On Mon, May 2, 2022 at 9:30 PM Joao S. O. Bueno <jsbueno@python.org.br> wrote:
Anyway, there is something dataclasses do today that prevent you from jsut adding a @dataclass for binding __init__ attributes from an otherwise "complete class that does things":
I nor anyone else ever claimed dataclasses could be used for everything. You are quite right that you can’t make a dataclass that subclasses a non-dataclass— particularly when the subclass takes fewer parameters in its __init__. But that’s a bit of an anti-pattern anyway. In [17]: from dataclasses import dataclass
In [18]:
In [18]: @dataclass ...: class A: ...: a: int ...: def __post_init__(self, **kwargs): ...: print(kwargs) ...:
In [19]: A(1, b=3) --------------------------------------------------------------------------- TypeError Traceback (most recent call last) Input In [19], in <cell line: 1>() ----> 1 A(1, b=3)
TypeError: A.__init__() got an unexpected keyword argument 'b'
Why would you not write that as: @dataclass class A: a: int b: int def __post_init__(self, **kwargs): print(kwargs) If you really don't want b, you could remove it in the __post_init__ -- but as stated earlier in this thread, dataclasses are not a good idea if you have to do a lot of hand-manipulation -- you might as well write a standard class. And if you are subclassing, and need to have a parameter passed on to the superclass, you need to deal with that by hand anyway: class A(B): def __init__(self, a): super.__init__(a, b) is clearly not going to work, so you do: class A(B): def __init__(self, a, b): super.__init__(a, b) unless you do: class A(B): def __init__(self, a, *args, **kwags): super.__init__(a, *args, **kwargs) which is indeed a common pattern, and not supported by datclasses *yet -- there's talk of adding a way to support **kwargs. The problem with toy examples is that we can have no idea how best to solve a non-problem -- so we have no idea if the point being made is valid -- it's a challenge. But yes, there are many use cases not suited to dataclasses. The question is how many of these would rap parge benefit from auto-assigning syntax? I re-iterate that while I'd find this an useful addition,
I agree.
I think new syntax for this would be overkill.
And I agree there, too. -CHB