Source code for hypothesis.extra.dpcontracts

# This file is part of Hypothesis, which may be found at
# Most of this work is copyright (C) 2013-2021 David R. MacIver
# (, but it contains contributions by others. See
# CONTRIBUTING.rst for a full list of people who may hold copyright, and
# consult the git log if you need to determine who owns an individual
# contribution.
# This Source Code Form is subject to the terms of the Mozilla Public License,
# v. 2.0. If a copy of the MPL was not distributed with this file, You can
# obtain one at


This module provides tools for working with the :pypi:`dpcontracts` library,
because `combining contracts and property-based testing works really well

It requires ``dpcontracts >= 0.4``.

from dpcontracts import PreconditionError

from hypothesis import reject
from hypothesis.errors import InvalidArgument
from hypothesis.internal.reflection import proxies

[docs]def fulfill(contract_func): """Decorate ``contract_func`` to reject calls which violate preconditions, and retry them with different arguments. This is a convenience function for testing internal code that uses :pypi:`dpcontracts`, to automatically filter out arguments that would be rejected by the public interface before triggering a contract error. This can be used as ``builds(fulfill(func), ...)`` or in the body of the test e.g. ``assert fulfill(func)(*args)``. """ if not hasattr(contract_func, "__contract_wrapped_func__"): raise InvalidArgument( f"{contract_func.__name__} has no dpcontracts preconditions" ) @proxies(contract_func) def inner(*args, **kwargs): try: return contract_func(*args, **kwargs) except PreconditionError: reject() return inner