Presenting “izulu”

Bring OOP into exception/error management

You can read docs from top to bottom or jump straight into “Quickstart” section. For details note “Specifications” sections below.

Neat #1: Stop messing with raw strings and manual message formatting

if not data:
    raise ValueError("Data is invalid: no data")

amount = data["amount"]
if amount < 0:
    raise ValueError(f"Data is invalid: amount can't be negative ({amount})")
elif amount > 1000:
    raise ValueError(f"Data is invalid: amount is too large ({amount})")

if data["status"] not in {"READY", "IN_PROGRESS"}:
    raise ValueError("Data is invalid: unprocessable status")

With izulu you can forget about manual error message management all over the codebase!

class ValidationError(Error):
    __template__ = "Data is invalid: {reason}"
    reason: str

class AmountValidationError(ValidationError):
    __template__ = "Invalid amount: {amount}"
    amount: int


if not data:
    raise ValidationError(reason="no data")

amount = data["amount"]
if amount < 0:
    raise AmountValidationError(reason="amount can't be negative", amount=amount)
elif amount > 1000:
    raise AmountValidationError(reason="amount is too large", amount=amount)

if data["status"] not in {"READY", "IN_PROGRESS"}:
    raise ValidationError(reason="unprocessable status")

Provide only variable data for error instantiations. Keep static data within error class.

Under the hood kwargs are used to format __template__ into final error message.

Neat #2: Attribute errors with useful fields

from falcon import HTTPBadRequest

class AmountValidationError(ValidationError):
    __template__ = "Data is invalid: {reason} ({amount})"
    reason: str
    amount: int


try:
    validate(data)
except AmountValidationError as e:
    if e.amount < 0:
        raise HTTPBadRequest(f"Bad amount: {e.amount}")
    raise

Annotated instance attributes automatically populated from kwargs.

Neat #3: Static and dynamic defaults

class AmountValidationError(ValidationError):
    __template__ = "Data is invalid: {reason} ({amount}; MAX={_MAX}) at {ts}"
    _MAX: ClassVar[int] = 1000
    amount: int
    reason: str = "amount is too large"
    ts: datetime = factory(datetime.now)


print(AmountValidationError(amount=15000))
# Data is invalid: amount is too large (15000; MAX=1000) at 2024-01-13 22:59:25.132699

print(AmountValidationError(amount=-1, reason="amount can't be negative"))
# Data is invalid: amount can't be negative (-1; MAX=1000) at 2024-01-13 22:59:54.482577