Check for dict key existence, and modify it in one step.

[rodrigo]

Im using this construct a lot:

if dict.has_key(whatever):
    dict[whatever] += delta
else:
    dict[whatever] = 1

sometimes even nested:

if dict.has_key(whatever):
    if dict[whatever].has_key(someother):
        dict[whatever][someother] += delta
    else:
        dict[whatever][someother] = 1
else:
    dict[whatever]={}
    dict[whatever][someother] = 1

there must be a more compact, readable and less redundant way to do
this, no?

Thanks,

Rodrigo