how do I do this using python?

" Define the get_ previous_words_dict0 function which is passed a string of text as a parameter. The function retums a dictionary with keys which are all the unique words from the text, and cormesponding values which are lists of all the unique words in the text which come before the key word. Note that in each corresponding list of previous words the same word should not appear more than once Notes the first word in the sentence will initially have the empty string as its previous word. you can assume that the text is all in lower case and contains no punctuation, each list of previous words must be sorted into ascending order the testing code makes use of the print dict n_key ordena dict) which prints the dictionary pairs in sorted key order . . For example, the following code text 'a man we saw saw a saw previous_words_dict get_previous_words_dict(text) print dict_in_key_order(previous_words_dict) print) text- 'my favourite painting is the painting i did of my dog in that painting in my den previous_words_dict get_previous_words_dict(text) print dict_in_key_order(previous_words_dict) prints man: ['a saw :?a, den: ['my' did : ['i'] dog ['y' favourite ['my' i'painting' in ['dog, 'painting'] is ['painting my:[in 'of of : ['did' painting 'favourite, 'that', the] that ['in' the : ['is