function advanced function of Python basis as return value/adorner

Because the adorner needs to use the knowledge of the return function, the return function and adorner are explained here.

What is a return function?

We know that in a function, return can return one or more values, but in fact, return can return not only the value, but also the function.

Instance:

defCol (*Arg):defsum (): Res_sum=0 forIinchArg:res_sum=res_sum+IreturnRes_sumreturnSuma=col (1,2,3,4,5)Print(a)
<function Col.<locals>.sum at 0x029102b8>
#A=col (1,2,3,4,5) ==〉#that is a=sum, and arg= (1,2,3,4,5) is also passed into sum.#A () ==sum ()

and because sum () is defined in the col () function, sum () inherits the local variables and arguments of the col () function, which is the closure . (for example, the arg parameter of Col () is inherited by sum ())

Let's look at a question I encountered when I checked the above red sentence:

#or use the code above. Change it a little bit.defCol (*Arg): res_sum =0         #Note: Move this word here.    defsum (): forIinchArg:res_sum=res_sum+IreturnRes_sumreturnSuma=col (1,2,3,4,5)Print(A ()) result error: local variable'Res_sum'referenced before assignment#since intrinsic functions can refer to variables of external functions, why is res_sum not referenced by the # part function? 

Why did you get an error? I was puzzled at the time and finally figured it out, wrong in this sentence:res_sum=res_sum+I This sentence causes the internal function to modify the external function of the local variables, and this is not allowed!!!!

Therefore, this modification is required:

def Col (*Arg):    res_sum=0             def  sum ():        for in  ARG:            a=res_sum+i     # defines a new variable a        in the intrinsic function return a     return suma=col (1,2,3,4,5)print(A ())

What is an adorner?

def login ():     Pass @login       #关键字 @  def open ():     Pass

The example above is an example of an adorner.

The role of adorners:

After we have defined the Open function (which can help us to open a file), after a while, we find that we need to verify the user before the open, how to combine the login function and the open function without modifying the Open function , That is: Run login before running open? The decorator will be used here.

Let's see an example of a real decorator:

def Login (Fun):     def Real_login ():         Print ('pleaseinput your password')         return Fun ()     return Real_login@login def open ():     Print ('helloworld') open ()

@login is equivalent to Open=login (open), which rescue the open function.

When we run open ():

open=Login (Open)
　　Parameters and local variables in the #login (open): Fun=open (original)
　　# The return value of Open=login (open)!  #即:open=real_login 
　　
Open () =real_login ()  # because real_login is defined in login, it inherits its arguments and local variables # so look at the whole open ( ) ==login (Open) +real_login () +open ()

function advanced function of Python basis as return value/adorner