Add initial code imported from the SDK

README.md

@@ -17,6 +17,11 @@ converting one of them.
 Quantities store the value in a base unit, and then provide methods to get that
 quantity as a particular unit.
 
+## Documentation
+
+For more information on how to use this library and examples, please check the
+[Documentation website](https://frequenz-floss.github.io/frequenz-quantities-python/).
+
 ## Supported Platforms
 
 The following platforms are officially supported (tested):

docs/index.md

@@ -1 +1,9 @@
---8<-- "README.md"
+# Frequenz Quantities Library
+
+::: frequenz.quantities
+    options:
+        members: []
+        show_bases: false
+        show_root_heading: false
+        show_root_toc_entry: false
+        show_source: false

pyproject.toml

@@ -80,6 +80,7 @@ dev-pytest = [
   "pytest-mock == 3.14.0",
   "pytest-asyncio == 0.23.7",
   "async-solipsism == 0.6",
+  "hypothesis == 6.100.2",
 ]
 dev = [
   "frequenz-quantities[dev-mkdocs,dev-flake8,dev-formatting,dev-mkdocs,dev-mypy,dev-noxfile,dev-pylint,dev-pytest]",

src/frequenz/quantities/__init__.py

@@ -3,23 +3,96 @@
 
 """Types for holding quantities with units.
 
-TODO(cookiecutter): Add a more descriptive module description.
-"""
+This library provide types for holding quantities with units. The main goal is to avoid
+mistakes while working with different types of quantities, for example avoiding adding
+a length to a time.
+
+It also prevents mistakes when operating between the same quantity but in different
+units, like adding a power in Joules to a power in Watts without converting one of them.
+
+Quantities store the value in a base unit, and then provide methods to get that quantity
+as a particular unit. They can only be constructed using special constructors with the
+form `Quantity.from_<unit>`, for example
+[`Power.from_watts(10.0)`][frequenz.quantities.Power.from_watts].
+
+Internally quantities store values as `float`s, so regular [float issues and limitations
+apply](https://docs.python.org/3/tutorial/floatingpoint.html), although some of them are
+tried to be mitigated.
+
+Quantities are also immutable, so operations between quantities return a new instance of
+the quantity.
+
+This library provides the following types:
+
+- [Current][frequenz.quantities.Current]: A quantity representing an electric current.
+- [Energy][frequenz.quantities.Energy]: A quantity representing energy.
+- [Frequency][frequenz.quantities.Frequency]: A quantity representing frequency.
+- [Percentage][frequenz.quantities.Percentage]: A quantity representing a percentage.
+- [Power][frequenz.quantities.Power]: A quantity representing power.
+- [Temperature][frequenz.quantities.Temperature]: A quantity representing temperature.
+- [Voltage][frequenz.quantities.Voltage]: A quantity representing electric voltage.
 
+There is also the unitless [Quantity][frequenz.quantities.Quantity] class. All
+quantities are subclasses of this class and it can be used as a base to create new
+quantities. Using the `Quantity` class directly is discouraged, as it doesn't provide
+any unit conversion methods.
 
-# TODO(cookiecutter): Remove this function
-def delete_me(*, blow_up: bool = False) -> bool:
-    """Do stuff for demonstration purposes.
+Example:
+    ```python
+    from datetime import timedelta
+    from frequenz.quantities import Power, Voltage, Current, Energy
+
+    # Create a power quantity
+    power = Power.from_watts(230.0)
+
+    # Printing uses a unit to make the string as short as possible
+    print(f"Power: {power}")  # Power: 230.0 W
+    # The precision can be changed
+    print(f"Power: {power:0.3}")  # Power: 230.000 W
+    # The conversion methods can be used to get the value in a particular unit
+    print(f"Power in MW: {power.as_megawatt()}")  # Power in MW: 0.00023 MW
+
+    # Create a voltage quantity
+    voltage = Voltage.from_volts(230.0)
+
+    # Calculate the current
+    current = power / voltage
+    assert isinstance(current, Current)
+    print(f"Current: {current}")  # Current: 1.0 A
+    assert current.isclose(Current.from_amperes(1.0))
+
+    # Calculate the energy
+    energy = power * timedelta(hours=1)
+    assert isinstance(energy, Energy)
+    print(f"Energy: {energy}")  # Energy: 230.0 Wh
+    print(f"Energy in kWh: {energy.as_kilowatt_hours()}") # Energy in kWh: 0.23
+
+    # Invalid operations are not permitted
+    # (when using a type hinting linter like mypy, this will be caught at linting time)
+    try:
+        power + voltage
+    except TypeError as e:
+        print(f"Error: {e}")  # Error: unsupported operand type(s) for +: 'Power' and 'Voltage'
+    ```
+"""
 
-    Args:
-        blow_up: If True, raise an exception.
 
-    Returns:
-        True if no exception was raised.
+from ._current import Current
+from ._energy import Energy
+from ._frequency import Frequency
+from ._percentage import Percentage
+from ._power import Power
+from ._quantity import Quantity
+from ._temperature import Temperature
+from ._voltage import Voltage
 
-    Raises:
-        RuntimeError: if blow_up is True.
-    """
-    if blow_up:
-        raise RuntimeError("This function should be removed!")
-    return True
+__all__ = [
+    "Current",
+    "Energy",
+    "Frequency",
+    "Percentage",
+    "Power",
+    "Quantity",
+    "Temperature",
+    "Voltage",
+]

src/frequenz/quantities/_current.py

@@ -0,0 +1,131 @@
+# License: MIT
+# Copyright © 2022 Frequenz Energy-as-a-Service GmbH
+
+"""Types for holding quantities with units."""
+
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Self, overload
+
+from ._quantity import NoDefaultConstructible, Quantity
+
+if TYPE_CHECKING:
+    from ._percentage import Percentage
+    from ._power import Power
+    from ._voltage import Voltage
+
+
+class Current(
+    Quantity,
+    metaclass=NoDefaultConstructible,
+    exponent_unit_map={
+        -3: "mA",
+        0: "A",
+    },
+):
+    """A current quantity.
+
+    Objects of this type are wrappers around `float` values and are immutable.
+
+    The constructors accept a single `float` value, the `as_*()` methods return a
+    `float` value, and each of the arithmetic operators supported by this type are
+    actually implemented using floating-point arithmetic.
+
+    So all considerations about floating-point arithmetic apply to this type as well.
+    """
+
+    @classmethod
+    def from_amperes(cls, amperes: float) -> Self:
+        """Initialize a new current quantity.
+
+        Args:
+            amperes: The current in amperes.
+
+        Returns:
+            A new current quantity.
+        """
+        return cls._new(amperes)
+
+    @classmethod
+    def from_milliamperes(cls, milliamperes: float) -> Self:
+        """Initialize a new current quantity.
+
+        Args:
+            milliamperes: The current in milliamperes.
+
+        Returns:
+            A new current quantity.
+        """
+        return cls._new(milliamperes, exponent=-3)
+
+    def as_amperes(self) -> float:
+        """Return the current in amperes.
+
+        Returns:
+            The current in amperes.
+        """
+        return self._base_value
+
+    def as_milliamperes(self) -> float:
+        """Return the current in milliamperes.
+
+        Returns:
+            The current in milliamperes.
+        """
+        return self._base_value * 1e3
+
+    # See comment for Power.__mul__ for why we need the ignore here.
+    @overload  # type: ignore[override]
+    def __mul__(self, scalar: float, /) -> Self:
+        """Scale this current by a scalar.
+
+        Args:
+            scalar: The scalar by which to scale this current.
+
+        Returns:
+            The scaled current.
+        """
+
+    @overload
+    def __mul__(self, percent: Percentage, /) -> Self:
+        """Scale this current by a percentage.
+
+        Args:
+            percent: The percentage by which to scale this current.
+
+        Returns:
+            The scaled current.
+        """
+
+    @overload
+    def __mul__(self, other: Voltage, /) -> Power:
+        """Multiply the current by a voltage to get a power.
+
+        Args:
+            other: The voltage.
+
+        Returns:
+            The calculated power.
+        """
+
+    def __mul__(self, other: float | Percentage | Voltage, /) -> Self | Power:
+        """Return a current or power from multiplying this current by the given value.
+
+        Args:
+            other: The scalar, percentage or voltage to multiply by.
+
+        Returns:
+            A current or power.
+        """
+        from ._percentage import Percentage  # pylint: disable=import-outside-toplevel
+        from ._power import Power  # pylint: disable=import-outside-toplevel
+        from ._voltage import Voltage  # pylint: disable=import-outside-toplevel
+
+        match other:
+            case float() | Percentage():
+                return super().__mul__(other)
+            case Voltage():
+                return Power._new(self._base_value * other._base_value)
+            case _:
+                return NotImplemented