How to obtain substring of big string text in Python?

Question

I have the following format of text files, which are outputs of an API:

TASK [Do this]
OK: {
    "changed":false,
    "msg": "check ok"
}

TASK [Do that]
OK

TASK [Do x]
Fatal: "Error message x"

TASK [Do y]
OK

TASK [Do z]
Fatal: "Stopped because of previous error"

The amount of lines, or tasks before and after the "Fatal" error are random, and I am only interested in the "Error message x" part.

Code as of now:

url = # API URL 
r = request.get(url, verify=False, allow_redirects=True, headers=headers, timeout=10)
output = r.text

I tried using a combination of output.split("Fatal", 1)[1] but it seems to return list index out of range, while also messing up the text, adding a lot of \n.

Answer 1

You can use the re package to use a regular expression to search for the text you need. There are probably more optimal regex, but I wrote this one quickly using regex101.com: Fatal: "(.+)"

import re

s = '''TASK [Do this]
OK: {
    "changed":false,
    "msg": "check ok"
}

TASK [Do that]
OK

TASK [Do x]
Fatal: "Error message x"

TASK [Do y]
OK

TASK [Do z]
Fatal: "Stopped because of previous error"'''

errors = re.findall(r'Fatal: "(.+)"', s)

for x in errors:
    print(x)