Python: How to update value of key value pair in nested dictionary?

Question

i am trying to make an inversed document index, therefore i need to know from all unique words in a collection in which doc they occur and how often.

i have used this an

Answer 1

if (word == keyword and dictionary[keyword][filename] is not None): 

that is not a correct usage i guess, instead try this:

if (word == keyword and filename in dictionary[keyword]): 

Because, checking the value of a non-existing key raise KeyError. :so You must check if key exists in dictionary...