Grouping values, creating a sum and writing to excel, Python

i am putting together a script to take some data from an access table and write it to an excel table. In the process, I'm trying to format the excal table. I have pasted the output of the excel table below my script.

In the following script, I pull the data from the access table and get it into the excel table. it groups all the values in the first column (i.e. all the M1's, all the M20a's, and so on). The second column is their associated area in hectares. The third column is the sum of the area for each grouped value.

All the sum of the areas are correct and in the right place, except the last group (ZWA). It's not writing the sum for that value. I have a feeling that I need to set the script so that it detects the last row in the table.

import arcpy, xlwt, sys, traceback, datetime
from arcpy import env
from xlwt import *
from itertools import groupby
from collections import defaultdict
from time import strftime


# Set workspace for the file to be used
env.workspace = "Z:\TestFolder"
env.overwriteOutput = True


# Stores access table into a variable and sorts the SMU field ascendingly
cur = arcpy.SearchCursor("Access Table", "", "", "SMU", "SMU A")

# Create excel workbook
book = Workbook()
sheet1 = book.ad开发者_如何转开发d_sheet('Sheet 1')

# Create a dictionary
col_counts = defaultdict(int)

# Set a varialb eto be used in looping through rwos and detecting when the value in the cell is different from the last
last_value = object()

# Set the start of 2 counters. rowx is to count rows in the access table. rowadd is to add the values in a field alled row.SHAPE_Area
rowx = 3
rowadd = 0

# Loop through the access table
for row in cur:

    # Ask if the current value is not equal to the last value in the row.SMU column
    if row.SMU != last_value:

        last_value = row.SMU

        # if the current value doesn't equal the last value, then place the sum of the row.SHAPE_Area field for the last value in a new cell in a different column.
        sheet1.write(int(rowx+1),3,rowadd/10000)

        # Reset counter to 0
        rowadd = 0
        # Add 2 to the counter to create a space between groups of values in the excel table
        rowx += 2
    else:
        # Else only add 1 to the counter if the value in the cell reamisn the same as the last one
        rowx += 1


    # if the value of the row is the same as the last one, then add the values for a second column together and write to the excel sheet
    if row.SMU == str(last_value):

        rowadd += row.SHAPE_Area
        print rowadd

        sheet1.write(int(rowx),0,row.SMU)
        sheet1.write(int(rowx),1,row.SHAPE_Area/10000)

# Set the counter to += the last value in the (col_counts[last_value]) variable and start over again
rowx += (col_counts[last_value])

# Save the workbook
book.save("Z:\TestFolder\simple.xls")

Below is the output table in excel. See that I am not getting the ZWA total area in the third column. Can anyone suggest why this is? I'd like to get rid of the 0 in the first row of the third column as well.

                      0
M1      0.076492721     
M1      0.406600839     
M1      2.98016238      
                      3.46325594
M20a    0.665489193     
                      0.665489193
M21     0.005333282     
                      0.005333282
M23b    0.190245719     
M23b    0.233315779     
                      0.423561498
S1      0.201021287     
S1      0.176390376     
S1      0.200409435     
S1      0.009312814     
S1      0.071782163     
                      0.658916076
ZWA     0.387293182     

You need something like the (untested) code below.

import arcpy, xlwt, sys, traceback, datetime
from arcpy import env
#### from xlwt import *
#### (a) horrid, you need only 1 class (b) you already imported xlwt
### from itertools import groupby
#### good idea, but get some simple programming skills first
#### from collections import defaultdict #### why?
from time import strftime

# Set workspace for the file to be used
env.workspace = "Z:\TestFolder"
env.overwriteOutput = True

# Stores access table into a variable and sorts the SMU field ascendingly
cur = arcpy.SearchCursor("Access Table", "", "", "SMU", "SMU A")

# Create excel workbook
book = Workbook()
sheet1 = book.add_sheet('Sheet 1')

# Create a dictionary #### what for?
col_counts = defaultdict(int)

# Set a varialb eto be used in looping through rwos
# and detecting when the value in the cell is different from the last
previous = dummy = object()

# Set the start of 2 counters.
# rowx is to count rows in the excel table, NOT the access table
# rowadd is to add the values in a field alled row.SHAPE_Area
rowx = 3
rowadd = 0
# Loop through the access table
for row in cur:
    if row.SMU != previous != dummy:
        # if the current value doesn't equal the previous value,
        # AND it's not the first row, then place
        # the sum of the row.SHAPE_Area field for the previous value
        # in a new cell in a different column.
        rowx += 1 # start a new output row
        sheet1.write(rowx, 3, rowadd/10000)
        # Reset counter to 0
        rowadd = 0
    rowx += 1 # start a new output row
    rowadd += row.SHAPE_Area
    print rowadd
    sheet1.write(rowx, 0, row.SMU)
    sheet1.write(rowx, 1, row.SHAPE_Area/10000)
    previous = row.SMU

# End of input. Write the final subtotal (unless there was no input)
if previous != dummy:
    rowx += 1
    sheet1.write(rowx, 3, rowadd/10000)

##### What is the purpose of this???    
# Set the counter to += the last value in the
# (col_counts[previous]) variable and start over again
rowx += (col_counts[previous])

# Save the workbook
book.save(r"Z:\TestFolder\simple.xls")