Newby Question: Python and A Nested Dictionary

[kbass]

I am new to Python and I am attempting to retrieve data from a database and
I would like to place this data into a nested dictionary. After placing the
data into a dictionary, I would like to loop through the data using for
loops. How would I do this? The format that I am attempting is:

Select data ...
Get data ...
Place data into a nested dictionary
     Rev[A] [B] = [500, 700, ...]
for value1 in a:
   for value2 in Rev[A]
      for value3 in Rev[A][B]
         print something

kbass