Function preconditions

components/dash-table/tests/selenium/conftest.py:25–98

(*precs)

def preconditions(*precs):
    stripped_source = lambda obj: inspect.getsource(obj).strip()

    if not precs:
        # This edge case makes ``@preconditions()`` efficiently delegate
        # to the wrapped function, which I anticipate will be useful
        # for stubbing and code consistency in applications:
        def null_decorator(f):
            f.nopre = f  # Meet the .nopre interface requirement.
            return f

        return null_decorator

    precinfo = []
    for p in precs:
        spec = inspect.getfullargspec(p)
        if spec.varargs or spec.varkw:
            raise PreconditionError(
                (
                    "Invalid precondition must not accept * nor ** args:\n" + "  {!s}\n"
                ).format(stripped_source(p))
            )

        i = -len(spec.defaults or ())
        if i == 0:
            appargs, closureargs = spec.args, []
        else:
            appargs, closureargs = spec.args[:i], spec.args[i:]
        precinfo.append((appargs, closureargs, p))

    def decorate(f):
        fspec = inspect.getfullargspec(f)

        for (appargs, closureargs, p) in precinfo:
            for apparg in appargs:
                if apparg not in fspec.args:
                    raise PreconditionError(
                        (
                            "Invalid precondition refers to unknown parameter {!r}:\n"
                            + "  {!s}\n"
                            + "Known parameters: {!r}\n"
                        ).format(apparg, stripped_source(p), fspec.args)
                    )
            for carg in closureargs:
                if carg in fspec.args:
                    raise PreconditionError(
                        (
                            "Invalid precondition masks parameter {!r}:\n"
                            + "  {!s}\n"
                            + "Known parameters: {!r}\n"
                        ).format(carg, stripped_source(p), fspec.args)
                    )

        @wraps(f)
        def g(*a, **kw):
            args = inspect.getcallargs(f, *a, **kw)
            for (appargs, _, p) in precinfo:
                if not p(*[args[aa] for aa in appargs]):