Corbel

Corbel is a Python dataclass extension library providing mixins and utilities for:

• Validation
• Comparison and hashing
• Copying and updating
• Serialization to/from dicts and JSON
• Property-level metadata (@corbel_property)
• Protocol-based hooks for validation, serialization, and deserialization

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Installation

pip install corbel

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Core Mixins

1. Corbel

The base mixin that provides:

• Cached asdict results
• Field and property introspection
• Hook methods for updates and validation

from corbel import dataclass
from corbel import Corbel, field

@dataclass
class Base(Corbel):
    x: int = field()
    y: str = field()

inst = Base(1, "hello")
print(inst.asdict())  # {'x': 1, 'y': 'hello'}

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2. Serializable

Provides to_dict, from_dict, to_json, from_json for dataclasses.

• Supports nested dataclasses
• Optional wrapper key for JSON (__json_wrapper__)
• Configurable inclusion rules (__inclusion__)

from corbel import dataclass
from corbel import Serializable, field, Include

@dataclass
class User(Serializable):
    id: int = field()
    name: str = field()
    email: str | None = field(default=None)

user = User(1, "Alice")
print(user.to_dict())  # {'id': 1, 'name': 'Alice', 'email': None}
alice = User.from_dict({"id": 1, "name": "Alice", "email": None})

# JSON with wrapper
print(user.to_json(wrapper="user"))  # {"user": {"id":1,"name":"Alice","email":null}}
alice = User.from_json('{"user": {"id":1,"name":"Alice","email":null}', wrapper="user")

# Custom class-level JSON wrapper
@dataclass
class WrappedUser(Serializable):
    __json_wrapper__ = "account"
    id: int = field()
    name: str = field()

u = WrappedUser(5, "Bob")
print(u.to_json())  # {"account": {"id":5,"name":"Bob"}}

# Using inclusion rules
@dataclass
class PartialUser(Serializable):
    __inclusion__ = Include.NON_NONE
    id: int = field()
    name: str = field()
    email: str | None = field(default=None)

pu = PartialUser(1, "Alice")
print(pu.to_dict())  # {'id': 1, 'name': 'Alice'}  # email omitted

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3. Updatable

Provides immutable-style updates:

• copy(): shallow copy
• update(**kwargs): returns a new instance with updated fields
• batch_update(): context manager to temporarily disable validation

from corbel import dataclass
from corbel import Updatable, field

@dataclass
class Point(Updatable):
    x: int = field()
    y: int = field()

p1 = Point(1, 2)
p2 = p1.update(x=10)  # new instance
print(p1.asdict())    # {'x': 1, 'y': 2}
print(p2.asdict())    # {'x': 10, 'y': 2}

# batch update
with p2.batch_update() as temp:
    temp.x = 20
    temp.y = 30
print(p2.asdict())  # {'x': 10, 'y': 2}, p2 unchanged

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4. Validated

Automatically validates fields on initialization and update:

• Define a validator in field() metadata
• Supports allow_none=True
• Raises ValidationError on failure

from corbel import dataclass
from corbel import Validated, field, ValidationError

def positive(value: int) -> bool:
    return value > 0

@dataclass
class BankAccount(Validated):
    balance: int = field(validator=positive)

try:
    acct = BankAccount(-10)  # raises ValidationError
except ValidationError as e:
    print(e)

acct = BankAccount(100)
acct.balance = -50  # raises ValidationError

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5. Hashable

Caches a hash based on dataclass fields:

• Automatically invalidates on field update
• Suitable for dict keys and set members

from corbel import dataclass
from corbel import Hashable, field

@dataclass
class Coord(Hashable):
    x: int = field()
    y: int = field()

c1 = Coord(1, 2)
c2 = Coord(1, 2)

print(hash(c1) == hash(c2))  # True
c1.x = 3
print(hash(c1) == hash(c2))  # False

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6. Comparable

Provides <, <=, >, >=, == based on field values:

• Lexicographic comparison of fields
• Supports total ordering

from corbel import dataclass
from corbel import Comparable, field

@dataclass
class Version(Comparable):
    major: int = field()
    minor: int = field()

v1 = Version(1, 0)
v2 = Version(1, 1)
print(v1 < v2)  # True
print(v1 == v2) # False

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7. @corbel_property

Custom property decorator supporting:

• validator
• serializer / deserializer
• allow_none / ignore

from corbel import dataclass
from corbel import Corbel, corbel_property, field

def positive(x: int) -> bool:
    return x > 0

@dataclass
class Example(Corbel):
    _value: int = field()

    @corbel_property(validator=lambda v: positive(v))
    def value(self) -> int:
        return self._value

    @value.setter
    def value(self, val: int) -> None:
        self._value = val

ex = Example(5)
print(ex.value)  # 5
ex.value = 10    # OK
# ex.value = -1  # Raises ValueError

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8. Protocol Examples

ValidatorProtocol

from typing import Any

def positive_validator(value: int) -> bool:
    return value > 0

print(positive_validator(5))   # True
print(positive_validator(-1))  # False

SerializerProtocol

from typing import Any

def uppercase_serializer(value: Any) -> Any:
    if isinstance(value, str):
        return value.upper()
    return value

print(uppercase_serializer("hello"))  # "HELLO"

DeserializerProtocol

from typing import Any

def deserialize_int(value: Any, type_hint: int) -> int:
    if type_hint == int and isinstance(value, str):
        return int(value)
    return value

print(deserialize_int("42", int))  # 42

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9. Combining Mixins

Mixins can be combined for full-featured dataclasses:

from corbel import dataclass
from corbel import Serializable, Updatable, Validated, Hashable, Comparable, field, corbel_property

@dataclass
class Product(Serializable, Updatable, Validated, Hashable, Comparable):
    name: str = field()
    price: float = field()

    @corbel_property()
    def discounted_price(self) -> float:
        return self.price * 0.9

prod = Product("Widget", 100)
prod2 = prod.update(price=120)
print(prod.to_dict())  # {'name': 'Widget', 'price': 100}
print(prod2.discounted_price)  # 108.0

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Utilities

• asdict(obj, include_private=False): convert instance to dict
• field(**kwargs): wrapper for dataclass fields with Corbel metadata
• fields(obj): returns dataclass fields
• Include enum: ALWAYS, NON_NONE, NON_EMPTY, NON_DEFAULT
• Exceptions: ValidationError, DeserializeError, InclusionError, CorbelError
• Class-level options for Serializable:
  • __json_wrapper__ – wrap the JSON output under a key
  • __inclusion__ – control which fields are included

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License

MIT License. See LICENSE.