Understanding how does a decorator really work [duplicate]












1
















This question already has an answer here:




  • How to make a chain of function decorators?

    16 answers




I'm starting studying decorators and I already hit an obstacle. First here is my code.



 def deco (f):



    def coucou():

        print("this is function{}".format(f))

        return f()

    return coucou



@deco

def salut():

    print("salut")





def hi():

    return salut()


I will try to explain my problem as well as I can with my bad English. If I understand it this is how things should happen: I execute my hi() function which returns salut() and because salut is modified by the decorator coucou will be executed and coucou returns ....... salut(), what i mean is that I expect an infinite loop but that doesn't happen and I don't understand why. Can anyone explain practically how decorators work?






python python-3.x decorator







share|improve this question















marked as duplicate by Bazingaa, Noctis Skytower, Community♦ Jan 19 at 1:08


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.



















  • realpython.com/primer-on-python-decorators This may help in understanding how decorators work

    – Pro Q
    Jan 19 at 0:20











  • You may also want to have a look at the documentation: PEP-318 and PEP-3129.

    – Ondrej K.
    Jan 19 at 0:29
















1
















This question already has an answer here:




  • How to make a chain of function decorators?

    16 answers




I'm starting studying decorators and I already hit an obstacle. First here is my code.



 def deco (f):



    def coucou():

        print("this is function{}".format(f))

        return f()

    return coucou



@deco

def salut():

    print("salut")





def hi():

    return salut()


I will try to explain my problem as well as I can with my bad English. If I understand it this is how things should happen: I execute my hi() function which returns salut() and because salut is modified by the decorator coucou will be executed and coucou returns ....... salut(), what i mean is that I expect an infinite loop but that doesn't happen and I don't understand why. Can anyone explain practically how decorators work?






python python-3.x decorator







share|improve this question















marked as duplicate by Bazingaa, Noctis Skytower, Community♦ Jan 19 at 1:08


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.



















  • realpython.com/primer-on-python-decorators This may help in understanding how decorators work

    – Pro Q
    Jan 19 at 0:20











  • You may also want to have a look at the documentation: PEP-318 and PEP-3129.

    – Ondrej K.
    Jan 19 at 0:29














1












1








1









This question already has an answer here:




  • How to make a chain of function decorators?

    16 answers




I'm starting studying decorators and I already hit an obstacle. First here is my code.



 def deco (f):



    def coucou():

        print("this is function{}".format(f))

        return f()

    return coucou



@deco

def salut():

    print("salut")





def hi():

    return salut()


I will try to explain my problem as well as I can with my bad English. If I understand it this is how things should happen: I execute my hi() function which returns salut() and because salut is modified by the decorator coucou will be executed and coucou returns ....... salut(), what i mean is that I expect an infinite loop but that doesn't happen and I don't understand why. Can anyone explain practically how decorators work?






python python-3.x decorator







share|improve this question

















This question already has an answer here:




  • How to make a chain of function decorators?

    16 answers




I'm starting studying decorators and I already hit an obstacle. First here is my code.



 def deco (f):



    def coucou():

        print("this is function{}".format(f))

        return f()

    return coucou



@deco

def salut():

    print("salut")





def hi():

    return salut()


I will try to explain my problem as well as I can with my bad English. If I understand it this is how things should happen: I execute my hi() function which returns salut() and because salut is modified by the decorator coucou will be executed and coucou returns ....... salut(), what i mean is that I expect an infinite loop but that doesn't happen and I don't understand why. Can anyone explain practically how decorators work?





This question already has an answer here:




  • How to make a chain of function decorators?

    16 answers







python python-3.x decorator




python python-3.x decorator






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Jan 19 at 0:33









Ondrej K.

2,80361022




2,80361022










asked Jan 19 at 0:06









Newgate AceNewgate Ace

184




184




marked as duplicate by Bazingaa, Noctis Skytower, Community♦ Jan 19 at 1:08


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.









marked as duplicate by Bazingaa, Noctis Skytower, Community♦ Jan 19 at 1:08


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.















  • realpython.com/primer-on-python-decorators This may help in understanding how decorators work

    – Pro Q
    Jan 19 at 0:20











  • You may also want to have a look at the documentation: PEP-318 and PEP-3129.

    – Ondrej K.
    Jan 19 at 0:29



















  • realpython.com/primer-on-python-decorators This may help in understanding how decorators work

    – Pro Q
    Jan 19 at 0:20











  • You may also want to have a look at the documentation: PEP-318 and PEP-3129.

    – Ondrej K.
    Jan 19 at 0:29

















realpython.com/primer-on-python-decorators This may help in understanding how decorators work

– Pro Q
Jan 19 at 0:20





realpython.com/primer-on-python-decorators This may help in understanding how decorators work

– Pro Q
Jan 19 at 0:20













You may also want to have a look at the documentation: PEP-318 and PEP-3129.

– Ondrej K.
Jan 19 at 0:29





You may also want to have a look at the documentation: PEP-318 and PEP-3129.

– Ondrej K.
Jan 19 at 0:29












1 Answer
1






active

oldest

votes


















2














The f in coucou is the undecorated (original) version of salut.






share|improve this answer
























  • yeah but why and how? again if i got it, the decorator modify the function in its definition and makes it point permanently to the function returned by the decorator, am i wrong?

    – Newgate Ace
    Jan 19 at 0:13






  • 1





    @NewgateAce it doesn't modify the original function. It creates a new function, and returns a new function. So the global name salut now refers to the function returned by the decorator, i.e. coucou, but coucou's local name f, which is a free variable closed over by coucou, still refers to the original function

    – juanpa.arrivillaga
    Jan 19 at 0:16













  • @NewgateAce in other words, there is nothing magical about the decorator syntax. It is equivalent to def my_function(): ...; my_func = deco(my_func)

    – juanpa.arrivillaga
    Jan 19 at 0:24











  • @juanpa.arrivillaga i see now, f = deco(f) makes it clearer for me. thanks for your reply.

    – Newgate Ace
    Jan 19 at 0:30











  • @juanpa.arrivillaga what im about to say might be stupid, but when i print "salut" and "deco(salut)", they dont have the same reference ...

    – Newgate Ace
    Jan 19 at 0:46


















1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









2














The f in coucou is the undecorated (original) version of salut.






share|improve this answer
























  • yeah but why and how? again if i got it, the decorator modify the function in its definition and makes it point permanently to the function returned by the decorator, am i wrong?

    – Newgate Ace
    Jan 19 at 0:13






  • 1





    @NewgateAce it doesn't modify the original function. It creates a new function, and returns a new function. So the global name salut now refers to the function returned by the decorator, i.e. coucou, but coucou's local name f, which is a free variable closed over by coucou, still refers to the original function

    – juanpa.arrivillaga
    Jan 19 at 0:16













  • @NewgateAce in other words, there is nothing magical about the decorator syntax. It is equivalent to def my_function(): ...; my_func = deco(my_func)

    – juanpa.arrivillaga
    Jan 19 at 0:24











  • @juanpa.arrivillaga i see now, f = deco(f) makes it clearer for me. thanks for your reply.

    – Newgate Ace
    Jan 19 at 0:30











  • @juanpa.arrivillaga what im about to say might be stupid, but when i print "salut" and "deco(salut)", they dont have the same reference ...

    – Newgate Ace
    Jan 19 at 0:46
















2














The f in coucou is the undecorated (original) version of salut.






share|improve this answer
























  • yeah but why and how? again if i got it, the decorator modify the function in its definition and makes it point permanently to the function returned by the decorator, am i wrong?

    – Newgate Ace
    Jan 19 at 0:13






  • 1





    @NewgateAce it doesn't modify the original function. It creates a new function, and returns a new function. So the global name salut now refers to the function returned by the decorator, i.e. coucou, but coucou's local name f, which is a free variable closed over by coucou, still refers to the original function

    – juanpa.arrivillaga
    Jan 19 at 0:16













  • @NewgateAce in other words, there is nothing magical about the decorator syntax. It is equivalent to def my_function(): ...; my_func = deco(my_func)

    – juanpa.arrivillaga
    Jan 19 at 0:24











  • @juanpa.arrivillaga i see now, f = deco(f) makes it clearer for me. thanks for your reply.

    – Newgate Ace
    Jan 19 at 0:30











  • @juanpa.arrivillaga what im about to say might be stupid, but when i print "salut" and "deco(salut)", they dont have the same reference ...

    – Newgate Ace
    Jan 19 at 0:46














2












2








2







The f in coucou is the undecorated (original) version of salut.






share|improve this answer













The f in coucou is the undecorated (original) version of salut.







share|improve this answer












share|improve this answer



share|improve this answer










answered Jan 19 at 0:10









Scott HunterScott Hunter

33.3k74071




33.3k74071













  • yeah but why and how? again if i got it, the decorator modify the function in its definition and makes it point permanently to the function returned by the decorator, am i wrong?

    – Newgate Ace
    Jan 19 at 0:13






  • 1





    @NewgateAce it doesn't modify the original function. It creates a new function, and returns a new function. So the global name salut now refers to the function returned by the decorator, i.e. coucou, but coucou's local name f, which is a free variable closed over by coucou, still refers to the original function

    – juanpa.arrivillaga
    Jan 19 at 0:16













  • @NewgateAce in other words, there is nothing magical about the decorator syntax. It is equivalent to def my_function(): ...; my_func = deco(my_func)

    – juanpa.arrivillaga
    Jan 19 at 0:24











  • @juanpa.arrivillaga i see now, f = deco(f) makes it clearer for me. thanks for your reply.

    – Newgate Ace
    Jan 19 at 0:30











  • @juanpa.arrivillaga what im about to say might be stupid, but when i print "salut" and "deco(salut)", they dont have the same reference ...

    – Newgate Ace
    Jan 19 at 0:46



















  • yeah but why and how? again if i got it, the decorator modify the function in its definition and makes it point permanently to the function returned by the decorator, am i wrong?

    – Newgate Ace
    Jan 19 at 0:13






  • 1





    @NewgateAce it doesn't modify the original function. It creates a new function, and returns a new function. So the global name salut now refers to the function returned by the decorator, i.e. coucou, but coucou's local name f, which is a free variable closed over by coucou, still refers to the original function

    – juanpa.arrivillaga
    Jan 19 at 0:16













  • @NewgateAce in other words, there is nothing magical about the decorator syntax. It is equivalent to def my_function(): ...; my_func = deco(my_func)

    – juanpa.arrivillaga
    Jan 19 at 0:24











  • @juanpa.arrivillaga i see now, f = deco(f) makes it clearer for me. thanks for your reply.

    – Newgate Ace
    Jan 19 at 0:30











  • @juanpa.arrivillaga what im about to say might be stupid, but when i print "salut" and "deco(salut)", they dont have the same reference ...

    – Newgate Ace
    Jan 19 at 0:46

















yeah but why and how? again if i got it, the decorator modify the function in its definition and makes it point permanently to the function returned by the decorator, am i wrong?

– Newgate Ace
Jan 19 at 0:13





yeah but why and how? again if i got it, the decorator modify the function in its definition and makes it point permanently to the function returned by the decorator, am i wrong?

– Newgate Ace
Jan 19 at 0:13




1




1





@NewgateAce it doesn't modify the original function. It creates a new function, and returns a new function. So the global name salut now refers to the function returned by the decorator, i.e. coucou, but coucou's local name f, which is a free variable closed over by coucou, still refers to the original function

– juanpa.arrivillaga
Jan 19 at 0:16







@NewgateAce it doesn't modify the original function. It creates a new function, and returns a new function. So the global name salut now refers to the function returned by the decorator, i.e. coucou, but coucou's local name f, which is a free variable closed over by coucou, still refers to the original function

– juanpa.arrivillaga
Jan 19 at 0:16















@NewgateAce in other words, there is nothing magical about the decorator syntax. It is equivalent to def my_function(): ...; my_func = deco(my_func)

– juanpa.arrivillaga
Jan 19 at 0:24





@NewgateAce in other words, there is nothing magical about the decorator syntax. It is equivalent to def my_function(): ...; my_func = deco(my_func)

– juanpa.arrivillaga
Jan 19 at 0:24













@juanpa.arrivillaga i see now, f = deco(f) makes it clearer for me. thanks for your reply.

– Newgate Ace
Jan 19 at 0:30





@juanpa.arrivillaga i see now, f = deco(f) makes it clearer for me. thanks for your reply.

– Newgate Ace
Jan 19 at 0:30













@juanpa.arrivillaga what im about to say might be stupid, but when i print "salut" and "deco(salut)", they dont have the same reference ...

– Newgate Ace
Jan 19 at 0:46





@juanpa.arrivillaga what im about to say might be stupid, but when i print "salut" and "deco(salut)", they dont have the same reference ...

– Newgate Ace
Jan 19 at 0:46



-

Popular posts from this blog

Homophylophilia

Image
Haec pagina ad tempus protecta est ob maleficia perpetua. Quaesemus, emendationes suggere in pagina disputationis vel magistratum ad hanc deprotegendam pete. Homophylophilia Hyacinthus complexus ab amante suo Apolline, in pictura Mors Hyacinthi quam Jean Broc pinxit. Homophylophilia est sui sexus vel generis amor vel mores romantici vel sexuales, res venerea masculina in masculos, aut mulier in mulieres appetentes. Hoc ingenium sexuale est "exemplar permanens vel inclinatio ad experiendam sexualem, adfectionalem, vel romanticam vim attrahendi," praecipue vel solum ex hominibus eiusdem sexús; notio "etiam ad hominis iudicium identitatis privatae socialisque in illis attractionibus conditum refert, in moribus quoque qui illos exprimant, et in societate communitatis aliorum qui illos communicent." [1] [2] Per aevos alii aliter rem definiverunt, sed Occidentali nostrae aetatis cultu civili non tantum ad ipsa acta erotica spectat, sed etiam igitur
Read more

Updating UILabel text programmatically using a function

Image
0 so I am trying to update the UIlabel text using a func. I have seen few other questions like mine and I tried their method but it doesn't work. fun returns no value when used in the UIlabel. I have shown my code below.It has to be noted that when I use the function in viewdidload I can retrieve the data. lazy var name: UILabel = { let lb = UILabel() lb.text? = getthename() lb.lineBreakMode = NSLineBreakMode.byWordWrapping lb.textColor = .mainGreen lb.textAlignment = .left lb.font = UIFont.boldSystemFont(ofSize:12.0) return lb }() func getthename() -> String { var wins : String = "" let ud = (Auth.auth().currentUser?.uid) self.ref = Database.database().reference() self.ref.child("Users").child(ud!).observeSingleEvent(of: .value, with: {(snapshot) in
Read more

Cloud Functions - OpenCV Videocapture Read method fails for larger files from cloud storage

Image
0 I created a cloud function to read a video file from cloud storage and read frames and create an image for each frame. This function works for small files which is 1-2 MB, However, this method fails while reading larger file 130 MB. import cv2 from google.cloud import storage vidcap = cv2.VideoCapture("https://storage.googleapis.com/[bucker_name]/[filename.mp4]") if vidcap.isOpened(): vidcap.open("https://storage.googleapis.com/[bucker_name]/[filename.mp4]") success,image = vidcap.read() print(success) Expected the print will return true and an image will hold an image of a first frame. python-3.x function opencv cloud share | improve this question
Read more