Add class for representing Power quantities

Signed-off-by: Sahas Subramanian <[email protected]>

Author: shsms

src/frequenz/sdk/timeseries/_quantities.py

@@ -268,3 +268,87 @@ def __eq__(self, other: object) -> bool:
         # doesn't help mypy identify the type of other,  so the below line is necessary.
         assert isinstance(other, self.__class__)
         return self._base_value == other._base_value
+
+
+class Power(
+    Quantity,
+    exponent_unit_map={
+        -3: "mW",
+        0: "W",
+        3: "kW",
+        6: "MW",
+    },
+):
+    """A power quantity."""
+
+    @classmethod
+    def from_watts(cls, watts: float) -> Self:
+        """Initialize a new power quantity.
+
+        Args:
+            watts: The power in watts.
+
+        Returns:
+            A new power quantity.
+        """
+        return cls(value=watts, exponent=0)
+
+    @classmethod
+    def from_milliwatts(cls, milliwatts: float) -> Self:
+        """Initialize a new power quantity.
+
+        Args:
+            milliwatts: The power in milliwatts.
+
+        Returns:
+            A new power quantity.
+        """
+        return cls(value=milliwatts, exponent=-3)
+
+    @classmethod
+    def from_kilowatts(cls, kilowatts: float) -> Self:
+        """Initialize a new power quantity.
+
+        Args:
+            kilowatts: The power in kilowatts.
+
+        Returns:
+            A new power quantity.
+        """
+        return cls(value=kilowatts, exponent=3)
+
+    @classmethod
+    def from_megawatts(cls, megawatts: float) -> Self:
+        """Initialize a new power quantity.
+
+        Args:
+            megawatts: The power in megawatts.
+
+        Returns:
+            A new power quantity.
+        """
+        return cls(value=megawatts, exponent=6)
+
+    def as_watts(self) -> float:
+        """Return the power in watts.
+
+        Returns:
+            The power in watts.
+        """
+        return self._base_value
+
+    def as_kilowatts(self) -> float:
+        """Return the power in kilowatts.
+
+        Returns:
+            The power in kilowatts.
+        """
+        return self._base_value / 1e3
+
+    def as_megawatts(self) -> float:
+        """Return the power in megawatts.
+
+        Returns:
+            The power in megawatts.
+        """
+        return self._base_value / 1e6

tests/timeseries/test_quantities.py

@@ -5,7 +5,7 @@
 
 import pytest
 
-from frequenz.sdk.timeseries._quantities import Quantity
+from frequenz.sdk.timeseries._quantities import Power, Quantity
 
 
 class Fz1(
@@ -146,3 +146,18 @@ def test_comparison() -> None:
         excinfo.value.args[0]
         == "'>=' not supported between instances of 'Fz1' and 'Fz2'"
     )
+
+
+def test_power() -> None:
+    """Test the power class."""
+    power = Power.from_milliwatts(0.0000002)
+    assert f"{power:.9}" == "0.0000002 mW"
+    power = Power.from_kilowatts(10000000.2)
+    assert f"{power}" == "10000 MW"
+
+    power = Power.from_kilowatts(1.2)
+    assert power.as_watts() == 1200.0
+    assert power.as_megawatts() == 0.0012
+    assert power == Power.from_milliwatts(1200000.0)
+    assert power == Power.from_megawatts(0.0012)
+    assert power != Power.from_watts(1000.0)