# Entropyk — Python Bindings

High-performance Python bindings for the [Entropyk](../../README.md) thermodynamic simulation library, built with [PyO3](https://pyo3.rs/) and [Maturin](https://www.maturin.rs/).

## Quickstart

### Installation (Development)

```bash
# From the bindings/python directory:
pip install maturin
maturin develop --release

# Verify installation:
python -c "import entropyk; print(entropyk.Pressure(bar=1.0))"
```

### Basic Usage

```python
import entropyk

# ── 1. Physical Types (type-safe units) ──

p = entropyk.Pressure(bar=12.0)
print(p.to_kpa())        # 1200.0 kPa
print(p.to_pascals())    # 1200000.0 Pa

t = entropyk.Temperature(celsius=45.0)
print(t.to_kelvin())     # 318.15 K

h = entropyk.Enthalpy(kj_per_kg=420.0)
m = entropyk.MassFlow(kg_per_s=0.05)

# Arithmetic
dp = entropyk.Pressure(bar=10.0) - entropyk.Pressure(bar=3.0)


# ── 2. Build a Refrigeration Cycle ──

system = entropyk.System()

comp = system.add_component(entropyk.Compressor(efficiency=0.85))
cond = system.add_component(entropyk.Condenser(ua=5000.0))
exv  = system.add_component(entropyk.ExpansionValve())
evap = system.add_component(entropyk.Evaporator(ua=3000.0))

system.add_edge(comp, cond)
system.add_edge(cond, exv)
system.add_edge(exv, evap)
system.add_edge(evap, comp)
system.finalize()


# ── 3. Solve ──

config = entropyk.FallbackConfig(
    newton=entropyk.NewtonConfig(max_iterations=200, tolerance=1e-6),
    picard=entropyk.PicardConfig(max_iterations=500, relaxation=0.5),
)

try:
    result = config.solve(system)
    print(f"Converged in {result.iterations} iterations")
    print(f"State: {result.state_vector}")
except entropyk.TimeoutError:
    print("Solver timed out")
except entropyk.SolverError as e:
    print(f"Solver failed: {e}")
```

## Recompiling after Rust Changes

Because the Python bindings rely on the Rust source code (`crates/components`, `crates/solver`, etc.), you **must recompile the Python package** if you modify the underlying Rust physics engine.

To recompile the bindings manually, simply use Maturin from the `bindings/python` directory with your virtual environment activated:

```bash
cd bindings/python
source .venv/bin/activate
maturin develop --release
```

*Note: If you added a new structural field in Rust (e.g. adding a `size` parameter to a Component struct), make sure to also update the Python wrapper class in `bindings/python/src/` so the macro `#[pyclass]` reflects the new shape before recompiling. You can use the `/update-python-bindings` agent workflow to do this automatically.*

## API Reference

### Physical Types

| Type | Constructors | Conversions |
|------|-------------|-------------|
| `Pressure` | `pa=`, `bar=`, `kpa=`, `psi=` | `to_pascals()`, `to_bar()`, `to_kpa()`, `to_psi()` |
| `Temperature` | `kelvin=`, `celsius=`, `fahrenheit=` | `to_kelvin()`, `to_celsius()`, `to_fahrenheit()` |
| `Enthalpy` | `j_per_kg=`, `kj_per_kg=` | `to_j_per_kg()`, `to_kj_per_kg()` |
| `MassFlow` | `kg_per_s=`, `g_per_s=` | `to_kg_per_s()`, `to_g_per_s()` |

All types support: `__repr__`, `__str__`, `__float__`, `__eq__`, `__add__`, `__sub__`

### Components

| Component | Constructor | Description |
|-----------|------------|-------------|
| `Compressor` | `(m1..m10, speed_rpm, displacement, efficiency, fluid)` | AHRI 540 performance model |
| `Condenser` | `(ua)` | Heat rejection coil |
| `Evaporator` | `(ua)` | Heat absorption coil |
| `Economizer` | `(ua)` | Internal heat exchanger |
| `ExpansionValve` | `(fluid, opening)` | Isenthalpic throttling |
| `Pipe` | `(length, diameter, fluid, density, viscosity, roughness)` | Darcy-Weisbach pressure drop |
| `Pump` | `(pressure_rise_pa, efficiency)` | Liquid pump |
| `Fan` | `(pressure_rise_pa, efficiency)` | Air fan |
| `FlowSplitter` | `(n_outlets)` | Flow distribution |
| `FlowMerger` | `(n_inlets)` | Flow recombination |
| `FlowSource` | `(pressure_pa, temperature_k)` | Boundary source |
| `FlowSink` | `()` | Boundary sink |

### Solver

```python
# Newton-Raphson (fast convergence)
config = entropyk.NewtonConfig(max_iterations=100, tolerance=1e-6, line_search=True)

# Picard / Sequential Substitution (more robust)
config = entropyk.PicardConfig(max_iterations=500, tolerance=1e-4, relaxation=0.5)

# Fallback (Newton → Picard on divergence)
config = entropyk.FallbackConfig(newton=newton_cfg, picard=picard_cfg)

result = config.solve(system)  # Returns ConvergedState
```

### Exceptions

```
EntropykError (base)
├── SolverError
│   ├── TimeoutError
│   └── ControlSaturationError
├── FluidError
├── ComponentError
├── TopologyError
└── ValidationError
```

## Running Tests

```bash
cd bindings/python
maturin develop
pytest tests/ -v
```

## Examples

- [`examples/simple_cycle.py`](examples/simple_cycle.py) — Build and solve a refrigeration cycle
- [`examples/migration_from_tespy.py`](examples/migration_from_tespy.py) — TESPy → Entropyk migration guide