How to programmatically exit without Traceback?

[Mark17]

This code ends by printing 4:

import sys

for i in range(10):
    if i == 5:
          sys.exit(0)
    print(i)

When I enter sum_two(3.5,6), the following prints "SystemExit" and then "UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.
warn("To exit: use 'exit', 'quit', or Ctrl-D.", stacklevel=1)":

print()
print('The function sum_two(a,b) will sum integers a and b.')
print('If sum is between 15 to 20 then output will be 20.')

def sum_two(a,b):
    if type(a) != int or type(b) != int:
        print('a and b must both be integers.')
        sys.exit()
    if a+b > 15 and a+b < 20:
        sum = 20
    else: sum = a+b
    return sum

Why doesn't the latter give me a clean exit like the former? Thanks!