python - Error while editing many CSV files

Question

I asked this question a few days ago because I needed help with editing some CSV files: Fix numbering on CSV files that have deleted lines. The people of Stack Overflow helped me out a great deal however I keep getting an error saying AttributeError: 'int' object has no attribute 'strip'. The problem is that all the information in my CSV files are not integers. Being the python newbie that I am, a few days of trying to fix it only made things worse. Here is what I have from my previous question that gives me the error:

import csv
import glob
import os 
import re 

numbered = re.compile(r'N\d+').match

for fn in fns:
     # open for counting
     reader = csv.reader(open(fn,"rb"))
     count = sum(1 for row in reader if row and not any(r.strip() == 'DIF' for r in     row) and numbered(row[0]))

 # reopen for filtering
 reader = csv.reader(open(fn,"rb"))

 with open (os.path.join('out', fn), 'wb') as f:
    counter = 0
    w = csv.writer(f)
    for row in reader:
        if row and 'Count' in row[0].strip():
            row = ['Count', count]
        if row and not any(r.strip() == 'DIF' for r in row): #remove DIF
            if numbered(row[0]):
                counter += 1
                row[0] = 'N%d' % counter
        w.writerow(row)

The code is essentially supposed to run through a bunch of CSV files and delete all the lines that have 'DIF' in them and fix the numbering due to deleted lines. Does anyone have any suggestions?