Despite the whole point of built-in dataclasses is to prevent boilerplate code - counter-intuitively, this is exactly what they lead to if you try to write clean, pythonic and - especially - type-hinted code.

To avoid heavy dependencies, I kept reimplementing basically the same stuff for dataclasses in many of my python projects, until I got sick of it. So, here's this package. I made it just for myself (to share the heavily reused code between the projects), but feel free to use it.

Type-hints

Defines:

• _P_Dataclass as dataclass protocol;
• _T_Dataclass as its respective (bound) TypeVar;
• _T as a bonus (just an arbitrary TypeVar).

They're deliberately named as protected members (start with _), but still imported with:

from darlog.dataclass import *

Conditional kwargs

dataclass decorator has different sets of arguments for various python versions. Infamously, slots was added only in 3.10. The following static classes behave like dicts that specify (or not) a specific argument, depending on the current version of python interpreter.

Usage is simple: just pass them as unpacked kwargs:

from darlog.dataclass import *

@dataclass(frozen=True, **Slots)
class DataClassWithSlotsWhenPossible: ...

@dataclass(**Slots, **WeakrefSlot)
class DataClassWithWeakrefSlotsWhenPossible: ...

The metaclass they're made with - _OptionalKwargsMeta - is also available to make your own python-version-dependent kwargs. But it's imported only explicitly:

from darlog.dataclass import _OptionalKwargsMeta

class FrozenOnlySince39(metaclass=_OptionalKwargsMeta):
    kwargs = dict(frozen=True)
    min_python = (3, 9)

@dataclass(**FrozenOnlySince39)
class MyDataClass: ...

Utility functions

• dc_fields_dict: Return all the field names/values from the dataclass instance - as dict. No deep-copy.
• dc_override: Copy a dataclass instance to a new one, with optional overrides.

Base classes to inherit from

The following ABC classes define class-level methods:

• FieldAccessPropsDC - adds:
  • fields - tuple of Field,
  • field_names - tuple of str,
  • field_names_set - frozenset of str.
• UnsafeInitDC - adds unsafe_init, which silently swallows any invalid keyword arguments and creates the instance anyway (as long as required arguments passed).