Using setattr in python

Question

I am looking for someone to explain the basics of how to use  and not use setattr     My problem arose trying to use one class method function to return data that is then put in another method function  Perhaps a simpler approach would be much better in this case  but I m trying to understand how classes work are used  This problem seems to hinge on setattr    and this is my attempt to make a fairly simple use of this       Though it s not quite the same problem  I was following Python The Hard Way  ex42 mdash the while loop   lines 18-41   I tried writing an    init      and using getattr   instead  thinking perhaps something needed to be in the class  namespace  but this doesn t seem to help       bin python2 6  class HolyGrail object        def   init   self           self start    start at init         function definition in question        TypeError   str  object is not callable      def run it self           start   setattr self   name    get thing           start   self name            Something wrong here          value returned   start    I believe this    self get thing           use it value returned                 alternate function definitions       NameError  global name  start  is not defined      def   init   self           self start    get thing       def run it self           go do it   getattr self  start          first output   go do it           use it first output               def get thing self           return  The Knights Who Say     Ni        def use it self  x           print x         print  We want a shrubbery    my instance   HolyGrail   my instance run it        Karl Knechtel   Amber    Chris Morgan  thanks for your help   I think I can now explain my own answer  This required a better grasp of self as an object for me   It s an instance name that gets tagged up with stuff like attributes   The class could be a Town  and then  getattr looks for a house using it s name so you are ready to call on it soon  and comes up with a different place if you don t find the house --With getattr a  name  exists  and you go find it  Makes the step from one function to another dynamic As a bonus you may have a default value  useful to get a fallback default method--connection failed or something   setattr builds a house and gives it a name so you can call in on it later  You could potentially rebuild this house  or go to a particular place if you are unable to find it  --setattr makes an attribute name and gives  or changes it s value  to be called on later Perhaps a user turns sound off  then future methods don t output any audio   I could have written my function a number of ways  but there s no need to change any attributes   def run it self       yo   getattr self   get thing       answer   yo       setattr self   deal accepted   self use it   really ott     no   getattr self   deal accepted       no answer    Properly corrected code   def run it self       value returned   self get thing       self use it value returned

User · Answer

Setattr  We use setattr to add an attribute to our class instance  We pass the class instance  the attribute name  and the value  and with getattr we retrive these values  For example  Employee   type  Employee    object    dict     employee   Employee      Set salary to 1000 setattr employee  salary   1000      Get the Salary value   getattr employee   salary    print value

User · Answer

I m here in general only to find out that through dict it is necessary to work inside setattr XD

User · Answer

To add to the other answers  a common use case I have found for setattr   is when using configs  It is common to parse configs from a file   ini file or whatever  into a dictionary  So you end up with something like   configs     memory   2 5   colour    red    charge   0          If you want to then assign these configs to a class to be stored and passed around  you could do simple assignment   MyClass memory   configs  memory   MyClass colour   configs  colour   MyClass charge   configs  charge         However  it is much easier and less verbose to loop over the configs  and setattr   like so   for name  val in configs items        setattr MyClass  name  val    As long as your dictionary keys have the proper names  this works very well and is nice and tidy     Note  the dict keys need to be strings as they will be the class object names

User · Answer

Suppose you want to give attributes to an instance which was previously not written in code   The setattr   does just that   It takes the instance of the class self and key and value to set    class Example      def   init   self    kwargs           for key  value in kwargs items                setattr self  key  value

User · Answer

The Python docs say all that needs to be said  as far as I can see   setattr object  name  value  This is the counterpart of getattr    The arguments are an object  a string and an arbitrary value  The string may name an existing attribute or a new attribute  The function assigns the value to the attribute  provided the object allows it  For example  setattr x   foobar   123  is equivalent to x foobar   123   If this isn t enough  explain what you don t understand

User · Answer

You are setting self name to the string  get thing   not the function get thing   If you want self name to be a function  then you should set it to one   setattr self   name   self get thing    However  that s completely unnecessary for your other code  because you could just call it directly   value returned   self get thing

[python] Using setattr() in python

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