How to save (pickle) a model instance in pyomo

Question

I want to create a model instance and then save it so I can load and solve at a later time (the initialization takes quite long compared to the solving). When I tried this i

Answer 1

The solution is the cloudpickle module, regular pickle has problems pickling functions. An example:

import cloudpickle

with open('test.pkl', mode='wb') as file:
   cloudpickle.dump(instance, file)


with open('test.pkl', mode='rb') as file:
   instance = cloudpickle.load(file)

Answer 2

It looks like pickle (and also cloudpickle) will not work when DerivativeVar is used.

from pyomo.environ import *
from pyomo.dae import *
import pickle
import dill
model = ConcreteModel()
model.x = ContinuousSet(initialize=(0., 1.))
model.y = Var(model.x, initialize=1.)
with open('model1.pickle', 'wb') as f:
    pickle.dump(model, f)

model.dydx = DerivativeVar(model.y, wrt=model.x)
with open('model2.pickle', 'wb') as f:
    try:
        pickle.dump(model, f)
    except TypeError:
        dill.dump(model, f)

dill appears to work instead for pickling a weakref: Pickling weakref in Python