Class inheritance in Python 3.7 dataclasses

Question

I\'m currently trying my hands on the new dataclass constructions introduced in Python 3.7. I am currently stuck on trying to do some inheritance of a parent class. It looks

Answer 1

A possible work-around is to use monkey-patching to append the parent fields

import dataclasses as dc

def add_args(parent): 
    def decorator(orig):
        "Append parent's fields AFTER orig's fields"

        # Aggregate fields
        ff  = [(f.name, f.type, f) for f in dc.fields(dc.dataclass(orig))]
        ff += [(f.name, f.type, f) for f in dc.fields(dc.dataclass(parent))]

        new = dc.make_dataclass(orig.__name__, ff)
        new.__doc__ = orig.__doc__

        return new
    return decorator

class Animal:
    age: int = 0 

@add_args(Animal)
class Dog:
    name: str
    noise: str = "Woof!"

@add_args(Animal)
class Bird:
    name: str
    can_fly: bool = True

Dog("Dusty", 2)               # --> Dog(name='Dusty', noise=2, age=0)
b = Bird("Donald", False, 40) # --> Bird(name='Donald', can_fly=False, age=40)

It's also possible to prepend non-default fields, by checking if f.default is dc.MISSING, but this is probably too dirty.

While monkey-patching lacks some features of inheritance, it can still be used to add methods to all pseudo-child classes.

For more fine-grained control, set the default values using dc.field(compare=False, repr=True, ...)