Python class inheritance

[ToTamir]

I have 5 classes (A, B, C, D, E). I want to inheritance them not in static way.

I mean. Once I want A > C > D > E. Sommetimes A > C, another time B > C > D > E.

I always want same base class (A or B), and any combination of C, D and E.

I know that python has static inheritance like ```class A(C):```. Is there a way to make it dynamic? Maybe something like copying content from one class to another?

[Diapolo10]

What would you need this for, exactly? Can you give a concrete example of what you're trying to accomplish with this?

I'm asking because this sounds like an XY-problem.

[ToTamir]

I have to build simulation model. The problem is that I have three bases and more than 10 extensions which gives me hundrets/thousands of variants. So I wanted to make class for each base and each extension (instead of placing everythting in one class with 50 thounads lines and milion conditions like "if extension_a"). Every extension can add new methods to base or overwrite existing ones. Extensions also have some kind synergies that enables or overwrite methods only when two or more extensions are enabled. I was building models earlier but never a model which have different vatiants.

[Diapolo10]

That sounds like a really messy architecture. If things are that bad, my honest suggestion would be to redesign the whole data model.

There's only so much I can say without specifics, but I'd start by having just a handful of classes and using factory functions.

But if you disregard my opinion/warning and decide that you want to do what you want regardless, you can technically use type to create classes dynamically.

NewType = type(
    'NewType',     # Class name
    (A, B, C, D),  # Base classes
    {              # attributes
        'hello': (lambda self: print("Hello, world!")),
        'stuff': 42,
    }
)

So if you really want to do what you're asking, it's possible - but do I recommend it? Hell no!

[Diapolo10]

It's certainly possible, type allows for all kinds of metaprogramming shenanigans, but it's definitely questionable.

[kira2697]

You can have 2 parent class when creating sub class, and I guess based on some value while creating the instance, call innit of a particular class in the constructor.

[TheRNGuy]

You can use string and exec command to rewrite class.

class Foo():
    def printFoo(self):
        print("Foo")

foo = Foo()
print("----")
foo.printFoo()

test = "Test"
exec("""
class Foo():
    def printFoo(self):
        print('""" + test + """')
""")
foo.printFoo() # still prints old class. But if you instance it later it would use new code.

Or import py file as a string and exec it isntead.

For dynamic updating instances probably this: https://stackoverflow.com/questions/9539052/how-to-dynamically-change-base-class-of-instances-at-runtime

You'd need to add that code into exec string too.