dictionary idiom needed

[Brandon]

Thanks bear -

Some outside advice has me looking at nested dictionaries.  But I am
still bogged down because I've not created one before and all examples
I can find are simple ones where they are created manually, not with
loops.  Maybe a further example:

data:
  POS1    POS2   POS3
['word1','tagA','tagB']
['word2','tagC','tagD']
['word1','tagE','tagB']
['word1','tagC','tagF']

... and so on.  FWIW:  I am guaranteed that the set of tags that may
occur in position2 is complementary to the set of tags that may occur
in position3.

Now I want to get an accounting of all the tags that occurred in
position3 in the context of, say, word1.  Here I've shown that for
word1, tagB and tagF occurs.  I want a way to access all this
information such that nested_dict['word1']['tagB'] = 2, and nested_dict
['word1']['tagF'] = 1.

As I mentioned, I already have dicts such that dictA['word1'] = 3, and
dictB['tagB'] = 2.  I used defaultdict to build those, and that seems
to be causing me to get some funky values back from my initial
attempts to build a nested dictionary.  I am stumbling at constructing
a "for" loop that automatically creates such nested dictionaries.

I hope that clears things up.  If you still have any advice, it's much
appreciated.

Thanks,

Brandon