PythonFMU

A lightweight framework that enables the packaging of Python3.x code as co-simulation FMUs.

How do I build an FMU from python code?

1. Install pythonfmu package:

pip install pythonfmu

2. Create a new class extending the Fmi2Slave class declared in the pythonfmu.fmi2slave module (see below for an example).
3. Run pythonfmu-builder to create the fmu.

usage: pythonfmu-builder [-h] -f SCRIPT_FILE [-d DEST] [--doc DOCUMENTATION_FOLDER]
                         [--no-external-tool] [--no-variable-step] [--interpolate-inputs] [--only-one-per-process]
                         [--handle-state] [--serialize-state] [--use-memory-management]
                         [Project files [Project files ...]]

Build a FMU from a Python script.

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

optional arguments:
  -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.

  --no-external-tool    If given, needsExecutionTool=false
  --no-variable-step    If given, canHandleVariableCommunicationStepSize=false
  --interpolate-inputs  If given, canInterpolateInputs=true
  --only-one-per-process
                        If given, canBeInstantiatedOnlyOncePerProcess=true
  --handle-state        If given, canGetAndSetFMUstate=true
  --serialize-state     If given, canSerializeFMUstate=true
  --use-memory-management
                        If given, canNotUseMemoryManagementFunctions=false

Example:

Write the script

from pythonfmu import Fmi2Causality, Fmi2Slave, Boolean, Integer, Real, String

slave_class = "PythonSlave"  # REQUIRED - Name of the class extending Fmi2Slave


class PythonSlave(Fmi2Slave):

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

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

        self.intOut = 1
        self.realOut = 3.0
        self.booleanVariable = True
        self.stringVariable = "Hello World!"
        self.register_variable(Integer("intOut", causality=Fmi2Causality.output))
        self.register_variable(Real("realOut", causality=Fmi2Causality.output))
        self.register_variable(Boolean("booleanVariable", causality=Fmi2Causality.local))
        self.register_variable(String("stringVariable", causality=Fmi2Causality.local))

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

Create the FMU

pythonfmu-builder -f pythonslave.py pythonfmu

In this example a python class named PythonSlave that extends Fmi2Slave is declared in a file named pythonslave.py, where pythonfmu 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.

Test it online

Note

PythonFMU does not bundle Python, which makes it a tool coupling solution. This means that you can not expect the generated FMU to work on a different system (The system would need a compatible Python version and libraries). But to ease its usage the wrapper is compile using the limited Python API. So the provided binary libraries for Linux and Windows 64-bits should be compatible with any Python 3 environment. If you need to compile the wrapper for a specific configuration, you will need CMake and a C++ compiler. The commands for building the wrapper on Linux and on Windows can be seen in the GitHub workflow.

PythonFMU does not automatically resolve 3rd party dependencies either. If your code includes e.g. numpy, the target system also needs to have numpy installed.

Would you rather build FMUs in Java? Check out FMI4j!
Need to distribute your FMUs? FMU-proxy to the rescue!

Credits

This works has been possible thanks to the contributions of @markaren from NTNU-IHB and @fcollonval from Safran SA.