Setting common instance variables to all classes using decorator or metaclass

Question

I have a scenario where class A is initialized with parameters id,name,email,ticket. Then class B is initialized inside class A's method and the same parameters are required to be passed along and so on and so forth. Can these common attributes be set using a decorator or metaclass during class declaration.

class A:
  def __init__(self, id, name,  email, ticket):
       self.id = id
       self.name=name
       self.email=email
       self.ticket=ticket

  def __somefunc(self):
       # do something
        b = B(self.id, self.name, self.email, self.ticket)
        b.__dosomething()

Similarly...class C and so on.. I am finding it bit inappropriate sending all these repeated parameters to all the subsequent classes.

Maybe have A hold onto a dataclass and just pass that around? — user2201041
– user2201041, Commented Mar 6, 2019 at 19:49
Is there any further difference between A.__init__ and B.__init__? A class method B.from_A might also be appropriate, to encapsulate the process of creating an instance of B given an instance of A. — chepner
– chepner, Commented Mar 6, 2019 at 19:56
Can these common attributes be set using ...? set on the instance created in __somefunc only or on A also? — wwii
– wwii, Commented Mar 7, 2019 at 1:32
Why did you think of using a a decorator or meta class? You really haven't explained your motivation - what problem are you trying to solve? — wwii
– wwii, Commented Mar 7, 2019 at 14:28

wwii · Accepted Answer · 2019-03-07 14:26:42Z

2

If you are just trying to reduce the number of characters typed (appearing in the code), make a dictionary of those values and instantiate the other classes with it.

Class A:
  def __init__(self, id, name,  email, ticket):
       self.id = id
       self.name=name
       self.email=email
       self.ticket=ticket
       self.params = {'id':id, 'name':name,  'email':email, 'ticket':ticket} 

  def __somefunc(self):
       # do something
        b = B(**self.params)
        b.__dosomething()

Can these common attributes be set using a decorator or metaclass during class declaration.? Yes and probably.

edited Mar 7, 2019 at 14:26

answered Mar 6, 2019 at 19:50

wwii

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Comments

Yam Mesicka · Accepted Answer · 2019-03-06 20:31:49Z

1

You can use a class decorator to "remember" the parameters as part of the instance, so you would be able to access them using self.args and self.kwargs:

import functools


def remember_params(cls):
    @functools.wraps(cls)
    def instance_creator(*args, **kwargs):
        obj = cls(*args, **kwargs)
        obj.args = args
        obj.kwargs = kwargs
        return obj
    return instance_creator


class B:
    def __init__(*args, **kwargs):
        print(args, kwargs)


@remember_params
class C:
    def __init__(self, id, name, email, ticket):
        self.id = id
        self.name = name
        self.email = email
        self.ticket = ticket

    def something(self):
        b = B(*self.args, **self.kwargs)

edited Mar 6, 2019 at 20:31

answered Mar 6, 2019 at 19:51

Yam Mesicka

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