Overview
Lodum provides a set of validator classes for runtime validation of deserialized values. All validators inherit from the base Validator class and raise DeserializationError when validation fails.
Validator Base Class
The abstract base class for all validators.
from lodum.validators import Validator
class Validator:
def __call__(self, value: Any) -> None:
raise NotImplementedError
Range
Validates that a value falls within a specified numeric range.
from lodum.validators import Range
Constructor
min
Optional[Any]
default:"None"
Minimum acceptable value (inclusive). If None, no minimum is enforced.
max
Optional[Any]
default:"None"
Maximum acceptable value (inclusive). If None, no maximum is enforced.
Behavior
Raises DeserializationError if:
- Value is less than
min (when min is not None)
- Value is greater than
max (when max is not None)
Example
from lodum import lodum, field
from lodum.validators import Range
@lodum
class Product:
price: float = field(validate=[Range(min=0.0, max=10000.0)])
quantity: int = field(validate=[Range(min=1)])
# Valid
product = Product(price=99.99, quantity=5)
# Raises DeserializationError: "Value -10 is less than minimum 0.0"
product = Product(price=-10, quantity=5)
# Raises DeserializationError: "Value 15000 is greater than maximum 10000.0"
product = Product(price=15000, quantity=5)
Length
Validates the length of sequences, strings, or any object supporting len().
from lodum.validators import Length
Constructor
min
Optional[int]
default:"None"
Minimum acceptable length (inclusive). If None, no minimum is enforced.
max
Optional[int]
default:"None"
Maximum acceptable length (inclusive). If None, no maximum is enforced.
Behavior
Raises DeserializationError if:
- The value does not support
len() operation
- Length is less than
min (when min is not None)
- Length is greater than
max (when max is not None)
Example
from lodum import lodum, field
from lodum.validators import Length
@lodum
class User:
username: str = field(validate=[Length(min=3, max=20)])
tags: list[str] = Field(validators=[Length(max=5)])
# Valid
user = User(username="alice", tags=["python", "coding"])
# Raises DeserializationError: "Length 2 is less than minimum 3"
user = User(username="ab", tags=[])
# Raises DeserializationError: "Length 6 is greater than maximum 5"
user = User(username="alice", tags=["a", "b", "c", "d", "e", "f"])
Match
Validates that a string value matches a regular expression pattern.
from lodum.validators import Match
Constructor
Regular expression pattern to match against. Uses Python’s re module.
Behavior
Raises DeserializationError if:
- Value is not a string
- Value does not match the compiled regex pattern
Example
from lodum import lodum, field
from lodum.validators import Match
@lodum
class Contact:
email: str = field(validate=[Match(r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$')])
phone: str = field(validate=[Match(r'^\d{3}-\d{3}-\d{4}$')])
# Valid
contact = Contact(email="[email protected]", phone="555-123-4567")
# Raises DeserializationError: "Value 'invalid-email' does not match pattern..."
contact = Contact(email="invalid-email", phone="555-123-4567")
# Raises DeserializationError: value is not a string
contact = Contact(email=12345, phone="555-123-4567")
OneOf
Validates that a value is one of a predefined set of acceptable values.
from lodum.validators import OneOf
Constructor
A container of acceptable values. Any type supporting the in operator (list, set, tuple, etc.) can be used.
Behavior
Raises DeserializationError if the value is not in the options container.
Example
from lodum import lodum, field
from lodum.validators import OneOf
@lodum
class Order:
status: str = field(validate=[OneOf(["pending", "processing", "shipped", "delivered"])])
priority: int = Field(validators=[OneOf({1, 2, 3})])
# Valid
order = Order(status="pending", priority=1)
# Raises DeserializationError: "Value 'cancelled' is not one of [...]"
order = Order(status="cancelled", priority=1)
# Raises DeserializationError: "Value 5 is not one of {1, 2, 3}"
order = Order(status="pending", priority=5)
Combining Validators
Multiple validators can be applied to a single field:
from lodum import lodum, field
from lodum.validators import Length, Match
@lodum
class Account:
password: str = field(validate=[
Length(min=8, max=128),
Match(r'^(?=.*[A-Z])(?=.*[a-z])(?=.*\d).*$') # Must contain uppercase, lowercase, and digit
])
DeserializationError.
Custom Validators
You can create custom validators by subclassing Validator:
from lodum import lodum, field
from lodum.validators import Validator
from lodum.exception import DeserializationError
class Even(Validator):
def __call__(self, value: int) -> None:
if value % 2 != 0:
raise DeserializationError(f"Value {value} is not even")
@lodum
class EvenNumber:
value: int = field(validate=[Even()])