1、

>>> def a():
    print("hello world!")

    
>>> a
<function a at 0x000002CE49DCB550>
>>> a()
hello world!

 

2、

>>> def a():
    print("hello world!")
    def b():
        print("xxxxxx!")
    return b

>>> a()
hello world!
<function a.<locals>.b at 0x0000020074A8F040>
>>> a()()
hello world!
xxxxxx!

 

3、

>>> def a():
    print("hello world!")
    def b():
        print("xxxxxx!")
    return b()

>>> a()
hello world!
xxxxxx!

 

小括号的作用表示执行函数。