Get value from sync callback to coroutine few times

Question

I am working now around library for creating testing infrastructure for dbus objects via python-dbus-next library and i have a stuck around assertes for dbus property, which can changed via signal. Typical example of property update its simple sync callback on needed signal:

    ...interface initialisation....

    def _prop_change(prop: dict):
        print(f'Property changed dict')

    interface.on_property_changed(_prop_change)

In my case i want have watched property with expected value with until expression like next signature:

iface = await IFaceClient(bus_name, path, interface)
await iface.call_method('bla')
await iface.wait_property('bla_property').equal(30)

For this implementation i try use subscribe/unsubscribe callback handler with awaitable object from sync callbakc to asserter by Event object, but i see that my assert equal dont see that value been changed and try compare with initial value (None):

# handler on interface
    def wait_property(self, prop_name):
        event = asyncio.Event()
        value = None
        
        def property_changed(prop):
            nonlocal value
            nonlocal event
            value = prop.get(prop_name)

        self._iface.on_property_changed(property_changed)
        return Comparer(event, value)

Comparer object

class Comparer:

    timeout = 10

    def __init__(self, event, value):
        self.event = event
        self.value = value

    def until(self, t):
        self.timeout = t
        return self

    async def _eq(self, expected):
        f = asyncio.get_event_loop().create_future()
        try:
            await self.event.wait()
            assert self.value == expected
            f.set_result(self.value)
        except AssertionError:
            self.event.clear()
        return await f

    async def equal(self, value):
        try:
            return await asyncio.wait_for(self._eq(value), timeout=self.timeout)
        except asyncio.TimeoutError:
            raise AssertionError(f'Values isn`t equal: {self.value} != {value}')

In live loog i see that method_eq only once be called and check, but its get first value (none) I am also try use property value in call back but loking that corotine method doesnt see that value was changed and i get similar value (None).

I think about using Future object like container for value from call back, but it cant be implemented, cause working only once and not possible coverage case, when you wait assert property from transitiend state: property.equal(30) -> but property can start from 10, then 20, then 30 So, the question is - what i am doing wrong?

Get value from sync callback to coroutine few times

0 Answers0