Maya force an attribute value during context, even for referenced, locked and animated attributes

maya_force_temporary_value.py

from maya import cmds
import maya.api.OpenMaya as om
import contextlib


def pairwise(iterable):
    """s -> (s0,s1), (s2,s3), (s4, s5), ..."""
    a = iter(iterable)
    return zip(a, a)


def get_plug(attr):
    sel = om.MSelectionList()
    sel.add(attr)
    plug = sel.getPlug(0)
    return plug
    
    
@contextlib.contextmanager
def ignore_reference_edits(ref_node):
    """During context do not register any reference edits to this reference node"""
    sel = om.MSelectionList()
    sel.add(ref_node)
    obj = sel.getDependNode(0)
    fn_ref = om.MFnReference(obj)
    original = fn_ref.ignoreReferenceEdits()
    try:
        fn_ref.setIgnoreReferenceEdits(True)
        yield
    finally:
        fn_ref.setIgnoreReferenceEdits(original)

    

@contextlib.contextmanager
def no_inputs(plug):
    connections = cmds.listConnections(plug,
                                       source=True,
                                       destination=False,
                                       plugs=True,
                                       connections=True) or []
    if not connections:
        # Do nothing if no inputs
        yield
        return
        
    try:
        for dest, src in pairwise(connections):
            cmds.disconnectAttr(src, dest, nextAvailable=False)
        yield
    finally:
        for dest, src in pairwise(connections):
            cmds.connectAttr(src, dest, force=True, nextAvailable=False)


@contextlib.contextmanager
def force_unlock(attr):
    """Unlock attribute via API during context.
    
    This also works for referenced nodes.
    """
    plug = get_plug(attr)
    original = plug.isLocked
    try:
        plug.isLocked = False
        yield
    finally:
        plug.isLocked = original
    

@contextlib.contextmanager
def attr_free_to_change(attr, disable_reference_edits=True):
    """Make attribute free to change during context.
    
    This unlocks the attribute and breaks incoming connections.
    After the context the lock state is reverted and any connections
    are reconnected.
    
    It's up to the user to make sure that at the end of the context
    the attribute does not have any animations or connections, otherwise
    the attribute is not ensured to revert correctly.

    """
    with contextlib.ExitStack() as stack:
        # Make sure any connect/disconnect does not get marked as reference
        # edit. Note that during the context this also means that any changes
        # during the context are not registered as reference edits either!
        if disable_reference_edits and cmds.referenceQuery(attr, isNodeReferenced=True):
            ref_node = cmds.referenceQuery(attr, referenceNode=True)
            stack.enter_context(ignore_reference_edits(ref_node))
        
        stack.enter_context(force_unlock(attr))
        stack.enter_context(no_inputs(attr))
        yield

            
    

camera = "cameraShape1"
plug = f"{camera}.overscan"

with attr_free_to_change(plug):
    value = cmds.getAttr(plug)
    try:
        
        cmds.setAttr(plug, 1.0)
        
        # Now camera overscan is 1.0 - even if the attribute had incoming connections
        # or was locked originally. After the context, it's reverted. This allows us
        # to now FORCE a playblast e.g. to be at overscan 1.0 but leave the user's scene
        # in tact afterwards
        print(cmds.getAttr(plug))
        cmds.currentTime(cmds.currentTime(q=True) + 1)
        print(cmds.getAttr(plug))
        
    finally:
        cmds.setAttr(plug, value)