Lesson 6

There are many programs that will not halt after being executed:

while True:
    pass

from itertools import count

for n in count():
    a = 2 * n

n = 3
while n < 7:
    if n > 5:
        n = 0
    n += 1

def binary_search(xs, key):
    lower, upper = 0, len(xs) - 1
    while lower < upper:
        middle = (lower + upper) // 2
        if xs[middle] == key:
            return middle
        elif xs[middle] < key:
            lower = middle
        else:
            upper = middle - 1

    return -1


print(binary_search([-4, -2, 1, 7, 12, 29], 17))

For the first three programs, it is immediately clear that they will loop indefinitely. However, finding and fixing the bug in the last program will take some time.