README.md

Type-based validators for attrs classes

Typically, when you define an attrs class, you'll specify a type annotation for communicating types to human readers and automated type checkers. But then you'll also duplicate the type information in a validator to ensure that the code will perform runtime type checks. To avoid that duplication, you have two options. You can use this module as stand-in for attrs like so:

import attrhelpers as attr

@attr.s(auto_attribs=True, frozen=True)
class X:
    a: Optional[int]
    b: Sequence[float]
    c: str = attr.ib(default='hi')

Or you can use a lower level approach and import the type_validate decorator from this module. Use it before attr.s; it will create attrs validators based on the type annotations you supply. For example, this:

import attr
from attrhelpers import type_validate

@attr.s(frozen=True)
@type_validate
class X:
    a: Optional[int] = attr.ib()
    b: Sequence[float] = attr.ib()
    c: str = attr.ib(default='hi')

Both code snippets above are equivalent to:

@attr.s(frozen=True)
class X:
    a: Optional[int] = attr.ib(validator=optional(instance_of(int)))
    b: Sequence[float] = attr.ib(validator=deep_iterable(
        instance_of(float),
        instance_of(collections.abc.Sequence)))
    c: str = attr.ib(default='hi', valiator=instance_of(str))

Note that type_validate WILL NOT WORK with attr.s(auto_attribs); you must use attr.ib for each attribute in the class body.