Help with dictionary, please

[rbl at hal.cwru.edu]

I'm rapidly trying to learn Python and despite reading the documentation
and the "Learning Python" book, I can't figure out how to do the following:

-  I want to have a 2-dimensional array of word counts, indexed by
	a pair of words.  I.e.  dict[word1,word2]
-  In C, I'd just create a 2-dimensional array of integers and increment
	as required, but would have to hash the words into integer indices.

-  I tried the following in Python:
	dict = {}
	prev1 = ''
	prev2 = ''
[snip]

	if prev1 != '' and prev2 != '':
	 	   key = (prev2,prev1)
	           dict[key] = dict[key] + 1
   and got this error:
	  File "Metro:Python 1.5.1:learn2.py", line 34
          dict[key] = dict[key] + 1
                         ^
	SyntaxError: invalid token

I'm obviously missing something here!

Any guidance greatly appreciated!

Thank you,
Rob Lake
rbl at hal.cwru.edu