Calc Geom tool | Python Fiddle

import arcpy

class Toolbox(object):
    def __init__(self):
        """Define the toolbox (the name of the toolbox is the name of the
        .pyt file)."""
        self.label = "CalcGeom"
        self.alias = "RBNPythonToolBox"

# List of tool classes associated with this toolbox
        self.tools = [Tool1]

class Tool1(object):
    def __init__(self):
        """Define the tool (tool name is the name of the class)."""
        self.label = "CalcGeom"
        self.description = "Tool to calculate geometry"
        self.canRunInBackground = True

def getParameterInfo(self):
        # First parameter
    	in_features = arcpy.Parameter(
            displayName="Input Features",
            name="in_features",
            datatype="Feature Layer",
            parameterType="Required",
            direction="Input")
   	in_features.filter.list = ["Point", "Polyline", "Polygon"]

# Second parameter
        field = arcpy.Parameter(
            displayName="Field Name",
            name="field_name",
            datatype="Field",
            parameterType="Required",
            direction="Input")

field.parameterDependencies = [in_features.name]
        field.filter.list = ["Short","Long","Double","Float","Text"]

# Third parameter
        geomProperty = arcpy.Parameter(
            displayName="Property",
            name="geomProperty",
            datatype="String",
            parameterType="Required",
            direction="input")

# Fourth parameter
        units = arcpy.Parameter(
           displayName="Units",
           name="units",
           datatype="String",
           parameterType="Optional",
           direction="input",
           enabled=False)

# Fifth parameter
        out_features = arcpy.Parameter(
           displayName="Output Features",
           name="out_features",
           datatype="Feature Layer",
           parameterType="Derived",
           direction="output")

out_features.parameterDependencies = [in_features.name]
        out_features.schema.clone = True

params = [in_features, field, geomProperty, units, out_features]
        return params

def isLicensed(self):
        """Set whether tool is licensed to execute."""
        return True

def updateParameters(self, parameters):
        #Get Inputs
        in_features = parameters[0]
        geomProperty = parameters[2]
        units = parameters[3]

#Geometry Property Filter Lists
	pointPropertyList   = ['X Coordiante of Point',
			       'Y Coordinate of Point']
	linePropertyList    = ['Length', 'X Coordinat of Line Start',
                               'Y Coordinate of Line Start',
                               'X Coordinate of line End',
                               'Y Coordinate of Line End']
	polygonPropertyList = ['Area', 'Perimeter',
                               'X Coordinate of Centroid',
                               'Y Coordinate of Centroid']
	#Get shape type of input to determine
	#filter list for geometry property parameter
	if in_features.value:
  	    desc = arcpy.Describe(in_features.valueAsText)
	    if desc.shapeType == 'Point':
                geomProperty.filter.list = pointPropertyList
            elif desc.shapeType == 'Polyline':
                geomProperty.filter.list = linePropertyList
            elif desc.shapeType == 'Polygon':
                geomProperty.filter.list = polygonPropertyList

#Unit Filter List
	areaUnitList        = ['Acres', 'Ares', 'Hectares',
                               'Square Centimeters', 'Square Inches',
			       'Square Feet', 'Square Kilometers',
                               'Square Meters', 'Square Miles',
                               'Square Millimeters', 'Square Yards',
                               'Square Decimeters']
	lengthUnitList      = ['Centimeters', 'Feet', 'Inches',
                               'Kilometers', 'Meters', 'Miles',
                               'Yards', 'Decimal Degrees']
	#Get geometry property input to determine filter list for unit parameter
	if geomProperty.value:
            if geomProperty.valueAsText == 'Area':
                units.enabled = True
                units.filter.list = areaUnitList
            elif geomProperty.valueAsText in ['Length', 'Perimeter']:
                units.enabled = True
                units.filter.list = lengthUnitList
            else:
                units.value = ""
                units.filter.list = []
                units.enabled = False
	return

def updateMessages(self, parameters):
        in_features = parameters [0]
	geomProperty = parameters[2]
	units = parameters[3]

#Check if input is Multipoint or Multipatch and if so set an error
	if in_features.value:
            desc = arcpy.Describe(in_features.valueAsText)
            if desc.shapeType in ['Multipoint', 'Multipatch']:
                in_features.setErrorMessage(
                    "{0} features are not supported.".format(desc.shapeType))

#Check if certain geometry property value is set with no units and add
	if geomProperty.valueAsText in ['Length', 'Perimeter', 'Area']:
            if not units.value:
                units.setErrorMessage(
                    "Units required for {0} property".format(geomProperty.valueAsText))
	return

def execute(self, parameters, messages):
        #Get Inputs
	in_features = parameters[0].valueAsText
	field = parameters[1].valueAsText
	geomProperty = parameters[2].valueAsText
	units = parameters[3].valueAsText

shapeFieldName = arcpy.Describe(in_features).shapeFieldName

#Create the expression
	exp = "!" + shapeFieldName
	if geomProperty == "Area":
            exp += ".area@" + units.replace(' ', '')
	elif geomProperty in ['Length', 'Perimeter']:
            exp += ".length@" + units.replace(' ', '')
	else:
            propertyList = geomProperty.split(' ')
            coord = propertyList[0]
            if propertyList[-1] in ['Point','Start']:
                exp += ".firstPoint." + coord
            elif propertyList[-1] == 'End':
                exp += ".lastPoint." + coord
            elif propertyList[-1] == 'Centroid':
                exp += ".centroid." + coord
	exp += "!"

messages.addMessage(
            "\nExpression used for field calculation: {0}\n".format(exp))

#Calculate Field
	arcpy.CalculateField_management(in_features, field,
                                        exp, "Python_9.3")
        return

def isLicensed(self):
        """Set whether tool is licensed to execute."""
        return True

def updateParameters(self, parameters):
        #Get Inputs
        in_features = parameters[0]
        geomProperty = parameters[2]
        units = parameters[3]

#Unit Filter List
	areaUnitList        = ['Acres', 'Ares', 'Hectares',
                               'Square Centimeters', 'Square Inches',
			       'Square Feet', 'Square Kilometers',
                               'Square Meters', 'Square Miles',
                               'Square Millimeters', 'Square Yards',
                               'Square Decimeters']
	#Get geometry property input to determine filter list for unit parameter
	if geomProperty.value:
            if geomProperty.valueAsText == 'Area':
                units.enabled = True
                units.filter.list = areaUnitList
            elif geomProperty.valueAsText in ['Length', 'Perimeter']:
                units.enabled = True
                units.filter.list = lengthUnitList
            else:
                units.value = ""
                units.filter.list = []
                units.enabled = False
	return

def updateMessages(self, parameters):
        in_features = parameters [0]
	geomProperty = parameters[2]
	units = parameters[3]

shapeFieldName = arcpy.Describe(in_features).shapeFieldName

messages.addMessage(
            "\nExpression used for field calculation: {0}\n".format(exp))

#Calculate Field
	arcpy.CalculateField_management(in_features, field,
                                        exp, "Python_9.3")
        return

Python Fiddle

Python Cloud IDE