Class method decorator with self arguments

Question

How do I pass a class field to a decorator on a class method as an argument   What I want to do is something like   class Client object       def   init   self  url           self url   url       check authorization  some attr   self url      def get self           do work     It complains that self does not exist for passing self url to the decorator   Is there a way around this

User · Accepted Answer

Yes  Instead of passing in the instance attribute at class definition time  check it at runtime   def check authorization f       def wrapper  args           print args 0  url         return f  args      return wrapper  class Client object       def   init   self  url           self url   url       check authorization     def get self           print  get    gt  gt  gt  Client  http   www google com   get   http   www google com get   The decorator intercepts the method arguments  the first argument is the instance  so it reads the attribute off of that  You can pass in the attribute name as a string to the decorator and use getattr if you don t want to hardcode the attribute name   def check authorization attribute       def  check authorization f           def wrapper self   args               print getattr self  attribute              return f self   args          return wrapper     return  check authorization

User · Answer

I know this is an old question  but this solution has not been mentioned yet  hopefully it may help someone even today  after 8 years  So  what about wrapping a wrapper  Let s assume one cannot change the decorator neither decorate those methods in init  they may be  property decorated or whatever   There is always a possibility to create custom  class-specific decorator that will capture self and subsequently call the original decorator  passing runtime attribute to it  Here is a working example  f-strings require python 3 6   import functools    imagine this is at some different place and cannot be changed def check authorization some attr  url           def decorator func                    functools wraps func                  def wrapper  args    kwargs                           print f quot checking authorization for   url      quot                           return func  args    kwargs                  return wrapper         return decorator    another dummy function to make the example work def do work            print  quot work is done    quot                          wrapped wrapper                       def custom check authorization some attr           def decorator func                     assuming this will be used only on this particular class                  functools wraps func                  def wrapper self   args    kwargs                             get url                         url   self url                           decorate function with original decorator  pass url                         return check authorization some attr  url  func  self   args    kwargs                  return wrapper         return decorator                                          original example  updated                                 class Client object           def   init   self  url                   self url   url               custom check authorization  quot some attr quot           def get self                   do work      create object client   Client r quot https   stackoverflow com questions 11731136 class-method-decorator-with-self-arguments quot      call decorated function client get    output  checking authorisation for  https   stackoverflow com questions 11731136 class-method-decorator-with-self-arguments     work is done

User · Answer

from re import search from functools import wraps  def is match  lambda  pattern       def wrapper f            wraps f          def wrapped self   f args    f kwargs               if callable  lambda  and search pattern    lambda self  or                        f self   f args    f kwargs          return wrapped     return wrapper  class MyTest object        def   init   self           self name    foo          self surname    bar        is match lambda x  x name   foo        is match lambda x  x surname   foo       def my rule self           print  my rule   ok        is match lambda x  x name   foo        is match lambda x  x surname   bar       def my rule2 self           print  my rule2   ok     test   MyTest   test my rule   test my rule2        ouput    my rule2   ok

User · Answer

Another option would be to abandon the syntactic sugar and decorate in the   init   of the class  def countdown number       def countdown decorator func           def func wrapper                for index in reversed range 1  number 1                    print index              func           return func wrapper     return countdown decorator  class MySuperClass        def   init   self  number           self number   number         self do thing   countdown number  self do thing           def do thing self           print  im doing stuff      myclass   MySuperClass 3   myclass do thing    which would print 3 2 1 im doing stuff

User · Answer

You can t  There s no self in the class body  because no instance exists  You d need to pass it  say  a str containing the attribute name to lookup on the instance  which the returned function can then do  or use a different method entirely

User · Answer

A more concise example might be as follows     usr bin env python3 from functools import wraps  def wrapper method        wraps method      def  impl self   method args    method kwargs           method output   method self   method args    method kwargs          return method output           return  impl  class Foo       wrapper     def bar self  word           return word  f   Foo   result   f bar  kitty   print result    Which will print   kitty

[python] Class method decorator with self arguments?

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