Maya scene modification aware via Pyblish

plugins.py

"""Implement scene modification awareness

By tracking Maya's undo queue, if there are any undo command that is not
a simple select after collecting completed, consider this scene has been
modified and require to reset Pyblish.

"""

import collections
import maya.OpenMaya as om
import pyblish.api


class AvalonSceneReady(pyblish.api.ContextPlugin):
    """Define current scene in ready state

    Collecte current undo count for later validation.

    """

    order = pyblish.api.CollectorOrder + 0.49999
    label = "Scene Ready"
    hosts = ["maya"]

    def process(self, context):
        from maya import cmds

        # Ensure undo queue is active
        cmds.undoInfo(state=True)

        with OutputDeque() as undo_list:
            cmds.undoInfo(query=True, printQueue=True)

        context.data["_undoCount"] = len(undo_list)


class AvalonCheckSceneReady(pyblish.api.ContextPlugin):
    """Validate current scene still fit the definition of *ready*

    By checking new undo commands in undo queue after collecting, and consider
    scene is not ready if there are any non-select command.

    """

    order = pyblish.api.ValidatorOrder - 0.49998
    label = "Is Scene Ready"
    hosts = ["maya"]

    def process(self, context):
        from maya import cmds

        if not cmds.undoInfo(query=True, state=True):
            raise Exception("Undo queue is not open, please reset.")

        undo_count = context.data["_undoCount"]
        # self.log.debug(undo_count)

        with OutputDeque(format=lambda l: l.split(": ", 1)[-1].strip(),
                         skip=undo_count,
                         ) as undo_list:
            cmds.undoInfo(query=True, printQueue=True)

        while undo_list:
            history = undo_list.pop()
            # self.log.debug(history)

            if history.startswith("select"):
                continue

            raise Exception("Scene has been modified, no longer in *ready* "
                            "state. Please reset.")


class OutputDeque(collections.deque):
    """Record Maya command output during the context

    A context manager, subclass of `collections.deque`.
    Maya command output will be added into this deque during the context.

    Args:
        ignore_empty (bool, optional): Whether to ignore empty formatted
            output line. Default True.
        format (callable, optional): Function for formatting output.
        skip (int, optional): Skip first numbers of outputs.
        max (int, optional): Max length of the deque.

    """

    def __init__(self,
                 ignore_empty=True,
                 format=None,
                 skip=0,
                 max=None):
        self.ignore_empty = ignore_empty
        self.format = format or (lambda line: line)
        self.skip = skip

        self.__callback_id = None
        self.__count = 0
        super(OutputDeque, self).__init__(maxlen=max)

    def __enter__(self):
        add_callback = om.MCommandMessage.addCommandOutputCallback

        def catch_output(msg, *args):
            self.__count += 1
            if self.__count <= self.skip:
                return

            formatted = self.format(msg)
            if formatted or not self.ignore_empty:
                self.append(formatted)

        self.__callback_id = add_callback(catch_output)

        return self

    def __exit__(self, *args):
        om.MCommandMessage.removeCallback(self.__callback_id)