simple-type-checker 2.1.1

A small extendable python type checker library

simple_type_checker

A small extendable python type checker library

Basic Usage

Checking a type:

from simple_type_checker import type_check
assert type_check("A string", str)

As a decorator:

from simple_type_checker import type_check, TypeCheckFailed

@type_check.returns
def id_(x) -> int:
    return x

_ = id_(1)  # Passes
try:
    id_("string")
except TypeCheckFailed as e:
    print("Bad input: ", e)

Decorators for aruments exist as well: type_check.args. Both can be done at once with type_check.decorate.

With custom types

Basic types where isinstance is sufficient:

from simple_type_checker import TypeChecker

class Foo:
    pass

type_check = TypeChecker(Foo)

assert type_check(Foo(), Foo)

Special type checking logic desired

from simple_type_checker import TypeChecker, Checker

class Bar:
    def __init__(self, b):
        self.can_check = b

class CheckerBar(Checker):
    def __call__(self, obj: Any, type_: Any) -> bool:
        return type_ == Bar and isinstance(obj, Bar) and obj.can_check

type_check = TypeChecker(advanced=(Bar,))

assert type_check(Bad(True), Bar)
assert not type_check(Bad(False), Bar)

This use case is useful for container types that take arguments, for example.

Failures

This will may work with quoted type annotations without adding a custom type Checker. For example, the following will fail:

from simple_type_checker import type_check
Bar = list[int | "Bar"]

@type_check.returns
def f() -> Bar:
    return []

This is because no type checker knows what "MyType" is. Fixing this is as easy as adding a custom Checker that accepts "MyType" as a valid type, as demonstrated with CheckerBar above.