Comment says the string needs to be returned when the grader expects it to be printed.

def print_full_name(first, last): print("Hello",first+" "+last+"! You just delved into python.")

def print_full_name(first, last): # Write your code here print(f"Hello {first} {last}! You just delved into python.")

print(f"Hello {first} {last}! You just delved into python.")

For Python3 Platform

def print_full_name(first, last):
    print("Hello", first, last+"!", "You just delved into python.")

if __name__ == '__main__':
    first_name = input()
    last_name = input()
    print_full_name(first_name, last_name)