pythonpython-attrs

Using attrs is it ok to set init=False to an attribute with no default value

I use attrs library.

I use some attributes that are set by the __attrs_post_init__ method.

For them, I want to prevent them from being part of the constructor.

Is it ok to not put a default value, or is it an implicit requirement of putting init=False?

The doc is not really clear about it.

import attrs

@attrs.define
class MyClass:
    val1: str = attrs.field(init=False)
    def __attrs_post_init__(self):
        self.val1="something"

a = MyClass()
print(a)

a.val1

This code is working, however I wonder if it’s relevant regarding the best practices.

Solution

  • That's perfectly fine. With init=False you're opting out of attrs's __init__.

    You can always try import inspect; inspect.getsource(MyClass.__init__) if you're curious what's happening under the hood.