fmuloader ⚙️

A lightweight, zero-dependency Python library for loading and calling FMI 2.0 and 3.0 shared-library binaries via ctypes.

Installation 📦

Add fmuloader to your project with uv:

uv add fmuloader

To install uv, see https://docs.astral.sh/uv/getting-started/installation/

How to use 🚀

FMI 2.0 Co-Simulation

from fmuloader.fmi2 import Fmi2Slave, Fmi2Type

slave = Fmi2Slave("model.fmu", model_identifier="MyModel")

slave.instantiate("instance1", Fmi2Type.CO_SIMULATION, guid="{...}")
slave.setup_experiment(start_time=0.0, stop_time=10.0)
slave.enter_initialization_mode()
slave.exit_initialization_mode()

t, dt = 0.0, 0.01
while t < 10.0:
    slave.do_step(t, dt)
    t += dt

values = slave.get_real([1, 2])
slave.terminate()
slave.free_instance()

FMI 3.0 Co-Simulation

from fmuloader.fmi3 import Fmi3Slave

slave = Fmi3Slave("model.fmu", model_identifier="MyModel")

slave.instantiate_co_simulation("instance1", instantiation_token="{...}")
slave.enter_initialization_mode(start_time=0.0, stop_time=10.0)
slave.exit_initialization_mode()

t, dt = 0.0, 0.01
while t < 10.0:
    result = slave.do_step(t, dt)
    t += dt

values = slave.get_float64([1, 2])
slave.terminate()
slave.free_instance()

FMI 3.0 Model Exchange

from fmuloader.fmi3 import Fmi3Slave

slave = Fmi3Slave("model.fmu", model_identifier="MyModel")

slave.instantiate_model_exchange("instance1", instantiation_token="{...}")
slave.enter_initialization_mode(start_time=0.0)
slave.exit_initialization_mode()

result = slave.update_discrete_states()
while result.discrete_states_need_update:
    result = slave.update_discrete_states()
slave.enter_continuous_time_mode()

nx = slave.get_number_of_continuous_states()
slave.set_time(0.0)
derivs = slave.get_continuous_state_derivatives(nx)

slave.terminate()
slave.free_instance()

FMI 3.0 Scheduled Execution

from fmuloader.fmi3 import Fmi3Slave

slave = Fmi3Slave("model.fmu", model_identifier="MyModel")

slave.instantiate_scheduled_execution("instance1", instantiation_token="{...}")
slave.enter_initialization_mode(start_time=0.0)
slave.exit_initialization_mode()

slave.activate_model_partition(clock_reference=1001, activation_time=0.0)

slave.terminate()
slave.free_instance()

Features ✨

• Load and call FMI 2.0 and 3.0 shared-library binaries via ctypes
• Full Co-Simulation, Model Exchange, and Scheduled Execution support
• All FMI 3.0 data types: Float32, Float64, Int8–Int64, UInt8–UInt64, Boolean, String, Binary, Clock
• FMU state management: get, set, serialize, and deserialize
• Directional and adjoint derivatives
• Clock interval and shift functions
• Context manager support for automatic cleanup
• Automatic platform detection (macOS, Linux, Windows; x86, x86_64, aarch64)

Design philosophy 💡

fmuloader intentionally separates binary loading from modelDescription.xml parsing.

Most FMI libraries tightly couple XML parsing with binary invocation, pulling in heavy dependencies and making it hard to use one without the other. fmuloader takes a different approach:

• fmuloader handles only the binary loading — extracting the shared library from an .fmu archive, binding every C function via ctypes, and exposing thin Python wrappers.
• modelDescription.xml parsing is left to the user or to a dedicated library like fmureader.

This means:

• Zero runtime dependencies — fmuloader uses only the Python standard library.
• Bring your own parser — use fmureader, FMPy, lxml, or anything else to read GUIDs, value references, and variable metadata. Then pass them straight to fmuloader.
• Minimal surface area — each module (fmi2, fmi3) is a single file you can vendor into your own project if needed.

# Example: combine fmureader (parsing) with fmuloader (execution)
import fmureader.fmi3 as reader
from fmuloader.fmi3 import Fmi3Slave

md = reader.read_model_description("model.fmu")

slave = Fmi3Slave("model.fmu", model_identifier=md.co_simulation.model_identifier)
slave.instantiate_co_simulation("inst", instantiation_token=md.instantiation_token)
# ... use md.model_variables to look up value references, then call slave.get_float64() etc.

Related projects 🔗

• fmureader — Lightweight Pydantic-based modelDescription.xml parser for FMI 2.0 and 3.0
• FMPy — Full-featured FMI library with simulation, GUI, and more

Licensing 📄

The code in this project is licensed under MIT license. See the LICENSE file for details.