@classmethod question

[Scott SA]

Hi,

I'm using the @classemethod decorator for some convenience methods and for some reason, either mental block or otherwise, can't seem to figure out how to elegantly detect if the call is from an instance or not.

Here's the problem: Within the class definition, 'isinstance' has nothing to compare to because the class does not appear to exist.

This is NOT a great example, but it outlines the the code:

    class RecipieClass:
        def __init__(self):
            pass
        
        @classmethod
        def get_ingrendients(self, recipie_list=None):
            
            if isinstnace(self,RecipieClass):
                return self.do_something_interesting()
            else:
                return do_something_boring(recipie_list)

Yes, I can test to see if the param exists, but that makes the call exclusive i.e. I can _only_ call it as an instance or with a parameter.

Why am I doing this?

It is a series of convenience methods, in this case I'm interacting with a database via an ORM (object-relational model). I want the ability to call a class-ojbect and get related values, or pass some criteria and get related values for them without collecting the records first as instances, then iterating them. I need to call this from several places so I want to be DRY (don't repeat yourself).

The easiest way to describe this as an analogy would be like having a recipie for cookies and wanting to know all of the ingredients ahead of time. Then, at another time, wanting to know what all the ingredients would be to make cookies, cake and bread (i.e. complete shopping list).
    
  cookie_recipie = RecipieClass.get_recipie('cookies')
  cookie_recipie.get_ingredients()
        2C Flour
        0.5 C Sugar
        ...
        
  RecipieClass.get_ingrendients(['cookies','cake','bread'])
        8C Flour
        2C Sugar
        ...

Of course any suggestions on how this might be better approached would be interesting too.

TIA,

Scott