CODEWITHSUNDEEP
pythonimportmodule
user2032433
user2032433

Reputation:

Global imports in inheritance?

Imagine a module called base with a class called Base in it. Now inside an other module, called sub, inherit a class Sub from Base:

import base
class Sub(base.Base):
    pass

Now what if we add a third class, that inherits from Sub and takes a parameter that has to be type of Base or one of it's subclasses:

import sub
class Deep(sub.Sub):
    def __init__(self, parent):
        if isinstance(parent, sub.base.Base):
            pass

Going deeper and deeper down in the inheritance tree, the path to Base will become thedeepest.deeperanddeeper.reallydeep.deep.sub.base.Base, which nobody would like.

I could of course just do from base import * and from sub import * and then just use Base, but is there a way to import so that I can use the prefix of ONLY the original module of my class?

For example:

import deep
class ReallyDeep(deep.Deep):
    def __init__(self, parent):
        # I know my polymorphism, this is just an example.
        if isinstance(parent, sub.Sub):
            pass
        elif isinstance(parent, base.Base):
            pass

Upvotes: 0

Views: 138

Answers (1)

Blubber
Blubber

Reputation: 2254

Modules in Python are like singletons, they only get imported once, so

import base
import deep
class ReallyDeep(deep.Deep):
    def __init__(self, parent):
       if isinstance(parent, base.Base):
           pass

Is absolutely no problem at all, in fact, it's the best way to do it.

What delnan means is that in most cases deeply nested inheritance trees are a sign of bad design. As with any rule, there are exceptions. But in general avoiding deeply nested trees will make your code more understandable, easier to test and therefore easier to maintain.

Upvotes: 1

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