Maya: Nondestructive holds

mnh.py

import pymel.core as pc
import pymel.core.animation as pca
import pymel.core.nodetypes as pcn
import maya.mel

# create animation layer
if pc.ls(selection=True):
    anim_layer = pca.animLayer(addSelectedObjects=True)
    pc.rename(anim_layer, 'baked_secondary_keys')
    anim_layer.override.set(True)
    anim_layer.mute.set(True)
else:
    pc.warning('No nodes selected!')

# get frame range
aPlayBackSliderPython = maya.mel.eval('$tmpVar=$gPlayBackSlider')
frame_range = None
if pc.timeControl(aPlayBackSliderPython, q=True, rangeVisible=True):
    frame_range = pc.timeControl(aPlayBackSliderPython, q=True, rangeArray=True)
else:
    frame_range = [pc.playbackOptions(animationStartTime=True, q=True),
                   pc.playbackOptions(animationEndTime=True, q=True)]

# storing current time for later
current_time = pca.currentTime(q=True)

# baking stepped keys on every second frame
for node in pc.ls(selection=True):
    for f in range(int(frame_range[0]), int(frame_range[1]), 2):
        pca.currentTime(f)
        pca.setKeyframe(node, inTangentType='linear', outTangentType='step', animLayer=anim_layer.name())

# animating weight on animation layer
if pc.ls(selection=True):

    pca.currentTime(frame_range[0]-1)
    anim_layer.weight.set(0)
    pca.setKeyframe(anim_layer, attribute='weight')
    
    pca.currentTime(frame_range[0])
    anim_layer.weight.set(1)
    pca.setKeyframe(anim_layer, attribute='weight')

    pca.currentTime(frame_range[1])
    anim_layer.weight.set(1)
    pca.setKeyframe(anim_layer, attribute='weight')
    
    pca.currentTime(frame_range[1] + 1)
    anim_layer.weight.set(0)
    pca.setKeyframe(anim_layer, attribute='weight')

#restoring current time
pca.currentTime(current_time)