ENH: add ability to control component names are mangled

The Python name (via attributes) of a child device is `foo.bar.baz`, however
for a number of historical reasons (allowed keys in mongo and for attribute
access in Pandas data frames with columns named from the data keys in an event
stream) ophyd-sync has replaced '.' with '_' in the names.  This leads to
ambiguity when looking at the (default) name to which component on which device
the data came from as there may be `_` in the attribute names.  Ophyd-async
used '-' which does allow for round tripping.

This makes it controllable on per-instance basis in ophyd-sync so that users
can either make a different set of trade offs.

xref bluesky/ophyd-async#666

ophyd/device.py

@@ -253,10 +253,12 @@ def create_component(self, instance):
         "Instantiate the object described by this Component for a Device"
         kwargs = self.kwargs.copy()
         kwargs.update(
-            name=f"{instance.name}_{self.attr}",
+            name=f"{instance.name}{instance._child_name_seperator}{self.attr}",
             kind=instance._component_kinds[self.attr],
             attr_name=self.attr,
         )
+        if issubclass(self.cls, Device):
+            kwargs.setdefault('child_name_seperator', instance._child_name_seperator)
 
         for kw, val in list(kwargs.items()):
             kwargs[kw] = self.maybe_add_prefix(instance, kw, val)
@@ -839,10 +841,11 @@ def __init__(
         read_attrs=None,
         configuration_attrs=None,
         parent=None,
+        child_name_seperator='_',
         **kwargs,
     ):
         self._destroyed = False
-
+        self._child_name_seperator = child_name_seperator
         # Store EpicsSignal objects (only created once they are accessed)
         self._signals = {}
 

ophyd/tests/test_device.py

@@ -969,3 +969,31 @@ class FakeTriggerableDevice(Device):
 
     d.trigger()
     assert d.strigger.get() == after
+
+
+def test_child_seperator():
+    class Test(Device):
+        a = Component(Signal)
+        b = Component(Signal)
+
+    t = Test(name="bob")
+    assert t.a.name == "bob_a"
+
+    t = Test(name="bob", child_name_seperator="-")
+    assert t.a.name == "bob-a"
+
+    class Test2(Device):
+        c = Component(Signal)
+        d = Component(Signal)
+        t = Component(Test)
+        s = Component(Test, child_name_seperator="?")
+
+    t2 = Test2(name="bob", child_name_seperator="!")
+
+    assert t2.c.name == "bob!c"
+    assert t2.d.name == "bob!d"
+
+    assert t2.t.a.name == "bob!t!a"
+    assert t2.t.b.name == "bob!t!b"
+    assert t2.s.a.name == "bob!s?a"
+    assert t2.s.a.name == "bob!s?b"