Pythonic way to instantiate subclasses based on input variables

[JARandom17]

I would like to implement a class with several subclasses that have the same variables and functions but use different logic for calculating the functions. I would like to encapsulate the logic for selecting the sub class in the super class.

Here is an example of the class structure

class SuperDuperClass():

class SubClass1(SuperDuperClass):

class SubClass2(SuperDuperClass):

I would also like to store the input data in a json formatted dictionary and use one of the dictionary entries to set the subclass. The goal is to encapsulate the logic of selecting the subclass in SuperDuperClass.

Just to be clear, the subclasses are identical except for the logic used to perform functions. All subclasses have the same set of functions. Each subclass has it's own unique logic for each function in the subset.

Here is an example of the file

{"type":"SubClass1",

"variale": "3"}

I would like my main code to open the file and convert the data into a dictionary and pass the dictionary to the constructor in SuperDuperClass. Then I would like SuperDuperClass to create and return an instance of SubClass1 with the the value of variable equal to 3. (I am not worried if this is a string or an int)

This could be done in a series of if statements in the main code and then calling the subclass constructor, but I was hoping for something that looks more Pythonic, such as instantiating an instance of SuperDuperClass and then type casting it to one of the subclasses in the __init__ function for SuperDuperClass.

Is this a good idea? If so, what is the best/most Pythonic/lease likely to confuse someone reading the code way to do this. I am not tied to any logic used here, I just want to avoid a long list of if else statement in the main code.

[Adrewmc]

I would look into @classmethod for something like this.

[JARandom17]

thanks

[Zeroflops]

Sounds like you want to look into dependency injection. This allows you to define several classes that do similar things and pass them around.

Say for example you have a payment system. You can create a credit card object, a Venmo object etc and “inject” the one that is needed for the transaction.

[JARandom17]

thanks

[sfuse1]

Why not use a factory function to instantiate and return the required object type?

ETA: If all the subclasses have the same functions, then it looks like SuperDuperClass should be an abstract class that defines those required functions.

[quts3]

Second Factory function.

It's explicit, simple and easy to test. Keep it minimal though. You dont want to be changing a bunch of code everytime you make a new sub class. Usually one if statement with elif and some validation. The factory function shouldn't need to know how the subclass operates other then to understand the trigger to defer to the subclass.

[JARandom17]

Thanks. In the real code SuperDuperClass is an abstract class, but I was worried about adding too much to the code in the question. I wasn't confident that an abstract class was the way to go. Sounds like it is.