A fully working version of the scheduling language with added examples

transformation/schedule/schedule_lib/null_node.py

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+"""
+null_node.py
+
+Defines the NullNode class, a no-op singleton execution node used for open execution pins
+in the object diagram execution graph.
+"""
+
+from abc import ABC
+from typing import List, Type
+from jinja2 import Template
+from api.od import ODAPI
+from .funcs import generate_dot_node
+from .singleton import Singleton
+from .exec_node import ExecNode
+
+class NullNode(ExecNode, metaclass=Singleton):
+    """
+    A no-op execution node representing a null operation.
+
+    This node is typically used to represent a placeholder or open execution pin.
+    It always returns a fixed result and does not perform any operation.
+    """
+
+    def __init__(self):
+        """
+        Initializes the NullNode instance.
+        Inherits unique ID and state behavior from ExecNode.
+        """
+        super().__init__()
+
+    def execute(self, port: str, exec_id: int, od: ODAPI) -> tuple[int, any] | None:
+        """
+        Simulates execution by returning a static result indicating an open pin.
+
+        Args:
+            port (str): The name of the input port.
+            exec_id (int): The current execution ID.
+            od (ODAPI): The Object Diagram API instance providing execution context.
+
+        Returns:
+            tuple[int, str] | None: A tuple (-1, "open pin reached") indicating a no-op.
+        """
+        return -1, "open pin reached"
+
+    @staticmethod
+    def get_exec_output_gates():
+        """
+        Returns the list of output gates for execution.
+
+        Returns:
+            list: An empty list, as NullNode has no output gates.
+        """
+        return []
+
+    def generate_dot(
+        self, nodes: List[str], edges: List[str], visited: set[int], template: Template
+    ) -> None:
+        """
+        Generates DOT graph representation for this node if it hasn't been visited.
+
+        Args:
+            nodes (List[str]): A list to accumulate DOT node definitions.
+            edges (List[str]): A list to accumulate DOT edge definitions.
+            visited (set[int]): Set of already visited node IDs to avoid cycles.
+            template (Template): A Jinja2 template used to render the node's DOT representation.
+        """
+        if self.id in visited:
+            return
+        generate_dot_node(
+            self,
+            nodes,
+            template,
+            **{
+                "label": "null",
+                "ports_exec": (
+                    self.get_exec_input_gates(),
+                    self.get_exec_output_gates(),
+                ),
+            }
+        )