prerequisites

Small runtime validation helpers for preconditions and type checks.

Install

pip install prerequisites

What it provides

• Value checks: require, require_one_in_all, require_all_in_all
• Type checks: require_type, require_one_of_types, require_all_of_type, require_all_same_type, require_type_or_none
• Decorator checks: @validate_types for argument validation using type hints

Quick examples

Value checks

from prerequisites import require, require_all_in_all, require_one_in_all

require(2 > 1)
require_one_in_all([False, True, False])
require_all_in_all([True, 2 + 2 == 4])

Type checks

from prerequisites import (
    require_all_of_type,
    require_all_same_type,
    require_one_of_types,
    require_type,
    require_type_or_none,
)

require_type(10, int)
require_one_of_types(3.14, (int, float))
require_all_of_type([1, 2, 3], int)
require_all_same_type(["a", "b", "c"], (str,))
require_type_or_none(None, str)

Decorator validation

from prerequisites import validate_types

@validate_types
def add(a: int, b: int) -> int:
    return a + b

add(1, 2)      # ok
add("1", 2)   # raises TypeError

Shallow container behavior

@validate_types validates only outer container types for parameterized hints.

from prerequisites import validate_types

@validate_types
def count(values: list[int]) -> int:
    return len(values)

count([1, 2, 3])
count([1, "x"])  # valid in current shallow mode (still a list)

Notes

• @validate_types validates function arguments only.
• Return annotations are not enforced.
• Errors raise TypeError or ValueError depending on the helper.