Merge pull request #34 from openforcefield/quantity-to-openmm

Add `Quantity.to_openmm`

docs/conf.py

@@ -96,6 +96,8 @@
 napoleon_google_docstring = True
 napoleon_use_param = False
 napoleon_use_ivar = True
+napoleon_use_rtype = False
+napoleon_preprocess_types = True
 
 myst_enable_extensions = [
     "deflist",

openff/units/tests/test_units.py

@@ -6,6 +6,21 @@
 from openff.units import unit
 
 
+class TestQuantity:
+    @skip_if_missing("openmm.unit")
+    def test_to_openmm_method(self):
+        """
+        Test the basic behavior of `Quantity.to_openmm` as an API call. Testing of the underlying
+        behavior of the standalone `to_openmm` function is in opeff/units/tests/test_openmm.py.
+        """
+        from openmm import unit as openmm_unit
+
+        quantity = unit.Quantity(0.5, "nanometer")
+        converted = quantity.to_openmm()
+
+        assert converted == openmm_unit.Quantity(0.5, openmm_unit.nanometer)
+
+
 class TestPickle:
     """Test pickle-based serialization of Quantity, Unit, and Measurement objects
 

openff/units/units.py

@@ -4,14 +4,19 @@
 
 import uuid
 import warnings
+from typing import TYPE_CHECKING
 
 import pint
+from openff.utilities import requires_package
 from pint.measurement import _Measurement
 from pint.quantity import _Quantity
 from pint.unit import _Unit
 
 from openff.units.utilities import get_defaults_path
 
+if TYPE_CHECKING:
+    from openmm.unit import Quantity as OpenMMQuantity
+
 __all__ = [
     "DEFAULT_UNIT_REGISTRY",
     "Quantity",
@@ -63,6 +68,19 @@ def _dask_finalize(results, func, args, units):
         values = func(results, *args)
         return Quantity(values, units)
 
+    @requires_package("openmm")
+    def to_openmm(self) -> "OpenMMQuantity":
+        """Convert the quantity to an ``openmm.unit.Quantity``.
+
+        Returns
+        -------
+        openmm_quantity : openmm.unit.quantity.Quantity
+            The OpenMM compatible quantity.
+        """
+        from openff.units.openmm import to_openmm
+
+        return to_openmm(self)
+
 
 class Measurement(_Measurement):
     """A value with associated units and uncertainty."""

setup.cfg

@@ -50,5 +50,8 @@ ignore_missing_imports = True
 [mypy-openmm]
 ignore_missing_imports = True
 
+[mypy-openmm.unit]
+ignore_missing_imports = True
+
 [mypy-openmm.app.element]
 ignore_missing_imports = True