为什么用print会有none，而直接调用方法则不会有

第一种：
class User:
def init(self, first_name, last_name):
self.first = first_name
self.last = last_name

def greet_user(self):
    print(f"Hello, {self.first} {self.last}!How are you?")
    print('\n')

第二种：
user = User('kai', 'hu')
print(user.greet_user())

class User:
def init(self, first_name, last_name):
self.first = first_name
self.last = last_name

def greet_user(self):
    print(f"Hello, {self.first} {self.last}!How are you?")
    print('\n')

user = User('kai', 'hu')
user.greet_user()

你这个方法又没有返回值, 默认返回值就是None