func call inner func

def f1():
    def f2():
        print("I am in Level 2")
        return f3
    
    def f3():
        print("I am in Level 3")
        return f4
        
    def f4():
        print("I am in Level 4")
        return f1
        
    print("I am in Level 1")
    return f2
 
f1()()()()()