Given the attached test.csv file, the following program
loops forever (can't even ^c):

import re

orig = open('test.csv')

file_contents = orig.read()
orig.close()

find_line = re.compile(r'^(".*")?(,(".*")?)*\n')
search_result = find_line.search(file_contents)
print search_result.span()

The corresponding tcl program works correctly:

set orig [open test.csv r]

set file_contents [read $orig]
close $orig

regexp -indices {^(".*")?(,(".*")?)*\n} $file_contents
\ indices
puts "Indices were $indices"

Both tests were run on a TP G41 running Gentoo Linux.

Logged In: YES 
user_id=1474165

If you eliminate the \n at the end of the regular
expression, the python program works correctly (for this
example; I am trying to use regular expressions to parse the
.csv files generated by Microsoft Outlook, which contain
eols inside fields, so I'm trying to find the eols *not*
inside fields with this regexp, so I need the \n; I'll have
to go to Plan B, I suppose).

You're being a victim of two issues here:

1.regular expression matching can take a long time. see:
http://bugs.python.org/issue1662581

2. regular expression matching was not interruptible:
http://bugs.python.org/issue846388

Duplicate and partly fixed

This problem has been addressed in issue #2636.

Although the extra checks certainly aren't foolproof, some regular
expressions which were slow won't be any more.