Classes that only extend Device aren't treated as BlueskyDevices

If a plan accepts a parameter that is typed as a class that extends only Device but not any of the bluesky protocols, it is not recognised as a bluesky device and doesn't have the reference type added that supports passing devices by name.

from ophyd_async.core import Device

class Demo(Device):
    pass

def sample_plan(demo: Demo) -> MsgGenerator:
    yield from []

When trying to run this plan using a string name as the argument for demo, the error returned will be of the form Input should be an instance of Demo instead of the expected Value error, Device demo is not of type sample_plans.Demo.

I think this is down to a difference in how Protocols work compared to classes in the isinstance test.

>>> from typing import Protocol, runtime_checkable
...
... @runtime_checkable
... class Proto(Protocol):
...     def proto_method(self):...
...
... class Base:
...     pass
...
... class Foo(Proto):
...     pass
...
... class Bar(Base):
...     pass
...
>>> isinstance(Foo, Proto)
True
>>> isinstance(Bar, Base)
False

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Classes that only extend `Device` aren't treated as BlueskyDevices #1369

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Classes that only extend Device aren't treated as BlueskyDevices #1369

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tpoliaw commented on Jan 30, 2026

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Classes that only extend `Device` aren't treated as BlueskyDevices #1369