feat: Register unit without updating config files

src/ansys/units/__init__.py

@@ -43,7 +43,7 @@
 from ansys.units.quantity import Quantity, get_si_value  # noqa: F401
 from ansys.units.systems import UnitSystem  # noqa: F401
 from ansys.units.unit import Unit  # noqa: F401
-from ansys.units.unit_registry import UnitRegistry  # noqa: F401
+from ansys.units.unit_registry import UnitRegistry, register_unit  # noqa: F401
 
 _THIS_DIRNAME = os.path.dirname(__file__)
 _README_FILE = os.path.normpath(os.path.join(_THIS_DIRNAME, "docs", "README.rst"))

src/ansys/units/unit_registry.py

@@ -25,7 +25,41 @@
 
 import yaml
 
-from ansys.units import Unit
+from ansys.units import Unit, _base_units, _derived_units
+
+
+def register_unit(unit: str, composition: str, factor):
+    """
+    Register a customized unit.
+
+    Parameters
+    ----------
+    unit: str
+        Name of the unit
+    composition: str
+        String chain of combined units
+    factor: float
+        Scaling factor
+
+    Examples
+    --------
+    >>> from ansys.units import register_unit
+    >>> register_unit(unit="Q", composition="N m", factor=1)
+    >>> ureg = UnitRegistry()
+    >>> ureg.Q
+    _name: Q
+    _dimensions: {'MASS': 1.0, 'LENGTH': 2.0, 'TIME': -2.0}
+    _composition: N m
+    _factor: 1
+    _si_units: kg m^2 s^-2
+    _si_scaling_factor: 1.0
+    _si_offset: 0.0
+    """
+    if unit in _base_units or unit in _derived_units:
+        raise UnitAlreadyRegistered(unit)
+    else:
+        register = {unit: {"composition": composition, "factor": factor}}
+        _derived_units.update(register)
 
 
 class UnitRegistry:
@@ -55,17 +89,19 @@ class UnitRegistry:
 
     def __init__(self, config="cfg.yaml", other: dict = None):
         unitdict = other or {}
+        global _derived_units
+        unitdict.update(_derived_units)
 
         if config:
             file_dir = os.path.dirname(__file__)
             qc_path = os.path.join(file_dir, config)
 
             with open(qc_path, "r") as qc_yaml:
                 qc_data = yaml.safe_load(qc_yaml)
-                _base_units: dict = qc_data["base_units"]
-                _derived_units: dict = qc_data["derived_units"]
+                _qc_base_units: dict = qc_data["base_units"]
+                _qc_derived_units: dict = qc_data["derived_units"]
 
-            unitdict.update(**_base_units, **_derived_units)
+            unitdict.update(**_qc_base_units, **_qc_derived_units)
 
         for unit in unitdict:
             setattr(self, unit, Unit(unit, unitdict[unit]))

tests/test_unit_registry.py

@@ -25,7 +25,7 @@
 
 import pytest
 
-from ansys.units import Unit, UnitRegistry, _base_units
+from ansys.units import Unit, UnitRegistry, _base_units, register_unit
 from ansys.units.unit_registry import UnitAlreadyRegistered
 
 
@@ -97,6 +97,22 @@ def test_immutability():
         ur.m = Unit("ft")
 
 
+def test_register_unit():
+    register_unit(unit="Q", composition="N m", factor=1)
+    ur = UnitRegistry()
+    assert ur.Q == ur.J
+
+    with pytest.raises(UnitAlreadyRegistered):
+        register_unit(unit="Q", composition="N m", factor=1)
+
+    register_unit(unit="Z", composition="N m", factor=1)
+    with pytest.raises(AttributeError):
+        ur.Z
+
+    ur = UnitRegistry()
+    assert ur.Q == ur.J == ur.Z
+
+
 def test_error_message():
     e1 = UnitAlreadyRegistered("kg")
     expected_str = "Unable to override `kg` it has already been registered."