 Here is a basic example of how you might set up a simulation using dd4hep in Python. Please note that this is a simplified version and you may need to adjust it according to your specific needs.

```python
import argparse
from dd4hep.core.logger import logger
from dd4hep.configuration import build_app, build_setup
from dd4hep.detector.hepmc import HepMCWriter
from dd4hep.visualization.gui import GUI
from dd4hep.simulation.framework import Simulation
from dd4hep.simulation.components import Tracker, ParticleGun
from dd4hep.simulation.actions import EventAction, TrackingAction
from dd4hep.utils.filesystem import load_xml

def run_simulation(args):
    # Load constants
    constants = load_xml(args.geometry)

    # Set up Geant4
    geom = build_setup(constants)

    # Print detectors
    print(geom.topDetector().name())

    # Configure UI, tracking field, and event actions
    app = build_app()
    app.ui().setVisible(args.gui)
    app.field().setVisible(False)

    # Set up particle gun and tracker
    gun = ParticleGun(ParticleGun.eplus)
    tracker = Tracker()

    # Configure event actions
    actions = [
        EventAction(),
        TrackingAction(tracker),
        HepMCWriter()
    ]

    # Build physics list and execute Geant4
    sim = Simulation(geom, actions)
    sim.execute(gun, 1000)

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Run a dd4hep simulation.")
    parser.add_argument("--geometry", type=str, help="Geometry file")
    parser.add_argument("--gui", action="store_true", help="Show GUI")
    args = parser.parse_args()
    run_simulation(args)
```

This script sets up a basic simulation with a particle gun, a tracker, and a HepMC writer for output. It also includes options for a geometry file and a GUI. The `run_simulation` function is called if the script is run as the main program.