refactor_mirror.py

def applyBtnCmd(self, *args):
	# Grab and check info from UI lists and scroll areas.
	attributes_to_mirror_list    = self.driverScroll.getSelectItem()
	driven_object_attribute_list = self.objAttrScroll.getSelectItem()
	
	if len(attributes_to_mirror_list) < 1:
		cmds.warning( 'No attribute to mirror selected' )	
		return False
	
	if len(driven_object_attribute_list) < 1:
		cmds.warning( 'No driven attribute selected' )
		return False
	
	# Organize the data from the UI as necesssary
	attrToMirror = attributes_to_mirror_list[0]
	driver = cmds.textField(self.driverTxt, query = True, tx = True)
	driven = cmds.textField(self.drivenTxt, query = True, tx = True)
	drivenObjs = self.objScroll.getSelectItem()
	drivenAttr = driven_object_attribute_list[0]
	
	# EC NOTE: What if the user has no object selected?
	if not drivenObjs:
		cmds.warning( 'No driven objs selected' )		
		return False
	
	# EC NOTE: Try to avoid try/except whenever possible. Bad python practice.
	# EC NOTE:Strip your functionality from your interface so other tools can access this functionality without having to have the UI filled
	# out/button clicks etc.
	
	# Do the stuff now.
	result, message = process_mirror_sdk( attrToMirror, driver, driven, driven_objs=drivenObjs, drivenAttr = drivenAttr )
	
	if not result:
		cmds.warning( message )
	return True
	
	
def process_mirror_sdk( attr_to_mirror, driver, driven, driven_objs = None, drivenAttr = None ):
	# Store existing animation curves
	animCurves = cmds.listConnections(
      driver + '.{}'.format(attrToMirror),
      source=False,
      destination=True,
      type="animCurveUA"
   )
	if not animCurves:
		# Early exit.	
		return False, 'Driver attribute has no connections'
	
	for curve in animCurves:
		curve_destination = pm.listConnections(curve, d=True, s=False, scn=True)
		if pm.objectType(curve_destination[0], isType='blendWeighted'):
			curve_destination = pm.listConnections(curve_destination, d=True, s=False, scn=True)

		crvDest_parentCnt = getNumberOfParents(curve_destination)

		for obj in drivenObjs:
			drivenObj = pm.ls(obj)
			drivenObj_parentCnt = getNumberOfParents(drivenObj)

			# Instead of just having a conditional that skips the rest of the loop implicity, call it out so the reader is aware.
			if drivenObj_parentCnt != crvDest_parentCnt:
				continue
			
			# Duplicate animation curve
			dupCurve = cmds.duplicate(curve)
			
			# Output driven obj's attr into the dup curve's input
			cmds.connectAttr((driven + '.{}'.format(attrToMirror)), (dupCurve[0] + '.input'))
			
			# The attribute to output the curve into
			destination_attr = obj + ".{}".format(drivenAttr)

			# Check to see if target object already has an incoming connection in given attribute.
			# If so, a blendWeighted node has to be created
			if cmds.connectionInfo(destination_attr, isDestination=True):
				create_blend_weighted_node( dupCurve, destination_attr )

				# Output BlendWeighted to target object
				cmds.connectAttr(blend_weighted + ".output", destination_attr)

			else:
				cmds.connectAttr(dupCurve[0] + '.output', destination_attr)
	
	return True, 'Success!'


def create_blend_weighted_node( dupCurve, destination_attr ):
	existing_curves = cmds.listConnections(
      destination_attr,
      source = True,
      destination = False
   )
	blend_weighted = cmds.createNode(
      "blendWeighted",
      n = destination_attr + "_BLEND",
      ss = True
   )
	for i in range(len(existing_curves)):
		# Break connection b/w existing curve output and destination attr
		cmds.disconnectAttr((existing_curves[i] + ".output"), destination_attr)
		# Input existing curve output into blendWeighted
		cmds.connectAttr((existing_curves[i] + ".output"), blend_weighted + ".input[{}]".format(i))
		# Input dup curve into blendWeighted
		cmds.connectAttr(dupCurve[0] + '.output', blend_weighted + ".input[{}]".format(i + 1))
	
	return blend_weighted


def getNumberOfParents( obj ):
	# Why is this method part of your class? it doesn't rely on any persistant logic.
	parentsList = obj[0].getAllParents()
	if parentsList:
		return len(parentsList)
	else:
		return 0