edit text files/ add lines if missing (regex)

[wardancer84]

i am trying to layout some code to edit aix stanza files. basically i want to add/remove/edit special formated config values from various text files. in the end this should come out as an working ansible module ;-).

this is the desired format:

stanza1:
        value1 = attr1
        value2 = attr2

stanza2:
        value1 = attr1
        value3 = attr1

stanza3:
        value1 = attr1
        value1 = attr1

i want to search for the stanza and only add it if it does not exists. a newline is needed above each stanza to separate it from the above. the value/attr pairs should have a "tab' in front of them. it should be possibe to remove/add value/attr pairs to stanzas and removal of the whole stanza (incl. related value/attrs).

i already experimented with regexes but the follwing leaves the file empty.

#!/usr/bin/env python

import re


with open('stanza_test', 'r+') as fh:
    text = fh.read()
    if re.search(r'(?m)^shittyjohn:', text):
        print('Found.')
    else:
        print('Not found.')
        pattern = r'^((?:[^\n]+\n){%d})'
        fh.seek(0)
        fh.write(
            re.sub(pattern, r'\1shittyjohn:\n', text)
        )

any hints,food for thought,ideas, code snippets would be of great help, as i am little bit stuck with this.