(year)
return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)
year -> 1 if leap year, else 0.
year -> 1 if leap year, else 0.
year - > 1 if leap year else 0 .
def _is_leap(year):
    "year -> 1 if leap year, else 0."
    return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)
def _is_leap ( year ) : return year % 4 == 0 and ( year % 100 != 0 or year % 400 == 0 )