At the moment, Device naming happens via Device.set_name. This is called:

• in Device.__init__(name) at construction
• after construction by the init_devices or dodal.common.beamlines.beamline_utils.device_factory

This leads to some odd edge conditions:

class Base(Device):
    def __init__(self, name=""):
        self.signal1 = soft_signal_rw()
        super().__init__(name=name)

class Derived(Base):
    def __init__(self, name=""):
        super().__init__(name=name)
        self.signal2 = soft_signal_rw(name="blah")

# Naming at init only names those that are present when the superclass init is called
derived1 = Derived(name="derived")
assert derived1.signal1.name == "derived-signal1"
assert derived1.signal2.name == "blah"

# Naming after init names everything
derived2 = Derived()
derived2.set_name("derived")
assert derived2.signal1.name == "derived-signal1"
assert derived2.signal2.name == "derived-signal2"

This is inconsistent, so we should fix it.

Possible solutions:

1. Remove name from Device.__init__ and require Device.set_name to be called after creation
2. Set the name of child devices in Device.__setattr__

Both of those solutions will break one particular @rtuck99 had (that I can't remember details of) where set_name was never used after init, so the name "blah" in the above example was actually the desired name.

To support that use case we would have to override Derived.set_name to explicitly name signal2 to be "blah", either by overriding the baseclass set_name (for 1):

class Derived(Base):
    def set_name(self, name: str, *, child_name_separator: str | None = None) -> None:
        super().set_name(name, child_name_separator=child_name_separator)
        self.signal2.set_name("blah")

or by making an intermediate function that could be overridden instead (for 2):

class Derived(Base):
    def set_child_name(self, child, name):
        super().set_child_name(child, "blah" if child is self.signal2 else name)

I think 2 would cause less breakages, so I would favour that over 1, but I'd welcome thoughts on the best API to override the child name.

@DominicOram @DiamondJoseph @callumforrester @jwlodek thoughts?

Acceptance Criteria

• Code changed
• Only the single test that mimics @rtuck99's use case is changed