A comparison of various ways of (declaratively) defining classes whose attributes comprise instance fields.

sample-a.py

from typeguard import typechecked


class Foo:
	@typechecked
	def __init__(self, name: str, age: int, gender: str = 'na'):
		self.name = name
		self.age = age
		self.gender = gender


print(Foo.__annotations__.get('name')) # -> None -- ugh, it's in the damn constructor.

sample-b.py

from dataclasses import dataclass


@dataclass
class Foo:
	name: str
	age: int
	gender: str = 'na'


print(Foo.__annotations__.get('name')) # -> str -- simple, yay! but… absolutely no way to specify behaviour.

sample-c.py

from marrow.schema import Container, Attribute


class Foo(Container):
	name = Attribute()
	age = Attribute()
	gender = Attribute(default='na')


print(Foo.__annotations__.get('name')) # -> None -- bugger, but sorta makes sense, these are generic "attributes"

sample-d.py

from marrow.mongo import Document
from marrow.mongo.field import String, Integer


class Foo(Document):
	name = String()
	age = Integer()
	gender = String(choices=('m', 'f', 'na'), default='na')


print(Foo.__annotations__.get('name')) # -> str -- works as of today

sample-e.py

# Imports **purely** for type annotation.  >_<

from typing import Union

from bson import ObjectId as OID
from collections.abc import MutableMapping
from datetime import datetime, timedelta

# Actual imports.

from marrow.mongo import Document
from marrow.mongo.field import ObjectId


class Foo(Document):
	id: Union[OID,datetime,timedelta,MutableMapping,str,bytes] = ObjectId()

# Imagine having to put that "boilerplate" everywhere you use an ObjectId field.
# Let me think long and no.