Description
Summary
When trying to assign a value to a Pyomo Var using set_value with a pint Quantity as the argument, the following error is returned: pyomo.core.base.units_container.UnitsError: Cannot convert None to m. Units are not compatible. (see below for example and full stack trace).
Steps to reproduce the issue
import pyomo.environ as pyo
import pint
m = pyo.ConcreteModel()
m.v = pyo.Var(initialize=1, units=pyo.units.m)
ureg = pint.UnitRegistry()
Q = 3 * ureg.meter
m.v.set_value(Q)
Error Message
WARNING: Dynamically registering the following numeric type:
Quantity
Dynamic registration is supported for convenience, but there are known
limitations to this approach. We recommend explicitly registering numeric
types using the following functions:
RegisterNumericType(), RegisterIntegerType(), RegisterBooleanType().
Traceback (most recent call last):
File "/home/andrew/idaes/testing/issue_test.py", line 10, in
m.v.set_value(Q)
File "/home/andrew/pyomo/pyomo/pyomo/core/base/var.py", line 371, in set_value
val = units.convert_value(
File "/home/andrew/pyomo/pyomo/pyomo/core/base/units_container.py", line 1289, in convert_value
raise UnitsError(
pyomo.core.base.units_container.UnitsError: Cannot convert None to m. Units are not compatible.
Additional information
The root cause of the issue appears be in units.get_value. Line 370 in var.py (_src_units = units.get_units(val)) is returning None when provided with a pint Quantity, rather than the desired units from the Quantity. This then causes the error checking in units.convert_value to fail with the observed error due to the apparent inconsistent units, hence the Cannot convert None to m.