Python: Calculate score of each pair for WordPiece algorithm

Question

I have a dictionary, splits, as follows:

{'A': ['A'],
 'man': ['m', '##a', '##n'],
 '’': ['’'],
 's': ['s'],
 'favorite': ['f', '##a', '##v', '##o', '##r', '##i', '##t', '##e'],
 'donkey': ['d', '##o', '##n', '##k', '##e', '##y'],
 'falls': ['f', '##a', '##l', '##l', '##s'],
 'into': ['i', '##n', '##t', '##o'],
 'a': ['a']}

I'm trying to implement WordPiece algorithm and need to compute the score of each pair using the formula:

score = frequency of pair / (frequency of first element * frequency of second element)

frequency of pair: number of times the pair has occurred in the splits.
frequency of first element: number of times the first element has occurred.
frequency of second element: number of times the second element has occurred.

The output need to be as follows:

The problem is I can't figure out how to separate individual pairs from the dictionary and then count their instances. Can anybody help me please?

Thanks.