PythonFMU3

A lightweight framework that enables the packaging of Python 3 code as FMUs (following FMI version 3.0).

This project is a fork of the original PythonFMU repository available at https://github.com/NTNU-IHB/PythonFMU, which was used as the basis for adding support for FMI 3.0. While we have made efforts to expand the functionality of this project, it currently has some limitations and does not support all the features of FMI 3.0. We would like to acknowledge and give credit to the original PythonFMU project for their contributions to this work.

Support:

Both the Model Exchange and Co-simulation interfaces are supported, with Float64, Int32, Int64, UInt64, Boolean, String and Enumeration variables (plus NumPy arrays of the numeric types). See the documentation for the full list of supported features and current limitations, and the examples folder for more models.

See the changelog for what changed in each release.

Where can I run the FMU?

In any FMI 3.0 importer: Python-based tools such as FMPy, and native tools such as OMSimulator, fmusim or Simulink.

The machine running the simulation needs Python 3 with a shared Python library, plus the packages your model imports (see pythonfmu3 deploy below). Inside a Python-based importer the FMU uses that interpreter. Otherwise, on Linux and macOS the FMU finds and loads libpython itself; if it picks the wrong one, or none, point it at the right library:

export PYTHONFMU_PYTHON_LIBRARY=/usr/lib/x86_64-linux-gnu/libpython3.12.so.1.0

On Windows, python3.dll must be on the PATH. See Running FMUs outside Python for the full lookup order.

How do I build an FMU from python code?

1. Install pythonfmu3 package:

pip install pythonfmu3

2. Create a new class extending the Fmi3Slave class declared in the pythonfmu3.fmi3slave module (see below for an example). Keep a single FMU class per script.
3. Run pythonfmu3 build to create the fmu.

usage: pythonfmu3 build [-h] -f SCRIPT_FILE [-d DEST] [--doc DOCUMENTATION_FOLDER] [--terminals TERMINALS]
                        [--no-external-tool] [--only-one-per-process] [--handle-state] [--serialize-state]
                        [--no-variable-step] [--needs-completed-step]
                        [Project files ...]

Build an FMU from a Python script.

positional arguments:
  Project files         Additional project files required by the Python script.

options:
  -h, --help            show this help message and exit
  -f SCRIPT_FILE, --file SCRIPT_FILE
                        Path to the Python script.
  -d DEST, --dest DEST  Where to save the FMU.
  --doc DOCUMENTATION_FOLDER
                        Documentation folder to include in the FMU.
  --terminals TERMINALS
                        Terminals file (terminalsAndIcons.xml) to include in the FMU.
  --no-external-tool    If given, needsExecutionTool=false
  --only-one-per-process
                        If given, canBeInstantiatedOnlyOncePerProcess=true
  --handle-state        If given, canGetAndSetFMUState=true
  --serialize-state     If given, canSerializeFMUState=true
  --no-variable-step    If given, canHandleVariableCommunicationStepSize=false
  --needs-completed-step
                        If given, needsCompletedIntegratorStep=true

How do I build an FMU from python code with third-party dependencies?

Often, Python scripts depends on non-builtin libraries like numpy, scipy, etc. PythonFMU does not package a full environment within the FMU. However, you can package a requirements.txt or environment.yml file within your FMU following these steps:

1. Install pythonfmu package: pip install pythonfmu3
2. Create a new class extending the Fmi3Slave class declared in the pythonfmu3.fmi3slave module (see the examples below).
3. Create a requirements.txt file (to use pip manager) and/or a environment.yml file (to use conda manager) that defines your dependencies.
4. Run pythonfmu3 build -f myscript.py requirements.txt to create the fmu including the dependencies file.

And using pythonfmu3 deploy, end users will be able to update their local Python environment. The steps to achieve that:

1. Install pythonfmu package: pip install pythonfmu3
2. Be sure to be in the Python environment to be updated. Then execute pythonfmu3 deploy -f my.fmu

usage: pythonfmu3 deploy [-h] -f FMU [-e ENVIRONMENT] [{pip,conda}]

Deploy a Python FMU. The command will look in the `resources` folder for one of the following files:
`requirements.txt` or `environment.yml`. If you specify a environment file but no package manager, `conda` will be selected for `.yaml` and `.yml` otherwise `pip` will be used. The tool assume the Python environment in which the FMU should be executed is the current one.

positional arguments:
  {pip,conda}           Python packages manager

optional arguments:
  -h, --help            show this help message and exit
  -f FMU, --file FMU    Path to the Python FMU.
  -e ENVIRONMENT, --env ENVIRONMENT
                        Requirements or environment file.

Cosimulation Example:

Write the script

from pythonfmu3 import Fmi3Causality, Fmi3Slave, Boolean, Int32, Float64, String


class PythonSlave(Fmi3Slave):

    def __init__(self, **kwargs):
        super().__init__(**kwargs)

        self.author = "John Doe"
        self.description = "A simple description"

        # Create attributes before registering them: register_variable only adds a setter
        # (needed for inputs and parameters) for attributes that already exist.
        self.time = 0.0
        self.intOut = 1
        self.realOut = 3.0
        self.booleanVariable = True
        self.stringVariable = "Hello World!"
        self.register_variable(Float64("time", causality=Fmi3Causality.independent))
        self.register_variable(Int32("intOut", causality=Fmi3Causality.output))
        self.register_variable(Float64("realOut", causality=Fmi3Causality.output))
        self.register_variable(Boolean("booleanVariable", causality=Fmi3Causality.local))
        self.register_variable(String("stringVariable", causality=Fmi3Causality.local))
        
        # Note:
        # it is also possible to explicitly define getters and setters as lambdas in case the variable is not backed by a Python field.
        # self.register_variable(Float64("myReal", causality=Fmi3Causality.output, getter=lambda: self.realOut, setter=lambda v: set_real_out(v))

    def do_step(self, current_time, step_size):
        return True

Create the FMU

pythonfmu3 build -f pythonslave.py myproject

In this example a python class named PythonSlave that extends Fmi3Slave is declared in a file named pythonslave.py, where myproject is an optional folder containing additional project files required by the python script. Project folders such as this will be recursively copied into the FMU. Multiple project files/folders may be added.

Model Exchange Example

To create a model exchange FMU you must inherit from Fmi3SlaveBase and one of (or both) mixin classes ModelExchange or CoSimulation.

Write the script

from pythonfmu3 import Fmi3Causality, Fmi3Initial, Fmi3SlaveBase, Fmi3Variability, Float64, ModelExchange
from typing import List


class PythonSlaveMX(Fmi3SlaveBase, ModelExchange):

    def __init__(self, **kwargs):
        super().__init__(**kwargs)

        self.author = "John Doe"
        self.description = "A simple description"

        self.time = 0.0
        self.mu = 1.0
        self.x0 = 2
        self.x1 = 0
        self.derx0 = 0.0
        self.derx1 = 0.0

        self.register_variable(Float64("time", causality=Fmi3Causality.independent, variability=Fmi3Variability.continuous))
        self.register_variable(Float64("x0", causality=Fmi3Causality.output, start=2, variability=Fmi3Variability.continuous, initial=Fmi3Initial.exact))
        self.register_variable(Float64("x1", causality=Fmi3Causality.output, start=0, variability=Fmi3Variability.continuous, initial=Fmi3Initial.exact))
        self.register_variable(Float64("derx0", causality=Fmi3Causality.local, variability=Fmi3Variability.continuous, derivative=1))
        self.register_variable(Float64("derx1", causality=Fmi3Causality.local, variability=Fmi3Variability.continuous, derivative=2))
        self.register_variable(Float64("mu", causality=Fmi3Causality.parameter, variability=Fmi3Variability.fixed))


    def get_continuous_state_derivatives(self) -> List[float]:
        self.derx0 = self.x1
        self.derx1 = self.mu * ((1 - self.x0**2) * self.x1) - self.x0
        return [self.derx0, self.derx1]
        

Note: Model Exchange classes must define a self.time member. Derivative variables give the value reference of their state with derivative=; value references are assigned in registration order starting at 0 (here time = 0, x0 = 1, x1 = 2).

Create the FMU

pythonfmu3 build -f pythonslaveMX.py