dataclasses: subclassing a dataclass without its fields inherited as init-fields #122920
Description
Feature or enhancement
Proposal:
I was wondering if it would be possible to allow subclassing a dataclass without automatically including its fields in Subclass.__init__ (in some sense, hiding the inherited fields).
When subclassing the dataclass AB below to create CD, the fields of AB become fields of CD, automatically included in __init__, __repr__, and other methods of CD.
@dataclass
class AB:
a: str
b: str
@dataclass
class CD(AB):
c: str
d: str
# CD is instantiated as `CD(a, b, c, d)`.In some of my use cases, the values of a and b are determined by the values of c and d in instances of CD (in some sense, instances of CD are "fully determined" by c and d). Typically, I set those values in __post_init__. However, since a and b are automatically included in some methods, I hide them manually:
@dataclass
class AB:
a: str
b: str
def hidden_field(default=MISSING):
return field(default=default, init=False, repr=False, compare=False)
@dataclass
class CD(AB):
c: str
d: str
a = hidden_field("Hello World")
b = hidden_field()
def __post_init__(self):
self.b = c + d
# CD is instantiated as `CD(c, d)`,
# but behavior from `AB` using `a` and `b` is still available.I was wondering if, in the dataclass decorator for CD, an argument could be used to achieve this behavior, something like the following. I imagine this feature would be useful when a class like CD needs behavior from AB, but fields like a and b have predetermined values or values determined by fields of CD. One potential issue is that comparison (I believe) is broken between CD and AB instances.
@dataclass
class AB:
a: str
b: str
@dataclass(hide_inherited_fields=True)
class CD(AB):
c: str
d: str
def __post_init__(self):
self.a = "Hello World"
self.b = c + d
# CD is instantiated as `CD(c, d)`.Perhaps a specific set of fields could be ignored by the decorator argument, and the library could even include a function like hidden_field.
Thank you!
Has this already been discussed elsewhere?
This is a minor feature, which does not need previous discussion elsewhere
Links to previous discussion of this feature:
No response