[Tutor] modify csv textfile

[TGW]

I have a pipe delimited text file with 5 columns which looks like this:
12345|some text|some more text|example125 oo3 3456|example32423
11223|more text|and more|example/73d 77665|example455667
12677|text|more|anotherexample 123|anotherexample45

What I want to output is:
12345|some text|some more text|example|example32423
11223|more text|and more|example|example455667
...
12677|text|more|anotherexample 123|anotherexample45

So column 4 is where the change occurs, but only if the beginning of the string in column 4  =~ /^example/i  # and it should be case insensitive

#!/usr/bin/env python
import csv
import re

filename = raw_input("Enter the filename to edit: ")

reader = csv.reader(open(filename, 'rb'), delimiter='|', quoting=csv.QUOTE_NONE)
for row in reader:
    print row

....
I can print the file, I just need a little help searching and replacing the column 4 data element.

Thanks