ModelicaSystem cannot instantiate model, but sendExpression works

[cbu-hw]

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

[cbu-hw]

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

[AnHeuermann]

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

[AnHeuermann]

@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.

[cbu-hw]

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?

[cbu-hw]

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?

[arun3688]

@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")
>>>

[cbu-hw]

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? 🤷

[arun3688]

@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

[adeas31]

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

[cbu-hw]

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.

[adeas31]

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.