# Simulations
MIKE+Py allows you to execute simulations defined within your MIKE+ model directly from Python. This is primarily done using the [run()](../reference/Database.md#mikeplus.Database.run) method of an opened [Database](../reference/Database.md#mikeplus.Database) object.
# 
Running Simulations
The most straightforward way to run a simulation is by calling `db.run()` on your database object. By default, this executes the currently active simulation setup defined in the MIKE+ project.
``` python
# db is an opened mikeplus.Database object
result_files = db.run()
```
The [run()](../reference/Database.md#mikeplus.Database.run) method will pause your Python script (it's a blocking call) until the MIKE+ simulation engine has completed its execution.
# 
Specifying Simulation and Model
You can control which simulation to execute and which model engine to use:
- **Simulation Setup**: The `simulation_muid` parameter is the MUID of the simulation setup to run (e.g., "BaseRun", "Scenario_A_Sim"). If omitted, the active simulation in the model is used.
``` python
# Runs a specific simulation setup
results = db.run(simulation_muid="FloodEvent_2023_Sim")
```
- **Simulation Option**: The keyword-only `sim_option` parameter selects the engine: `"CS_MIKE_1D"` (rivers, collection systems and overland flow), `"CS_SWMM"`, `"WD_EPANET"` (water distribution), or `"CS_MIKE_1D_JobList"` (generates an LTS job list). If omitted, it is derived from `db.active_model`; that only works for the CS_MIKE1D, CS_SWMM and WD_EPANET models, and raises `ValueError` otherwise.
``` python
# Runs using the EPANET engine for water distribution
results = db.run(sim_option="WD_EPANET")
```
You can combine these parameters:
``` python
results = db.run(
simulation_muid="PeakDemand_Scenario",
sim_option="WD_EPANET"
)
```
# 
Simulation Output
When the engine finishes, `db.run()` returns a list of `pathlib.Path` objects: the result files the simulation setup is configured to write. They are not checked for existence, so a path may be missing if the simulation failed.
``` python
result_paths = db.run()
for path in result_paths:
print(f"Generated result file: {path}")
```
# 
Error Handling
`db.run()` raises `RuntimeError` if the engine fails to start, exits with an error, or doesn't write its result files; the message names the engine's logs. It raises `ValueError` if `sim_option` is invalid or cannot be derived from the active model, or if the model has no simulation with the given MUID.
``` python
try:
result_files = db.run()
except RuntimeError as e:
print(f"Simulation failed: {e}")
```
# 
Example
Here's a complete example of opening a database and running the active simulation:
``` python
import mikeplus as mp
with mp.open("path/to/your_model.sqlite") as db:
print(f"Active simulation: {db.active_simulation}")
print(f"Active model: {db.active_model}")
try:
results = db.run()
except RuntimeError as e:
print(f"Simulation failed: {e}")
else:
missing = [path for path in results if not path.exists()]
if missing:
print(f"Simulation did not produce: {missing}")
else:
print(f"Result files: {results}")
```