Write docs for system API module

src/ifcopenshell-python/ifcopenshell/api/system/disconnect_port.py

@@ -21,13 +21,51 @@ import ifcopenshell.api
 
 
 class Usecase:
-    def __init__(self, file, **settings):
+    def __init__(self, file, port=None):
+        """Disconnects a port from any other port
+
+        A port may only be connected to one other port, so the other port is not
+        needed to be specified.
+
+        :param port: The IfcDistributionPort to disconnect.
+        :type port: ifcopenshell.entity_instance.entity_instance
+        :return: None
+        :rtype: None
+
+        Example::
+
+            # A completely empty distribution system
+            system = ifcopenshell.api.run("system.add_system", model)
+
+            # Create a duct and a 90 degree bend fitting
+            duct = ifcopenshell.api.run("root.create_entity", model,
+                ifc_class="IfcDuctSegment", predefined_type="RIGIDSEGMENT")
+            fitting = ifcopenshell.api.run("root.create_entity", model,
+                ifc_class="IfcDuctFitting", predefined_type="BEND")
+
+            # The duct and fitting is part of the system
+            ifcopenshell.api.run("system.assign_system", model, product=duct, system=system)
+            ifcopenshell.api.run("system.assign_system", model, product=fitting, system=system)
+
+            # Create 2 ports, one for either end of both the duct and fitting.
+            duct_port1 = ifcopenshell.api.run("system.add_port", model, element=duct)
+            duct_port2 = ifcopenshell.api.run("system.add_port", model, element=duct)
+            fitting_port1 = ifcopenshell.api.run("system.add_port", model, element=duct)
+            fitting_port2 = ifcopenshell.api.run("system.add_port", model, element=duct)
+
+            # Connect the duct and fitting together. At this point, we have not
+            # yet determined the direction of the flow, so we leave direction as
+            # NOTDEFINED.
+            ifcopenshell.api.run("system.connect_port", model, port1=duct_port2, port2=fitting_port1)
+
+            # Disconnect the port. note we could've equally disconnected
+            # fitting_port1 instead of duct_port2
+            ifcopenshell.api.run("system.disconnect_port", model, port=duct_port2)
+        """
         self.file = file
         self.settings = {
-            "port": None,
+            "port": port,
         }
-        for key, value in settings.items():
-            self.settings[key] = value
 
     def execute(self):
         rels = self.settings["port"].ConnectedTo or []