Programming with Python: Additional Exercises

A collection of exercises that have been either removed from or not (yet) added to the main lesson.

Swapping the contents of variables (5 min)

Explain what the overall effect of this code is:

left = 'L'
right = 'R'

temp = left
left = right
right = temp

Compare it to:

left, right = [right, left]

Do they always do the same thing? Which do you find easier to read?

Solution

Both examples exchange the values of left and right:

print(left, right)

R L

In the first case we used a temporary variable temp to keep the value of left before we overwrite it with the value of right. In the second case, right and left are packed into a list and then unpacked into left and right.

Fixing and Testing

From: “Defensive Programming”

Fix range_overlap. Re-run test_range_overlap after each change you make.

Solution

def range_overlap(ranges):
    '''Return common overlap among a set of [left, right] ranges.'''
    if not ranges:
        # ranges is None or an empty list
        return None
    max_left, min_right = ranges[0]
    for (left, right) in ranges[1:]:
        max_left = max(max_left, left)
        min_right = min(min_right, right)
    if max_left >= min_right:  # no overlap
        return None
    return (max_left, min_right)