Update Y axis expressions of a line chart based on multi select list box using IronPython

from Spotfire.Dxp.Data import *
from Spotfire.Dxp.Application.Visuals import *
from System.Collections.Generic import List
from Spotfire.Dxp.Data import DataPropertyClass
selection = Document.Data.Properties.GetProperty(DataPropertyClass.Document, "lbMetrics").Value
#print str(selection)[1:-1]
allMetrics = ['Presented' , 'Interested', 'Fulfilled', 'Total_Revenue', 'Take_Rate', 'VPM', 'AOV']

Presented = '''
	CASE  

	WHEN DocumentProperty("sRollingDaysTrend")=7 THEN 
	 Sum([Presented]) OVER (LastPeriods(7,[Create_Dt])) / DocumentProperty("sRollingDaysTrend")

	WHEN DocumentProperty("sRollingDaysTrend")=14 THEN 
	 Sum([Presented]) OVER (LastPeriods(14,[Create_Dt])) / DocumentProperty("sRollingDaysTrend")
	 
	WHEN DocumentProperty("sRollingDaysTrend")=30 THEN 
	 Sum([Presented]) OVER (LastPeriods(30,[Create_Dt])) / DocumentProperty("sRollingDaysTrend")
	 
	END As [Pres #]
'''


Interested = '''
	CASE  

	WHEN DocumentProperty("sRollingDaysTrend")=7 THEN 
	 Sum([Interested]) OVER (LastPeriods(7,[Create_Dt])) / DocumentProperty("sRollingDaysTrend")

	WHEN DocumentProperty("sRollingDaysTrend")=14 THEN 
	 Sum([Interested]) OVER (LastPeriods(14,[Create_Dt])) / DocumentProperty("sRollingDaysTrend")
	 
	WHEN DocumentProperty("sRollingDaysTrend")=30 THEN 
	 Sum([Interested]) OVER (LastPeriods(30,[Create_Dt])) / DocumentProperty("sRollingDaysTrend")
	 
	END As [Interested]
'''


str = ''
 
for s in selection:
	for a in allMetrics:
		if s==a:
			if len(str) == 0:
				str += eval(a)
			else:
				str += ',' + eval(a)
		else:
			pass

#print str
viz = viz.As[Visualization]()
viz.YAxis.Expression = ""

viz.YAxis.Expression = str
viz.YAxis.IndividualScaling = True
viz.YAxis.IndividualScalingMode = IndividualScalingMode.Color
viz.YAxis.Scale.ShowGridlines = True