Exercise 4: Linear Search Through a Tuple — Possible Solution
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colours = ("red", "green", "blue", "yellow", "purple")
target = input("Enter a colour to search for: ")

index = 0
found_at = -1

while index < len(colours):
    if colours[index] == target:
        found_at = index
        break
    index += 1

if found_at == -1:
    print("Not found")
else:
    print(f"Found at index {found_at}")

Example run (target = "blue"):
Found at index 2

Example run (target = "orange"):
Not found

WHY THIS WORKS AS AN ANSWER
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found_at starts at -1, a value that can never be a genuine index, so it
doubles as both "not found yet" and, at the end, "never found at all."
This avoids the tempting-but-wrong shortcut of checking "if found_at:"
as a boolean — index 0 is a perfectly valid match, but 0 is falsy in
Python, so a naive truthiness check would incorrectly treat "found at
index 0" the same as "not found." Comparing explicitly against -1 sidesteps
that trap entirely.

break exits the loop the moment a match is found, so the search doesn't
keep scanning colours that come after the match — the same early-exit
principle used in the lesson's case study and in Exercise 6.