More Pythonic way to loop through UpdateCursor?

Question

I have several sets of fields to populate based on other fields. The code below works, but I am wondering if there is a more Pythonic way to march through the i,j pairs? (Actual fieldnames are not this simple.)

i = ['FieldA1', 'FieldB1', 'FieldC1', 'FieldD1']
j = ['FieldA2', 'FieldB2', 'FieldC2', 'FieldD2']

if len(i) != len(j):
    arcpy.AddMessage("Error - i & j are not the same length")
    sys.exit()

for n in range(len(i)):
    fields = [i[n], j[n]]
    with arcpy.da.UpdateCursor(mySHP, fields) as cursor:
        for row in cursor:
            val = row[0]
            if float(val) == -999:
                row[1] = -999
            else:
                row[1] = float(val) / 100
            cursor.updateRow(row)

Answer 1

Since you have working code I think that this is a question that would be more on-topic at the Code Review Stack Exchange than here. However, the inclusion of ArcPy cursors may confuse that site so in this instance I will provide an answer.

I suspect that this code:

i = ['FieldA1', 'FieldB1', 'FieldC1', 'FieldD1']
j = ['FieldA2', 'FieldB2', 'FieldC2', 'FieldD2']
fields = i + j
halfNumFields = len(i)
with arcpy.da.UpdateCursor(mySHP, fields) as cursor:
    for row in cursor:
        for n in range(halfNumFields):
            if int(row[n]) == -999:
                row[n + halfNumFields] = -999
            else:
                row[n + halfNumFields] = float(row[n]) / 100
            cursor.updateRow(row)

would run faster than yours:

i = ['FieldA1', 'FieldB1', 'FieldC1', 'FieldD1']
j = ['FieldA2', 'FieldB2', 'FieldC2', 'FieldD2']

for n in range(len(i)):
    fields = [i[n], j[n]]
    with arcpy.da.UpdateCursor(mySHP, fields) as cursor:
        for row in cursor:
            val = row[0]
            if float(val) == -999:
                row[1] = -999
            else:
                row[1] = float(val) / 100
            cursor.updateRow(row)

Irrespective of whether it is more Pythonic or not, the way that I would become sure about whether it runs faster is by performance timing the two alternatives.