dictionary with tuple keys

[Brandon Devine]

Hi all,

I am probably not thinking straight anymore about this problem.  I
have a dictionary with tuple keys in the format (a, b, A, B) and float
values.  I want to collect all the keys with identical (a, b...),
disregarding whatever (... A, B) might be.  Specifically, I want to
sum the float values once I've collected these keys.  I am staring at
my screen, pondering ugly things, and I just know I must be missing a
Pythonic solution.  Any suggestions?

Thanks for any help,

Brandon