into the dictionary as the value of
k. x defaults to None.