input: Write a python function to print a greeting message. If the name is provided, it should print "Hello, {name}!". If no name is provided, it should print "Hello World".
  assert greet() == "Hello World"
  assert greet("John") == "Hello, John!"
  assert greet("Alice") == "Hello, Alice!"
output: def greet(name=None):
      if name:
          return f"Hello, {name}!"
      else:
          return "Hello World"