Add nested modello feature

examples/nested_geometry.py

@@ -0,0 +1,20 @@
+"""Example showing nested models.
+
+>>> box = Box("B", base={"a": 3, "b": 4}, height=12)
+>>> box.base.c
+5
+>>> box.diagonal
+13
+"""
+from modello import InstanceDummy, Modello
+from examples.geometry import RightAngleTriangle
+from sympy import sqrt
+
+
+class Box(Modello):
+    """Simple box using a RightAngleTriangle as the base."""
+
+    base = RightAngleTriangle
+    height = InstanceDummy("height", positive=True)
+    diagonal = sqrt(base.c ** 2 + height ** 2)
+

examples/nested_line.py

@@ -0,0 +1,23 @@
+"""Example demonstrating nested models with a Line composed of Points.
+
+>>> line = Line("L", start={"x": 0, "y": 0}, end={"x": 3, "y": 4})
+>>> line.length
+5
+"""
+from modello import InstanceDummy, Modello
+from sympy import sqrt
+
+
+class Point(Modello):
+    """Simple 2D point."""
+
+    x = InstanceDummy("x", real=True)
+    y = InstanceDummy("y", real=True)
+
+
+class Line(Modello):
+    """Line consisting of two points."""
+
+    start = Point
+    end = Point
+    length = sqrt((end.x - start.x) ** 2 + (end.y - start.y) ** 2)

examples/streaming.py

@@ -59,6 +59,24 @@ class DoubleDataEntryFlow(ScalableFlow):
     unit_output = Rational(8 * 260, 24 * 365) / entry_time / 2
 
 
+class EntrySystem(Modello):
+    """Simple system demonstrating nesting of flows.
+
+    >>> sys = EntrySystem(
+    ...     "SYS",
+    ...     flow={"input": 20, "entry_time": 5, "unit_cost": Rational(1, 10), "scale": 2},
+    ...     overhead=1,
+    ... )
+    >>> sys.total_cost
+    6/5
+    """
+
+    flow = SingleDataEntryFlow
+    overhead = InstanceDummy("overhead", positive=True, rational=True)
+    total_cost = flow.cost + overhead
+
+
+
 def test_simple_system():
     """The wheels on the bus go round and round."""
     channel_input_rates = {"foo": 12, "bar": 3}