Make interface for BatteryPool metrics consistent with power methods (frequenz-floss#381)

The `soc`, `capacity`, `power_bounds` methods of the `BatteryPool`
were directly returning receivers.  They've now been converted to
properties, from which `new_receiver()` has to be called, to get a
receiver.

New:

``` python
soc_recv = battery_pool.soc.new_receiver()
```

Old:

``` python
soc_recv = battery_pool.soc()
```

Author: shsms

RELEASE_NOTES.md

@@ -16,6 +16,14 @@ This release drops support for Python versions older than 3.11.
 
 * Now `frequenz.sdk.timeseries.Sample` uses a more sensible comparison.  Before this release `Sample`s were compared only based on the `timestamp`.  This was due to a limitation in Python versions earlier than 3.10.  Now that the minimum supported version is 3.11 this hack is not needed anymore and `Sample`s are compared using both `timestamp` and `value` as most people probably expects.
 
+* `BatteryPool` metric streaming interfaces have changed for `soc`, `capacity` and `power_bounds`:
+
+  ```python
+  soc_rx = battery_pool.soc()    # old
+
+  soc_rx = battery_pool.soc.new_receiver()    # new
+  ```
+
 ## New Features
 
 <!-- Here goes the main new features and examples or instructions on how to use them -->

examples/battery_pool.py

@@ -33,9 +33,9 @@ async def main() -> None:
 
     battery_pool = microgrid.battery_pool()
     receivers: Dict[str, Receiver[Any]] = {
-        "soc": await battery_pool.soc(maxsize=1),
-        "capacity": await battery_pool.capacity(maxsize=1),
-        "power_bounds": await battery_pool.power_bounds(maxsize=1),
+        "soc": battery_pool.soc.new_receiver(maxsize=1),
+        "capacity": battery_pool.capacity.new_receiver(maxsize=1),
+        "power_bounds": battery_pool.power_bounds.new_receiver(maxsize=1),
     }
 
     merged_channel = MergeNamed[Any](**receivers)

src/frequenz/sdk/timeseries/battery_pool/_methods.py

@@ -13,7 +13,7 @@
 from frequenz.channels import Broadcast, Receiver
 
 from ..._internal._asyncio import cancel_and_await
-from ..._internal._constants import WAIT_FOR_COMPONENT_DATA_SEC
+from ..._internal._constants import RECEIVER_MAX_SIZE, WAIT_FOR_COMPONENT_DATA_SEC
 from ._component_metric_fetcher import (
     ComponentMetricFetcher,
     LatestBatteryMetricsFetcher,
@@ -25,7 +25,7 @@
 _logger = logging.getLogger(__name__)
 
 
-class AggregateMethod(Generic[T], ABC):
+class MetricAggregator(Generic[T], ABC):
     """Interface to control how the component data should be aggregated and send."""
 
     @abstractmethod
@@ -37,7 +37,9 @@ def update_working_batteries(self, new_working_batteries: set[int]) -> None:
         """
 
     @abstractmethod
-    def new_receiver(self, maxsize: int | None) -> Receiver[T | None]:
+    def new_receiver(
+        self, maxsize: int | None = RECEIVER_MAX_SIZE
+    ) -> Receiver[T | None]:
         """Return new receiver for the aggregated metric results.
 
         Args:
@@ -61,7 +63,7 @@ def name(cls) -> str:
         """
 
 
-class SendOnUpdate(AggregateMethod[T]):
+class SendOnUpdate(MetricAggregator[T]):
     """Wait for the change of the components metrics and send updated result.
 
     This method will cache the component metrics. When any metric change it will
@@ -110,7 +112,9 @@ def name(cls) -> str:
         """
         return "SendOnUpdate"
 
-    def new_receiver(self, maxsize: int | None) -> Receiver[T | None]:
+    def new_receiver(
+        self, maxsize: int | None = RECEIVER_MAX_SIZE
+    ) -> Receiver[T | None]:
         """Return new receiver for the aggregated metric results.
 
         Args:

src/frequenz/sdk/timeseries/battery_pool/battery_pool.py

@@ -14,7 +14,6 @@
 from frequenz.channels import Receiver, Sender
 
 from ..._internal._asyncio import cancel_and_await
-from ..._internal._constants import RECEIVER_MAX_SIZE
 from ...actor import ChannelRegistry, ComponentMetricRequest
 from ...actor.power_distributing._battery_pool_status import BatteryStatus
 from ...microgrid import connection_manager
@@ -25,7 +24,7 @@
     FormulaGeneratorConfig,
     FormulaType,
 )
-from ._methods import AggregateMethod, SendOnUpdate
+from ._methods import MetricAggregator, SendOnUpdate
 from ._metric_calculator import CapacityCalculator, PowerBoundsCalculator, SoCCalculator
 from ._result_types import CapacityMetrics, PowerMetrics, SoCMetrics
 
@@ -85,7 +84,7 @@ def __init__(  # pylint: disable=too-many-arguments
             )
 
         self._min_update_interval = min_update_interval
-        self._active_methods: dict[str, AggregateMethod[Any]] = {}
+        self._active_methods: dict[str, MetricAggregator[Any]] = {}
 
         self._namespace: str = f"battery-pool-{self._batteries}-{uuid.uuid4()}"
         self._formula_pool: FormulaEnginePool = FormulaEnginePool(
@@ -184,19 +183,19 @@ def consumption_power(self) -> FormulaEngine:
         assert isinstance(engine, FormulaEngine)
         return engine
 
-    async def soc(
-        self, maxsize: int | None = RECEIVER_MAX_SIZE
-    ) -> Receiver[SoCMetrics | None]:
+    @property
+    def soc(self) -> MetricAggregator[SoCMetrics]:
         """Get receiver to receive new soc metrics when they change.
 
-        Soc formulas are described in the receiver return type.
-        None will be send if there is no component to calculate metric.
+        Soc formulas are described in the receiver return type.  None will be send if
+        there is no component to calculate metric.
 
-        Args:
-            maxsize: Maxsize of the receiver channel.
+        A receiver from the MetricAggregator can be obtained by calling the
+        `new_receiver` method.
 
         Returns:
-            Receiver for this metric.
+            A MetricAggregator that will calculate and stream the aggregate soc of
+                all batteries in the pool.
         """
         method_name = SendOnUpdate.name() + "_" + SoCCalculator.name()
 
@@ -208,22 +207,21 @@ async def soc(
                 min_update_interval=self._min_update_interval,
             )
 
-        running_method = self._active_methods[method_name]
-        return running_method.new_receiver(maxsize)
+        return self._active_methods[method_name]
 
-    async def capacity(
-        self, maxsize: int | None = RECEIVER_MAX_SIZE
-    ) -> Receiver[CapacityMetrics | None]:
+    @property
+    def capacity(self) -> MetricAggregator[CapacityMetrics]:
         """Get receiver to receive new capacity metrics when they change.
 
-        Capacity formulas are described in the receiver return type.
-        None will be send if there is no component to calculate metrics.
+        Capacity formulas are described in the receiver return type.  None will be send
+        if there is no component to calculate metrics.
 
-        Args:
-            maxsize: Maxsize of the receiver channel.
+        A receiver from the MetricAggregator can be obtained by calling the
+        `new_receiver` method.
 
         Returns:
-            Receiver for this metric.
+            A MetricAggregator that will calculate and stream the capacity of all
+                batteries in the pool.
         """
         method_name = SendOnUpdate.name() + "_" + CapacityCalculator.name()
 
@@ -235,22 +233,21 @@ async def capacity(
                 min_update_interval=self._min_update_interval,
             )
 
-        running_method = self._active_methods[method_name]
-        return running_method.new_receiver(maxsize)
+        return self._active_methods[method_name]
 
-    async def power_bounds(
-        self, maxsize: int | None = RECEIVER_MAX_SIZE
-    ) -> Receiver[PowerMetrics | None]:
+    @property
+    def power_bounds(self) -> MetricAggregator[PowerMetrics]:
         """Get receiver to receive new power bounds when they change.
 
         Power bounds formulas are described in the receiver return type.
         None will be send if there is no component to calculate metrics.
 
-        Args:
-            maxsize: Maxsize of the receivers channel.
+        A receiver from the MetricAggregator can be obtained by calling the
+        `new_receiver` method.
 
         Returns:
-            Receiver for this metric.
+            A MetricAggregator that will calculate and stream the power bounds
+                of all batteries in the pool.
         """
         method_name = SendOnUpdate.name() + "_" + PowerBoundsCalculator.name()
 
@@ -262,8 +259,7 @@ async def power_bounds(
                 min_update_interval=self._min_update_interval,
             )
 
-        running_method = self._active_methods[method_name]
-        return running_method.new_receiver(maxsize)
+        return self._active_methods[method_name]
 
     async def stop(self) -> None:
         """Stop all pending async tasks."""

tests/timeseries/_battery_pool/test_battery_pool.py

@@ -500,7 +500,7 @@ async def run_capacity_test(setup_args: SetupArgs) -> None:
             sampling_rate=0.05,
         )
 
-    capacity_receiver = await battery_pool.capacity(maxsize=50)
+    capacity_receiver = battery_pool.capacity.new_receiver(maxsize=50)
 
     # First metrics delivers slower because of the startup delay in the pool.
     msg = await asyncio.wait_for(
@@ -633,7 +633,7 @@ async def run_soc_test(setup_args: SetupArgs) -> None:
             sampling_rate=0.05,
         )
 
-    receiver = await battery_pool.soc(maxsize=50)
+    receiver = battery_pool.soc.new_receiver(maxsize=50)
 
     # First metrics delivers slower because of the startup delay in the pool.
     msg = await asyncio.wait_for(
@@ -775,7 +775,7 @@ async def run_power_bounds_test(  # pylint: disable=too-many-locals
             sampling_rate=0.1,
         )
 
-    receiver = await battery_pool.power_bounds(maxsize=50)
+    receiver = battery_pool.power_bounds.new_receiver(maxsize=50)
 
     # First metrics delivers slower because of the startup delay in the pool.
     msg = await asyncio.wait_for(