philiprehberger-type-guard

Runtime type checking decorators for function arguments.

Installation

pip install philiprehberger-type-guard

Usage

Basic Usage

from philiprehberger_type_guard import guard

@guard
def greet(name: str, times: int = 1) -> str:
    return name * times

greet("hello", 3)     # Works fine
greet(123, 3)          # Raises TypeGuardError

Generic Types

@guard
def process(items: list[int], lookup: dict[str, float]):
    ...

process([1, 2, 3], {"a": 1.0})  # OK
process(["a"], {})               # TypeGuardError

Union Types

@guard
def flexible(value: int | str | None):
    ...

flexible(42)     # OK
flexible("hi")   # OK
flexible(None)   # OK
flexible(3.14)   # TypeGuardError

Non-raising and assertion checks

For one-off checks outside the @guard decorator, use is_type() (boolean) or assert_type() (raises on mismatch).

from philiprehberger_type_guard import is_type, assert_type

is_type(5, int)              # True
is_type("x", int)            # False
is_type([1, 2], list[int])   # True
is_type(None, int | None)    # True

assert_type(5, int)                       # returns None
assert_type("x", int)                     # raises TypeGuardError
assert_type("x", int, name="user_id")     # custom name in message

assert_type() honors the global enable() / disable() toggle.

Global Toggle

from philiprehberger_type_guard import enable, disable

disable()  # Turn off all guards (e.g., in production)
enable()   # Turn back on

Error Details

from philiprehberger_type_guard import TypeGuardError

try:
    greet(123, 3)
except TypeGuardError as e:
    print(e.param)     # "name"
    print(e.expected)  # "str"
    print(e.actual)    # <class 'int'>
    print(e.value)     # 123

API

Development

pip install -e .
python -m pytest tests/ -v

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License

MIT