Issue 33452: add user notification that parent init will not be called in dataclass init method (original) (raw)

Issue33452

Created on 2018-05-09 20:50 by Ricyteach, last changed 2022-04-11 14:59 by admin.

Messages (3)
msg316331 - (view)	Author: Rick Teachey (Ricyteach) *	Date: 2018-05-09 20:50
The dataclasses module is incredibly easy to use. This is a good thing. BUT one downside is it will definitely be utilized by people who don't have a thorough understanding of how it does what it does. Even for me, despite having a very good understanding of how it works, after heavily using it on a project for about 3 weeks now I made a mistake like the one below: class ImportantMixin: def __init__(self): super().__init__() important_task() @dataclass class NaiveDClass(ImportantMixin): data1 = int data2 = int I then went on along my merry way. Obviously, ImportantMixin.__init__ never gets called and I didn't realize this until it was a bigger problem than it should have been (should have written better tests! but I digress). It would seem like a good idea for the dataclasses module to let the user know they did this, probably via the warning system. Seems like it would be relatively easy to do: if there is an init method being create, just inspect the MRO for any previously defined init methods that weren't created by dataclasses. Thanks.
msg316340 - (view)	Author: Eric V. Smith (eric.smith) *	Date: 2018-05-09 22:38
I'm okay with the concept, but I don't know how to implement it. You need to not only know if a class has a __init__, but also if it's expected to be called. For example, these don't normally get called, but if you inherit from them (and everyone does inherit from object) you don't want a warning. >>> hasattr(int, '__init__') True >>> hasattr(object, '__init__') True I'm open to ideas.
msg316343 - (view)	Author: Rick Teachey (Ricyteach) *	Date: 2018-05-10 02:27
The init method that comes up for int, str, float, etc is just the object init: assert int.__init__ is object.__init__ Probably the thing to do is grab any init methods that aren't the object.__init__ while stripping out the dataclass-created init methods? Maybe something like: import warnings if cls.__dataclass_params__.init: for pcls in cls.mro(): if pcls.__init__ is not object.__init__: try: d_params = getattr(pcls, "__dataclass_params__") except AttributeError: warnings.warn('Found a not called init') else: if not d_params.init: warnings.warn('Found a custom dataclass init')