def test_dimensionless_units():
assert utils.string_to_unit('dimensionless') == unit.dimensionless
unit_string = utils.unit_to_string(unit.dimensionless)
unit_value = utils.string_to_unit(unit_string)
assert unit_value == unit.dimensionless
def openmm_unit_to_pint(openmm_unit):
"""Converts a `simtk.unit.Unit` to a `pint.Unit`.
Parameters
----------
openmm_unit: simtk.unit.Unit
The unit to convert.
Returns
-------
pint.Unit
The converted unit.
"""
from openforcefield.utils import unit_to_string
if openmm_unit is None or isinstance(openmm_unit, UndefinedAttribute):
return None
assert isinstance(openmm_unit, simtk_unit.Unit)
if openmm_unit in unsupported_openmm_units:
raise ValueError(
f"Quantities bearing the {openmm_unit} are not "
f"currently supported by pint."
)
openmm_unit_string = unit_to_string(openmm_unit)
# Handle the case whereby OMM treats daltons as having
# units of g / mol, whereas SI and pint define them to
# have units of kg.
openmm_unit_string = (
None
if openmm_unit_string is None
else openmm_unit_string.replace("dalton", "(gram / mole)")
)
try:
pint_unit = unit(openmm_unit_string).units
except UndefinedUnitError:
logger.info(
f"The {openmm_unit_string} OMM unit string (based on the {openmm_unit} object) "
f"is undefined in pint"
)
raise
return pint_unit