<!-- GENERATED by tools/generators/examplesDocsEmitter.py from python/ - do not edit -->
(testmodels-systemcontainerlifetimetest)=
# systemContainerLifetimeTest.py

You can view and download this file on Github: [systemContainerLifetimeTest.py](https://github.com/jgerstmayr/EXUDYN/tree/master/python/TestModels/systemContainerLifetimeTest.py)

```{code-block} python
:linenos:

#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# This is an EXUDYN example
#
# Details:  A MainSystem keeps its SystemContainer alive, whether it came from SC.AddSystem() or from
#           SC.GetSystem(i) (#2851): a function that builds a model in a container of its own and returns
#           only the system leaves a system that works - before, the system of GetSystem pointed into a
#           container that had been deleted.
#
# Author:   Johannes Gerstmayr
# Date:     2026-10-05
#
# Copyright:This file is part of Exudyn. Exudyn is free software. You can redistribute it and/or modify it under the terms of the Exudyn license. See 'LICENSE.txt' for more details.
#
#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

import exudyn as exu
import gc
import weakref

testIsActive = exu.sys.get('testIsActive', False)

def BuildModel(useGetSystem):
    """a model in a container of its own; only the system and a weak reference to the container are returned"""
    SC = exu.SystemContainer()
    mbs = SC.AddSystem()
    mbs.CreateGround()
    mbs.CreateMassPoint(referencePosition=[1,0,0], mass=1, gravity=[0,-9.81,0])
    if useGetSystem:
        mbs = SC.GetSystem(0)
    return (mbs, weakref.ref(SC))

u = 0
for useGetSystem in [False, True]:
    (mbs, container) = BuildModel(useGetSystem)
    gc.collect()
    mbs.Assemble()
    simulationSettings = exu.SimulationSettings()
    simulationSettings.solution.file.write = False
    simulationSettings.timeIntegration.verboseMode = 0
    mbs.SolveDynamic(simulationSettings)
    alive = container() is not None
    exu.Print('GetSystem' if useGetSystem else 'AddSystem', ': container alive', alive, ', objects',
              mbs.systemData.NumberOfObjects())
    u += alive + mbs.systemData.NumberOfObjects() + mbs.systemData.GetODE2Coordinates()[1]

exu.Print('solution of systemContainerLifetimeTest=', u)

exu.sys['testResult'] = u
```