a. extract_num(s, begin, end) The trickiest part of this problem is this: we have found one or more digits in a string, and we need to extract that number properly or decide to omit it. The extract_num() function is decomposed out to focus on that sub-problem. def extract_num(s, begin, end) : Given string s, and "begin" is the index of the first of one or more digits, and "end" is the index one beyond the last digit. Parse out and return the int value of the number, accounting for possible 's' and '*'. Return -1 if the number should be skipped. >>> extract_num('xx123$', 2, 5) 321 One test is provided. Add tests so there are at least five tests. Test varying numbers of digits, with and without' and 'S'. It is easier to build and perfect extract_num in isolation here vs. in the midst of processing a whole file. edef extract nuns, begin, end): # Given string s, and "begin" is the index of the first of one or more digits, and "end" is the index one beyond the last digit. Parse out and return the int value of the number, accounting for possible "s' and a. Return -1 if the number should be skipped. extract_nun("xx123$ 2, 5) 321 >>> # add Doctests here and in, $', 2, 99 be skipped pass