FAQ: Object-Oriented Programming - Getters, Setters and Deleters

This community-built FAQ covers the “Getters, Setters and Deleters” exercise from the lesson “Object-Oriented Programming”.

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This exercise can be found in the following Codecademy content:

Learn Intermediate Python 3

FAQs on the exercise Getters, Setters and Deleters

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It’s very interesting, If we can remove an attribute after instantiating the class, can we establish any attribute of already existing class instance? So, means we can get different instances of the same class with different range of attributes, right?

Yes you’re quite right, for user-defined types we can add and remove many instance attributes at will. However, you’d normally want to use the same attributes (even if they aren’t the same value) on each instance so that all your instances shared a common interface. The alternative can get quite confusing.

Thank you for the answer! I understand that it’s not a good practice, but just to clear it up, how is it possible to add an instace attribute, not touching the whole class?

It’s possible because each instance is normally a new object so you’re binding new attributes to this object instead of to the class itself. If you meant how do you actually do it then a typical route is to just create an instance (a new object of that type) and use the dot notation and a simple assignment-

class Example:
    pass

instance_obj = Example()
instance_obj.attribute = 'test'

That’s how initialisation with the __init__ method works anyway, you’re just using self as a stand-in reference for the new instance object. The built-in setattr could be useful if the attribute needs to be set dynamically.

How it all works is more of an implementation detail (dictionaries in CPython). A lot of built-ins don’t allow for setting arbitrary attributes and you can do this yourself by overwriting __setattr__ to prevent new attributes being set (ignoring direct mutation of the dictionary) or as a side-effect of the __slots__ attribute (since there is no dictionary in that case).

Thank you very much!!