CSc 120: Assert: Evens and Odds 1

Expected Behavior

The following function takes a list arglist and returns a pair of lists, evens and odds, such that evens consists of the elements at even-numbered positions of arglist, i.e., arglist[0], arglist[2], etc.; and odds consists of the elements at odd-numbered positions of arglist, i.e., arglist[1], arglist[3], etc.

def odds_and_evens(arglist):
    evens = []
    odds = []
    for i in range(len(arglist)):
        ith_element = arglist[i]

        if i % 2 == 0:
            evens.append(ith_element)
        else:
            odds.append(ith_element)

        assert ith_element_is_in_correct_list(arglist, i, evens, odds)

    return (evens,odds)

Write a function ith_element_is_in_correct_list(arglist, i, evens, odds) that will be called by the assert at the end of each iteration of the loop shown above. The purpose of this function is to check that the i^th element has been inserted into the right one of the two lists odds and evens.

Your function ith_element_is_in_correct_list(arglist, i, evens, odds) should behave as follows. Given:

• arglist: the list being split into even- and odd-position lists;
• i: the current value of the loop index;
• evens and odds: the lists of even- and odd-position elements of arglist, respectively, up to (and including) the current iteration of the loop;

returns:

• True if the i^th element of arglist has been inserted into the end of the correct one of the two lists evens and odds depending on whether the value of i is even or odd.
• False otherwise.

Programming Requirements

Note that solutions that "accidentally" pass test cases will not get credit.

Examples

In the examples below, arglist = ['aa','bb','cc','dd','ee','ff','gg','hh','ii'].

1. Call: ith_element_is_in_correct_list(arglist, 0, ['aa'], [])
   Return value: True

2. Call: ith_element_is_in_correct_list(arglist, 0, ['aa'], [123,456,789])
   Return value: True

3. Call: ith_element_is_in_correct_list(arglist, 1, [], [123,456,'bb'])
   Return value: True

4. Call: ith_element_is_in_correct_list(arglist, 2, ['aa','cc','ee'], [123,456,'bb'])
   Return value: False

5. Call: ith_element_is_in_correct_list(arglist, 5, ['aa','cc','ee'], ['ff'])
   Return value: True

6. Call: ith_element_is_in_correct_list(arglist, 5, ['aa','cc'], ['ff', 'ee'])
   Return value: False