Python: Dynamically Adding Attributes To A Built-in Class
Why doesn't it work for the built-in classes? Is using a subclass the best approach to fix it, or will I run into some hidden problems? a = {} a.p = 1 # raises AttributeError class
Solution 1:
The builtin classes do not have the ability to have arbitrary attributes. This is done for reasons of performance, especially memory usage, you want the built-in classes like list
and dict
to be as small as possible so you can have many of them.
Therefore the built-in classes do not have the __dict__
dictionary that is needed for arbitrary attributes to work.
You can achieve the same for your classes. If they are written in C you simply do not implement the __dict__
support. If they are written in Python you use slots.
Solution 2:
If you want to subclass dict
you can always use UserDict
(here the documentation).
And it works with what you're trying to do:
from collections import UserDict
a = UserDict()
a.p = 10# works fine
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