Python arcpy recursive function problems

I'm trying to implement an algorithm using values from an arcpy module. Here is my equation written into code. I need for the initial value of the variables St and Yt to start off at zero. After the first time running through the loop I need the previous values of Yt,Qt,and St to be used for the next calculation. I havn't been able to figure out how to get to this to work.

V=0.416395
Dt= 0.5560694202
cursor = arcpy.da.SearchCursor(shapefile,mathlist)
for row in cursor:
for i in range(1:len(mathlist))
Yt = min(Dt,St)
St = min(St+Qt-Yt,V)
Qt = .82 * row *row[i]

If you want those variables set to zero for each row in shapefile, your code should look like this:

V=0.416395
Dt= 0.5560694202
cursor = arcpy.da.SearchCursor(shapefile,mathlist)
for row in cursor:
St = 0
Yt = 0
Qt = 0
for i in range(1:len(mathlist))
Yt = min(Dt,St)
St = min(St+Qt-Yt,V)
Qt = .82 * row *row[i]

'Qt' also needs to be assigned a value before it can be used in an expression.