Digesting function arguments into clear, reliable contracts.

Install it

conda install -c uibcdf argdigest

Use it

ArgDigest helps you normalize and validate input arguments at your API boundary, without forcing a single internal architecture.

from argdigest import arg_digest

@arg_digest(
    digestion_source="mylib._private.argdigest.argument",
    digestion_style="package",
    strictness="warn",
)
def get(molecular_system, selection="all", syntax="MolSysMT"):
    return molecular_system, selection, syntax

What happens here:

• ArgDigest resolves digesters for each argument and applies them before your logic runs.

• If an argument cannot be digested, behavior follows your strictness policy.

• Optional diagnostics can be emitted through SMonitor.

Two axes

That example covers one half of the problem: given an argument name, is its value valid and in canonical form? A library also needs the other half: may this function receive this argument at all, and does it have what it needs?

Axis	You declare
The function argument contract	a FunctionContract per function or family, and a Domain for functions taking **kwargs
The argument value contract	one digester per argument name

Without the first, a mistyped keyword is silently discarded, the call runs with the default, and you get back a plausible wrong answer. ArgDigest refuses it instead:

UnknownArgumentError: 'mylib.basic.get.get' does not accept the argument 'n_atomss'.
Did you mean 'n_atoms'?

A closed signature needs no declaration: it is held to its own parameters, because ArgDigest must never end up more permissive than Python, which already raises TypeError for an unexpected keyword. A function taking **kwargs opened its door on purpose, so it declares the domain those keywords come from:

# mylib/_private/argdigest/domain/attribute.py
from argdigest import Domain
from mylib.attribute import attributes, is_attribute

domain = Domain(name='attribute', contains=is_attribute,
                members=lambda: tuple(attributes))

# mylib/_private/argdigest/function/get.py
from argdigest import FunctionContract

contract = FunctionContract(caller='mylib.basic.get.get', admits='attribute')

Pointing the domain at your library’s own catalogue, rather than copying names into a list, is what keeps the two from drifting apart. describe_contract then renders the whole thing as data, which is how the real domain of a **kwargs function becomes readable — something inspect.signature cannot show.

Note

unknown_argument defaults to error from version 0.10.0. Set UNKNOWN_ARGUMENT = "warn" or "ignore" in your configuration module during a migration.