insert_line_after_match

#!/usr/bin/env python

import re
import sys

line_pattern=sys.argv[1]
line_to_insert = sys.argv[2]

text = open( '/dev/stdin' ).read()
match_found = False
matches = re.finditer(line_pattern, text)

m = None      # optional statement. just for clarification
for m in matches:
    match_found = True
    pass       # just loop to the end


if (match_found):
    m.start()  # equals the starting index of the last match
    m.end()    # equals the ending index of the last match 

    # now you can do your substring of text to add whatever
    #   you wanted to add. For example,
print(text[0:m.end()] + "\n" + line_to_insert + text[(m.end()+1):])


#print(text)