Applying symbology to layers within the Table of Contents with Python

Question

I am using arcpy to pull in layers from a file geodatabase but I receive the following error below. How can I assign symbology from a .lyr file to a TOC layer using arcpy?

# Name: Create Map
# Purpose: Fixes bugs and other mapping problems 

# Import system modules
import arcpy
from arcpy import env

# Set the current workspace
env.workspace = "I:\UPDM.gdb"

# Rebuild Map Workspace
#
mxd = arcpy.mapping.MapDocument(r"C:\Users\aa2zz6\Desktop\test\Untitled.mxd")

df = arcpy.mapping.ListDataFrames(mxd, "*")[0]
# Add layer to TOC
#
addLayer = arcpy.mapping.Layer(r"I:\UPDM.gdb\P_PipeSystem\P_Meters")
arcpy.mapping.AddLayer(df, addLayer, "BOTTOM")

#Set layer to apply symbology to
inputLayers = ["P_Meters",]

# Set layer that output symbology will be based on
symbologyLayer = (r"C:\Temp\Meters.lyr")

# Apply the symbology from the symbology layer to the input layer
for layer in inputLayers:
arcpy.ApplySymbologyFromLayer_management (layer, symbologyLayer)

Error

Traceback (most recent call last):
File "C:\Users\aa2zz6\Downloads\CREATE NEW MXD.py", line 29, in <module>
arcpy.ApplySymbologyFromLayer_management (layer, symbologyLayer)
File "C:\Program Files (x86)\ArcGIS\Desktop10.6\ArcPy\arcpy\management.py", 
line 6934, in ApplySymbologyFromLayer
raise e
ExecuteError: Failed to execute. Parameters are not valid.
ERROR 000732: Input Layer: Dataset P_Meters does not exist or is not 
supported
Failed to execute (ApplySymbologyFromLayer).

Answer 1

Since this post was cross-posted I wanted to share the solution that solved this issue.

Credit: Randy Burton

Original Source: https://community.esri.com/thread/208705-apply-symbology-to-toc-layers

import os
import arcpy # if outside ArcMap

# inside ArcMap, use "CURRENT" for document name
mxd = arcpy.mapping.MapDocument(r"C:\Path\To\SymbolTest.mxd")
# layer file is in directory with mxd map document; this will be the 
workspace
arcpy.env.workspace = os.path.dirname(mxd.filePath)

# dictonary matches map layer with symbology layer file
# layer name in TOC : name of layer file (can use full path/file name if not in map directory)
symbols = {'SymbolTest':'LayerSymbology.lyr'}

for layer in arcpy.mapping.ListLayers(mxd):
    if layer.name in symbols:
    print "Layer: '{}' - previous symbology type: '{}'.".format(layer.name, layer.symbologyType)
    # http://desktop.arcgis.com/en/arcmap/latest/tools/data-management-toolbox/apply-symbology-from-layer.htm
    # ApplySymbologyFromLayer_management (in_layer, in_symbology_layer)
    print "Applying symbology to layer '{}' using '{}'.".format(layer.name, symbols[layer.name])
    arcpy.ApplySymbologyFromLayer_management(layer, symbols[layer.name])
    print "Layer: '{}' - new symbology type: '{}'.".format(layer.name, layer.symbologyType)
else:
print "Layer '{}' not updated.".format(layer.name)

# may need to refresh map
# arcpy.RefreshTOC()
# arcpy.RefreshActiveView()

del mxd