Question

I need to to a RegEx search and replace of all commas found inside of quote blocks.
i.e.

"thing1,blah","thing2,blah","thing3,blah",thing4  

needs to become

"thing1\,blah","thing2\,blah","thing3\,blah",thing4  

my code:

inFile  = open(inFileName,'r')
inFileRl = inFile.readlines()
inFile.close()

p = re.compile(r'["]([^"]*)["]')
for line in inFileRl:
    pg = p.search(line)
    # found comment block
    if pg:
        q  = re.compile(r'[^\\],')
        # found comma within comment block
        qg = q.search(pg.group(0))
        if qg:
            # Here I want to reconstitute the line and print it with the replaced text
            #print re.sub(r'([^\\])\,',r'\1\,',pg.group(0))

I need to filter only the columns I want based on a RegEx, filter further,
then do the RegEx replace, then reconstitute the line back.

How can I do this in Python?

Answer 1

The csv module is perfect for parsing data like this as csv.reader in the default dialect ignores quoted commas. csv.writer reinserts the quotes due to the presence of commas. I used StringIO to give a file like interface to a string.

import csv
import StringIO

s = '''"thing1,blah","thing2,blah","thing3,blah"
"thing4,blah","thing5,blah","thing6,blah"'''
source = StringIO.StringIO(s)
dest = StringIO.StringIO()
rdr = csv.reader(source)
wtr = csv.writer(dest)
for row in rdr:
    wtr.writerow([item.replace('\\,',',').replace(',','\\,') for item in row])
print dest.getvalue()

result:

"thing1\,blah","thing2\,blah","thing3\,blah"
"thing4\,blah","thing5\,blah","thing6\,blah"