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1. Spot the bug. This program crashes. What is the cause? ``

python
grid = [[0] * 3 for _ in range(2)]
for r in range(len(grid) + 1):
    for c in range(len(grid[r])):
        grid[r][c] = 1
print("filled")

``

The row loop uses + 1, so r reaches 2 and grid[2] does not exist in a grid with 2 rowsThe inner loop should use len(grid) instead of len(grid[r]), which would give too few columnsThe list should be built as [[0] * 2 for _ in range(3)]The print runs before the grid is filled

2. What does this program print? ``

python
w = [5, 5, 7, 2]
rises = 0
for i in range(len(w) - 1):
    if w[i + 1] > w[i]:
        rises += 1
print("Rises:", rises)

``

Rises: 0Rises: 2Rises: 3Rises: 1

3. Spot the bug. The program is meant to print the third day, Wed, but it crashes with IndexError: list index out of range. What is the cause? ``

python
days = ["Mon", "Tue", "Wed"]
day = 3
print(days[day])

``

The list needs a fourth name, because day 3 is the fourth dayDay numbers start at 1 but indexes start at 0, so days[3] is past the last index 2; use days[day - 1]Use len(days) instead of day, so the last name is readThe day should be the string "3", so Python reads the name

4. Which statement about the length of a list and a string is true?

Lists and strings both count with .size()arr.length() returns -1 for a listlen(arr) is the way to count a list, and arr.length raises an AttributeErrorarr.length is the way to count a list, and len(arr) raises an error

5. Spot the bug. The program should print the last value, but it crashes with IndexError: list index out of range. What fixes it? ``

python
arr = [4, 8, 15, 16, 23]
last = arr[len(arr)]
print(last)

``

The index should be len(arr) - 1, because the last valid index is 4 for a length of 5The list needs a sixth value so that index 5 existsUse arr.length - 1 instead, because length is an attributelast must be a float to hold the value 23

Bounds debugging