Python2 - 37#

g=lambda x:(x%4or x%400and x%100<1)<1

Note that if a is a nonnegative integer, then a<1 is a short way of writing not bool(a). The last <1 thus effectively converts the expression in the parentheses to a boolean and negates the result.

Applying the function g to an integer n between 1801 and 2400 will return True if n is a leap year, and False otherwise.