It's straight from the definition of an integer. An integer is defined as sum(i=0 to n) d_n * base^n. A number with zero digits is just the empty sum, which is

It's straight from the definition of an integer. An integer is defined as sum(i=0 to n) d_n * base^n. A number with zero digits is just the empty sum, which is canonically defined to be zero. I'll also note that int() returns 0.