is_leap(year) implementing the complete Gregorian rule: divisible by 4, except century years, unless divisible by 400. 1900 → False, 2000 → True. (calendar.isleap exists; write the logic yourself here.)is_leap(1900)
False
Century not divisible by 400.
is_leap(2000)
True
Divisible by 400.
(y % 4 == 0 and y % 100 != 0) or y % 400 == 0.
Test both example years.