Gaffer: trying to add the ability to modify the graph on dispatch

on_dispatch.py

import os

import Gaffer
import GafferDispatch


# Add an 'onDispatch' task input to all task nodes.

tasknode_init_orig = GafferDispatch.TaskNode.__init__

def tasknode_init(self, *args, **kwargs):
    result = tasknode_init_orig(self, *args, **kwargs)
    if 'onDispatch' not in self:
        plug = GafferDispatch.TaskNode.TaskPlug('onDispatch', flags=Gaffer.Plug.Flags.Default | Gaffer.Plug.Flags.Dynamic)
        self.addChild(plug)
        Gaffer.Metadata.registerValue(plug, 'description', 'Task to execute before the graph is "locked" by the dispatcher.')
        Gaffer.Metadata.registerValue(plug, 'nodule:type', 'GafferUI::StandardNodule')
        Gaffer.Metadata.registerValue(plug, 'noduleLayout:section', 'left')
        Gaffer.Metadata.registerValue(plug, 'plugValueWidget:type', '')
    return result

GafferDispatch.TaskNode.__init__ = tasknode_init


# Check for anything connected to 'onDispatch' on the dispatched nodes.

def dispatch_signal(dispatcher, nodes):
    sub_nodes = []
    for node in nodes:
        plug = node['onDispatch'].getInput()
        if plug:
            sub_nodes.append(plug.node())
    if sub_nodes:
        name = 'onDispatch_' + dispatcher.getName()
        sub_dispatcher = GafferDispatch.LocalDispatcher(name)
        sub_dispatcher['jobsDirectory'].setValue(os.path.join(dispatcher.jobDirectory(), os.path.pardir, os.path.pardir, name))
        sub_dispatcher.dispatch(sub_nodes)

GafferDispatch.Dispatcher.dispatchSignal().connect(dispatch_signal, scoped=False)