what do i add to complete - python

An n -gram is a sequence of n letters. For example, bol and old are the two 3-grams that occur in the string bold . Write a function called count_ngrams () that counts the number of times each n -gram occurs in a string, with n specified by the user and with defau value n = 1 . You should be able to do this by making only a small modification to count_characters() . Example usage: count_ngrams ("tortoise", n = 2) {'to': 2, 'or': 1, 'rt': 1, 'oi': 1, 'is': 1, 'se': 1} # output Your Solution : = def count_ngrams (s, n=1): dict {} for i in range(len(s)): dict[s[i]] = 0 for i in range (len(s)): dict[s[i]] +=1 return dict count_ngrams ("tortoise" n = 2)