Adding field which, depending on direction field value, gets value from previous or next row/feature in another field?

Question

I am having difficulty getting to grips with arcpy and cursors. What i aim to do is the following: Depending on the direction specified in Test I wish to update the Target field. If it is forward, the Target should receive the Value of AP from the next row/feature. In this example for the first feature, the Target would be 2. Aditionally, if the direction specified is backward the Target field should receive the value from the previous row. To make matters worse, the AP and Target fields are strings (and converting them is not an option as the data provided in ususally alphanumeric), so simply adding and subtracting 1 is not possible.

what i have so far:

i = 0  
lastvalue = []  
with arcpy.da.SearchCursor(InFC, [Direction, AP]) as cursor:  
    for row in cursor:
        if Direction == "forward":
            newField = AP[row+1] ## here id like to reference the next value somehow
        else:
            newField = AP[row-1] ## here id like to reference the previous value

Answer 1

A cursor can only look at one row at a time but you can use two: Store all AP values in a list using a SearchCursor. Then use indexes to fetch values from the list and update using UpdateCursor. counter is keeping track of current row and used as index to fetch values from AP list. I dont know what you want to do at first/last row when you cant go backwards/forwards, im using current row value:

fc = 'contour'
fields = ['AP','Test','Target']

AP_list = [i[0] for i in arcpy.da.SearchCursor(fc, fields[0])]
listlength = len(AP_list)

counter = 0
with arcpy.da.UpdateCursor(fc, fields) as cursor:
    for row in cursor:
        if row[1] == 'forward':
            if counter == listlength-1:
                print 'Last row, cant go forward! Using current row value'
                value = 0                
            else:    
                value = 1
        else:
            if counter == 0:
                print 'First row, cant go back! Using current row value'
                value = 0
            else:
                value = -1
        row[2] = AP_list[counter+value]
        cursor.updateRow(row)
        counter+=1