Exercise 7: Zero-Padded IDs — Possible Solution
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ids = [7, 42, 391, 5]

for ticket_id in ids:
    print(f"Ticket #{ticket_id:04d}")

Output:
Ticket #0007
Ticket #0042
Ticket #0391
Ticket #0005

WHY THIS WORKS AS AN ANSWER
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:04d means "format this as a decimal integer (d), padded with leading
ZEROS (the 0 flag) to a total width of 4 digits." Zero-padding is the
right choice here specifically because these are IDs, not counts or
free-form numbers — a ticket number is conventionally shown with a
fixed digit count, so "0007" reads as "ticket number seven" rather
than looking like the number seven thousand with digits missing. The
same width used with a plain space-padding specifier (:4d) would
produce "   7" instead, which doesn't read as a proper ID format.