Method add

Lib/graphlib.py:59–84

Add a new node and its predecessors to the graph. Both the *node* and all elements in *predecessors* must be hashable. If called multiple times with the same node argument, the set of dependencies will be the union of all dependencies passed in. It is possible to a

(self, node, *predecessors)

        return result

    def add(self, node, *predecessors):
        """Add a new node and its predecessors to the graph.

        Both the *node* and all elements in *predecessors* must be hashable.

        If called multiple times with the same node argument, the set of dependencies
        will be the union of all dependencies passed in.

        It is possible to add a node with no dependencies (*predecessors* is not provided)
        as well as provide a dependency twice. If a node that has not been provided before
        is included among *predecessors* it will be automatically added to the graph with
        no predecessors of its own.

        Raises ValueError if called after "prepare".
        """
        if self._ready_nodes is not None:
            raise ValueError("Nodes cannot be added after a call to prepare()")

        # Create the node -> predecessor edges
        nodeinfo = self._get_nodeinfo(node)
        nodeinfo.npredecessors += len(predecessors)

        # Create the predecessor -> node edges
        for pred in predecessors:
            pred_info = self._get_nodeinfo(pred)
            pred_info.successors.append(node)

    def prepare(self):
        """Mark the graph as finished and check for cycles in the graph.