ModelicaSystem cannot instantiate model, but sendExpression works

I am encountering puzzling behaviour trying to instantiate a simple model that is located at some path (not the current directory), which gets me an exception with exit status 3221225781 (google suggests this is "dll not found") in check_model_executable:

model MyModel
equation
end MyModel;

from OMPython import ModelicaSystem, OMCSessionZMQ
import sys
print(f'{sys.path=}')

print("works")
omc = OMCSessionZMQ()
print(omc.sendExpression("getVersion()"))
omc.sendExpression('loadFile("C:\\Users\\myuser\\Software_local\\Modelica\\Issues\\MyModel.mo")')
omc.sendExpression("instantiateModel(MyModel)")

print("broken")
model = ModelicaSystem(
    fileName='C:\\Users\\myuser\\Software_local\\Modelica\\Issues\\MyModel.mo',
    modelName='MyModel',
)

Output:

> python .\load_package.py
sys.path=['C:\\Users\\myuser\\Software_local\\Modelica\\Issues\\dll_find_problems', 'C:\\Users\\myuser\\AppData\\Local\\miniforge3\\envs\\modelica\\python312.zip', 'C:\\Users\\myuser\\AppData\\Local\\miniforge3\\envs\\modelica\\DLLs', 'C:\\Users\\myuser\\AppData\\Local\\miniforge3\\envs\\modelica\\Lib', 'C:\\Users\\myuser\\AppData\\Local\\miniforge3\\envs\\modelica', 'C:\\Users\\myuser\\AppData\\Local\\miniforge3\\envs\\modelica\\Lib\\site-packages', 'C:\\Users\\myuser\\AppData\\Local\\miniforge3\\envs\\modelica\\Lib\\site-packages\\win32', 'C:\\Users\\myuser\\AppData\\Local\\miniforge3\\envs\\modelica\\Lib\\site-packages\\win32\\lib', 'C:\\Users\\myuser\\AppData\\Local\\miniforge3\\envs\\modelica\\Lib\\site-packages\\Pythonwin']
works
C:\Users\myuser\Software_local\Modelica\Issues\dll_find_problems\load_package.py:6: DeprecationWarning: The class OMCSessionZMQ is depreciated and will be removed in future versions! Please use OMCSession* classes instead!
  omc = OMCSessionZMQ()
v1.28.0-dev.836+gca0c61d2c7.cmake
[OMC log for 'sendExpression(expr=loadFile("C:\Users\myuser\Software_local\Modelica\Issues\MyModel.mo"), parsed=True)']: [syntax:warning:2] Lexer treating \ as \\, since \U is not a valid Modelica escape sequence.
[OMC log for 'sendExpression(expr=loadFile("C:\Users\myuser\Software_local\Modelica\Issues\MyModel.mo"), parsed=True)']: [syntax:warning:2] Lexer treating \ as \\, since \u is not a valid Modelica escape sequence.
[OMC log for 'sendExpression(expr=loadFile("C:\Users\myuser\Software_local\Modelica\Issues\MyModel.mo"), parsed=True)']: [syntax:warning:2] Lexer treating \ as \\, since \S is not a valid Modelica escape sequence.
[OMC log for 'sendExpression(expr=loadFile("C:\Users\myuser\Software_local\Modelica\Issues\MyModel.mo"), parsed=True)']: [syntax:warning:2] Lexer treating \ as \\, since \M is not a valid Modelica escape sequence.
[OMC log for 'sendExpression(expr=loadFile("C:\Users\myuser\Software_local\Modelica\Issues\MyModel.mo"), parsed=True)']: [syntax:warning:2] Lexer treating \ as \\, since \I is not a valid Modelica escape sequence.
[OMC log for 'sendExpression(expr=loadFile("C:\Users\myuser\Software_local\Modelica\Issues\MyModel.mo"), parsed=True)']: [syntax:warning:2] Lexer treating \ as \\, since \M is not a valid Modelica escape sequence.
broken
Traceback (most recent call last):
  File "C:\Users\myuser\AppData\Local\miniforge3\envs\modelica\Lib\site-packages\OMPython\model_execution.py", line 80, in run
    cmdres = subprocess.run(
             ^^^^^^^^^^^^^^^
  File "C:\Users\myuser\AppData\Local\miniforge3\envs\modelica\Lib\subprocess.py", line 571, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['C:/Users/myuser/AppData/Local/Temp/b956fe61-9405-4aa1-b400-649fe415d817/MyModel.exe', '-help=help']' returned non-zero exit status 3221225781.

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Users\myuser\AppData\Local\miniforge3\envs\modelica\Lib\site-packages\OMPython\modelica_system_abc.py", line 205, in check_model_executable
    returncode = cmd_definition.run()
                 ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\myuser\AppData\Local\miniforge3\envs\modelica\Lib\site-packages\OMPython\model_execution.py", line 101, in run
    raise ModelExecutionException(f"Error running model executable {repr(cmdl)}: {ex}") from ex
OMPython.model_execution.ModelExecutionException: Error running model executable ['C:/Users/myuser/AppData/Local/Temp/b956fe61-9405-4aa1-b400-649fe415d817/MyModel.exe', '-help=help']: Command '['C:/Users/myuser/AppData/Local/Temp/b956fe61-9405-4aa1-b400-649fe415d817/MyModel.exe', '-help=help']' returned non-zero exit status 3221225781.

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Users\myuser\Software_local\Modelica\Issues\dll_find_problems\load_package.py", line 12, in <module>
    model = ModelicaSystem(
            ^^^^^^^^^^^^^^^
  File "C:\Users\myuser\AppData\Local\miniforge3\envs\modelica\Lib\site-packages\OMPython\compatibility_v400.py", line 35, in __init__
    super().__init__(*args, **kwargs)
  File "C:\Users\myuser\AppData\Local\miniforge3\envs\modelica\Lib\site-packages\OMPython\ModelicaSystem.py", line 68, in __init__
    self.model(
  File "C:\Users\myuser\AppData\Local\miniforge3\envs\modelica\Lib\site-packages\OMPython\modelica_system_omc.py", line 157, in model
    self.buildModel(variable_filter)
  File "C:\Users\myuser\AppData\Local\miniforge3\envs\modelica\Lib\site-packages\OMPython\modelica_system_omc.py", line 218, in buildModel
    self.check_model_executable()
  File "C:\Users\myuser\AppData\Local\miniforge3\envs\modelica\Lib\site-packages\OMPython\modelica_system_abc.py", line 207, in check_model_executable
    raise ModelicaSystemError(f"Cannot execute model: {exc}") from exc
OMPython.modelica_system_abc.ModelicaSystemError: Cannot execute model: Error running model executable ['C:/Users/myuser/AppData/Local/Temp/b956fe61-9405-4aa1-b400-649fe415d817/MyModel.exe', '-help=help']: Command '['C:/Users/myuser/AppData/Local/Temp/b956fe61-9405-4aa1-b400-649fe415d817/MyModel.exe', '-help=help']' returned non-zero exit status 3221225781.

I expect that this instantiation with ModelicaSystem works.
By the way, OMPython should really define a __version__ attribute so that one can easily report its version.

I suspect some path/environment problems, so I printed the PATH that Python sees. Please advise what I can do to add more diagnostics on the OMPython side.
The MyModel.bat content in the temporary directory is

@echo off
SET PATH=;C:/OpenModelica1.28.0-dev-64bit/bin/;C:/OpenModelica1.28.0-dev-64bit/lib/x86_64-windows-gnu/omc;%PATH%;
SET ERRORLEVEL=
CALL "%CD%/MyModel.exe" %*
SET RESULT=%ERRORLEVEL%

EXIT /b %RESULT%

Version and OS

Python Version 3.12.13 (via conda)
OMPython Version 4.1.0
OpenModelica Version v1.28.0-dev.836+gca0c61d2c7.cmake
OS: Windows 11

because dlls are not being found, possibly related OpenModelica/OpenModelica#16846?

Yes, same issue. Fixing it now. I guess the new installer is online in around 2 hours.

@arun3688

@arun3688 the installer now installs static libraries into lib/x86_64-windows-gnu/omc. You might need to check if that directory is already on the search path. But they should be hardcoded in the executables, so probably this will work out of the box.

It would be appreciated if the error could inform about which libraries are missing. I don't know if that's technically possible? I was under the assumption that for some reason it's shared libraries that are missing, not static ones, apparently that's wrong?

Yes, same issue. Fixing it now. I guess the new installer is online in around 2 hours.

Where will that be available in 2 hrs? Nightly installers are normally appearing during the night, no?

@cbu-hw

@cbu-hw i think the above issue might not be related to dll missing error i guess because that is related to github actions in the OpenModelicaSetuo, but this PR https://github.com/OpenModelica/OMPython/pull/476 should fix your issue i guess , i tested your model and it worked for me. we need to wait for the github action to pass

(base) c:\OPENMODELICAGIT\OpenModelica\OMPython>python
Python 3.13.5 | packaged by Anaconda, Inc. | (main, Jun 12 2025, 16:37:03) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from OMPython import ModelicaSystem
>>> mod = ModelicaSystem("C:/OPENMODELICAGIT/OMEditDir/mymodel/MyModel.mo", "MyModel")
>>>

this PR https://github.com/OpenModelica/OMPython/pull/476 should fix your issue i guess ,

Why do you think that? #476 is about directory-based packages, but my MWE is a single-file model? 🤷

@cbu-hw

@cbu-hw i tested your model in my computer and it worked, i am not using the latest nightly builds, so that is why it worked i guess

ModelicaSystem simulates the model as well so if you try to simulate the model via sendExpression then it will fail as well.

ModelicaSystem simulates the model as well so if you try to simulate the model via sendExpression then it will fail as well.

I cannot confirm that, it does not fail. Adding a line of print(omc.sendExpression("simulate(MyModel, stopTime=3.0)")) to the sendexpression section works as expected.

ModelicaSystem simulates the model as well so if you try to simulate the model via sendExpression then it will fail as well.

I cannot confirm that, it does not fail. Adding a line of print(omc.sendExpression("simulate(MyModel, stopTime=3.0)")) to the sendexpression section works as expected.

OK. We moved around binaries and we need to set PATH for running simulation via ModelicaSystem. I will push in a fix for it.

Yes, same issue. Fixing it now. I guess the new installer is online in around 2 hours.

Where will that be available in 2 hrs? Nightly installers are normally appearing during the night, no?

It seems today's nightly did not run sucessfully, the Windows nightly is still from yesterday morning, so I can't test if Andreas' fix resolved the problem.

Yes, we had some issues with signing release executable. We are working on it.

I just installed 1.28.0-dev.857+g5fee2cdbad.cmake that landed today, but that one seems to be just broken 🤷

Using v1.28.0-dev-429-g1819321c0f-cmake from late August, I don't get the exception, and simulation completes orderly AFAICT. So this is confirmed to be a regression now.

@AnHeuermann

That is a known issue. @AnHeuermann is working on it. We will let you know once a working nightly is available.

The installer dev-861 should now be updated and online.

@cbu-hw

@cbu-hw to my surprise even the windows test passed in #476

This issue still persists on my local machine. Can you test again and see if it works for you.

This issue still persists on my local machine. Can you test again and see if it works for you.

I still observe the crash with v1.28.0-dev.861+gec7b922228.cmake

Also let me remark that OpenModelica/OpenModelica#5809 would be very appreciated. Losing ~1h+ of productivity to switch from a working OM version to a fresh nightly as asked, then back to the working one to be able to continue to work is...frustrating and approaches being prohibitive.

I'd offer to git bisect on an OM source build (in a devcontainer) to find what introduced the problem, but there's a similar story here -- a fresh compilation takes ~hours, incremental ones I don't know yet, as the current master does not even Configure successfully on my machine.🤷 (edit: Ah I see now that that CMake kit is actually not supported)

I still observe the crash with v1.28.0-dev.861+gec7b922228.cmake

Should work fine with OpenModelica/OpenModelica#16870

I still observe the crash with v1.28.0-dev.861+gec7b922228.cmake

Should work fine with OpenModelica/OpenModelica#16870

We'll see. I'm not sure if that will work, AFAICT as detailed above the .bat file already has the correct paths (so I don't know what the tweaks in OpenModelica/OpenModelica#16870 should improve there), but for some reason ModelicaSystem does not seem to observe that?

No, there were some paths missing in the .bat file e.g., the C compiler path. OpenModelica/OpenModelica#16870 sets that.

With v1.28.0-dev.1026+gb748b1d61d.cmake I don't get the crash with exit status 3221225781 anymore.
However, now it crashes with exit status 1

OMPython.modelica_system_abc.ModelicaSystemError: Cannot execute model: Error running model executable ['C:/Users/myuser/AppData/Local/Temp/4e088cf1-03f0-42e5-9f76-2fd38c279baf/MyModel.exe', '-help=help']: Command '['C:/Users/myuser/AppData/Local/Temp/4e088cf1-03f0-42e5-9f76-2fd38c279baf/MyModel.exe', '-help=help']' returned non-zero exit status 1.

Running .\MyModel.bat -help=help, which should be equivalent to running the exe + path setting gives

LOG_STDOUT | error | -help: not implemented by this runtime

which is not surfaced by ModelicaSystem, but might be the reason behind the non-zero exit status.

Curiously enough, the (powershell) $LastExitCode of that call is 0 -- make of that what you will 🤪

This should work now as expected.

There were issues with simulation command line arguments when we switched from C to Rust runtime. Just update your OM.

Confirmed fixed with v1.28.0-dev.1157, thank you!

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ModelicaSystem cannot instantiate model, but sendExpression works #478

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ModelicaSystem cannot instantiate model, but sendExpression works #478

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cbu-hw commented on Sep 22, 2026

AnHeuermann commented on Sep 22, 2026

AnHeuermann commented on Sep 22, 2026

cbu-hw commented on Sep 22, 2026

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arun3688 commented on Sep 22, 2026

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cbu-hw commented on Sep 23, 2026

adeas31 commented on Sep 23, 2026

cbu-hw commented on Sep 23, 2026

cbu-hw commented on Sep 23, 2026

adeas31 commented on Sep 23, 2026

AnHeuermann commented on Sep 23, 2026

adeas31 commented on Sep 23, 2026

cbu-hw commented on Sep 24, 2026

adeas31 commented on Sep 24, 2026

cbu-hw commented on Sep 25, 2026

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cbu-hw commented on Sep 28, 2026

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cbu-hw commented on Oct 2, 2026

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