ImportError of a custom script

[Daveonwave]

I'm trying to create a fmu of a custom class. My code is structured like this:

from pythonfmu.fmi2slave import Fmi2Slave, Fmi2Causality, Fmi2Variability, Real

try:
    import MyModel as mymodel
    from sympy import symbols, exp
except ImportError:
    symbols, exp, mymodel = None, None, None


class MyFmu(Fmi2Slave):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.input_var = 0.
        self.output_var = 0.

        self.model = mymodel.ModelClass(...)

        self.register_variable(Real('input_var', causality=Fmi2Causality.input))
        self.register_variable(Real('output_var', causality=Fmi2Causality.output))

    def do_step(self, current_time, step_size) -> bool:
        self.output_var = self.model.step(...)
        return True

I followed the sympyslave.py structure to declare the imports, even if I don't plan to use sympy.

My problem is related to the import of MyModel.py script, which is a custom script that I would like to wrap with fmu.

I'm trying to export the fmu with this command pythonfmu build -f MyFmu.py MyModel.py because I'm considering MyModel.py as a project file, but it's not working since I'm getting the error AttributeError: 'NoneType' object has no attribute 'Model'.

Am I missing something or is it just unfeasible to import a custom class in this way?
Thanks in advance for the help.

[markaren]

Do you have sympy installed? Otherwise the code would raise an ImportError (and mymodel set to None)...

[Daveonwave]

Yes, sympy is correctly installed and I also tried to comment out lines of code related to sympy import. In both cases I still get the ImportError

[markaren]

You could try debugging the issue by extracting the FMU content and run the Python code directly (as any othe python code).

[Daveonwave]

Thanks, calling the build_FMU method of FmuBuilder class it seems to work even without declaring additional project files and the output of the simulation is the expected one.

[markaren]

Oh, you got the error while exporting the FMU.... And it works when doing it programatically. Are you sure you were using the same python environment for both cases?

[Daveonwave]

Sure, I double checked it again just to be sure, but the python interpreter/version is the same (Python 3.8) and I didn't create a venv, so packages match perfectly.