def func1():
    print(666)

def func2():
    print(777)
    def func3():
        func1()
        print(888)
    print(111)
    func3()
    print(333)
func2()

# 1，函数名可以作为变量。
def func1():
    print(111)
ret = func1
ret()

# 2,函数名可以作为函数的参数

def func2():
    print(666)

def func3(x):
    x()
func3(func2)

# 3,函数名可以作为容器类类型的元素
def func1():
    print(666)

def func2():
    print(666)

def func3():
    print(666)

l1 = [func1,func2,func3]
for i in l1:
    i()

# 函数名可以作为函数的返回值

def func1():
    print(666)

def func2(x):
    print(888)
    return x

ret = func2(func1)
ret()

# 第一种
def func():
    def func2():
        print(333)
    func2()
func()

# 第二种
def func():
    def func2():
        print(333)
    return func2  #func2 = func()   func2() ==func()()
func()()   #  func()() =func2()

# 增加ret
def func():
    def func2():
        print(333)
    return func2  #func2 = func()   func2() ==func()()
ret = func()   #ret = func() = func2
ret()   #ret() = func2()
func()()   #  func()() =func2()