"""
function1:
inputs: num1, num2, should be integers, with num1 <= num2
output: the list of all even numbers between a and b
error handling: returns None if input requirements are violated.
"""
def function1(num1, num2):
    if (not(type(num1) is int)) or (not(type(num2) is int)):
        return []
    if (num1 > num2):
        return []
    
    result = []
    for var in range(num1, num2+1):
        if (var % 2 == 0):
            result.append(var)
    return result

a = 4
b = 9
c = function1(a, b)
print(c)

a = 100
b = 200
c = function1(a, b)
print(c)