can you make a regular python class frozen?

Question

It's useful to be able to create frozen dataclasses. I'm wondering if there is a way to do something similar for regular python classes (ones with an __init__ function with complex logic possibly). It would be good to prevent modification after construction in some kind of elegant way, like frozen dataclasses.

Answer 1

yes.

All attribute access in Python is highly customizable, and this is just a feature dataclasses make use of.

The easiest way to control attribute setting is to create a custom __setattr__ method in your class - if you want to be able to create attributes during __init__ one of the ways is to have an specific parameter to control whether each instance is frozen already, and freeze it at the end of __init__:

class MyFrozen:
   _frozen = False
   def __init__(self, ...):
       ...
       self._frozen = True

   def __setattr__(self, attr, value):
       if getattr(self, "_frozen", None):
            raise AttributeError("Trying to set attribute on a frozen instance")
       return super().__setattr__(attr, value)