What's the real error message? I can guess that it's a Type Error, but one thing is certain: There is no syntax error in that sample you posted. The Type Error what you'll get if that re.search() call doesn't find a match. The result on no match is None and you get a TypeError exception when you try to index that with [] brackets.
Also, your regular expression
"csrf_token":"(.*?)"
is suspect, since a ? (indicating 0 or 1 occurrences of the previous item) is meaningless after an * (meaning 0 or more occurrences). If it does match anything, it will match all of the .text field starting from the first occurrence of
''"csrf_token":"(.*?)"'
. That can't be what you want. (If it was, you didn't need a regular expression.)
After you fix your regular expression, you can sensibly avoid the type error with something like:
m = re.search("'"csrf_token":"([^"]*)"', response.text)
if m != None:
s.headers.update({'X-CSRFToken' : m.group(1));
That has two more guesses in it: First, that you want the match to include just one ("") quoted field immediately after a "csrf_token": match. That's why I used '[^"]' to match any character EXCEPT a quote, instead of '.'. Then, I guessed that you only wanted the quoted text to be included in your HTTP header. I don't do enough web work to know if that makes sense or not. Someone else might be able to help with that if you posted exactly what you want to accomplish.