Allow equality comparisons for signal (#524)

* Allow equality comparisons for signal

These comparisons are needed by trigger_and_read for example.

* Entirely remove _fail() on comparisons

src/ophyd_async/core/_signal.py

@@ -45,15 +45,6 @@ async def wrapper(self: Signal, *args, **kwargs):
  return wrapper
 
 
-def _fail(self, other, *args, **kwargs):
- if isinstance(other, Signal):
- raise TypeError(
- "Can't compare two Signals, did you mean await signal.get_value() instead?"
- )
- else:
- return NotImplemented
-
-
 class Signal(Device, Generic[T]):
  """A Device with the concept of a value, with R, RW, W and X flavours"""
 
@@ -118,12 +109,6 @@ def source(self) -> str:
  """Like ca://PV_PREFIX:SIGNAL, or "" if not set"""
  return self._backend.source(self.name)
 
- __lt__ = __le__ = __eq__ = __ge__ = __gt__ = __ne__ = _fail
-
- def __hash__(self):
- # Restore the default implementation so we can use in a set or dict
- return hash(id(self))
-
 
 class _SignalCache(Generic[T]):
  def __init__(self, backend: SignalBackend[T], signal: Signal):

tests/core/test_signal.py

@@ -1,6 +1,5 @@
 import asyncio
 import logging
-import re
 import time
 from asyncio import Event
 from unittest.mock import ANY
@@ -37,26 +36,6 @@
 from ophyd_async.plan_stubs import ensure_connected
 
 
-async def test_signals_equality_raises():
- s1 = epics_signal_rw(int, "pva://pv1", name="signal")
- s2 = epics_signal_rw(int, "pva://pv2", name="signal")
- await s1.connect(mock=True)
- await s2.connect(mock=True)
-
- with pytest.raises(
- TypeError,
- match=re.escape(
- "Can't compare two Signals, did you mean await signal.get_value() instead?"
- ),
- ):
- s1 == s2
- with pytest.raises(
- TypeError,
- match=re.escape("'>' not supported between instances of 'SignalRW' and 'int'"),
- ):
- s1 > 4
-
-
 async def test_signal_can_be_given_backend_on_connect():
  sim_signal = SignalR()
  backend = MockSignalBackend(int)