simple file flow question with csv.reader

[Matt]

Hi All, 

I am trying to do a really simple file operation, yet, it befuddles me...

I have a few hundred .csv files, and to each file, I want to manipulate the data, then save back to the original file. The code below will open up the files, and do the proper manipulations-- but I can't seem to save the files after the manipulation.. 

How can I save the files-- or do I need to try something else maybe with split, join, etc..
 

import os
import csv
for filename in os.listdir("/home/matthew/Desktop/pero.ngs/blast"):
	with open(filename, 'rw') as f:
		reader = csv.reader(f)
		for row in reader:
			print ">",row[0],row[4],"\n",row[1], "\n", ">", row[2], "\n", row[3]



Thanks in advance, Matt