input: Write a function to calculate the sum of two numbers and print the result.
  assert calculate_sum(10, 20) == "sum is 30"
  assert calculate_sum(5, 15) == "sum is 20"
  assert calculate_sum(7, 13) == "sum is 20"
output: def calculate_sum(a, b):
      total = a + b
      return f"sum is {total}"