> import linecache
> file_path = r'D:\work\python\test.txt'
> line_number = 5
> def get_line_context(file_path, line_number):
...  return linecache.getline(file_path, line_number).strip()
...
> get_line_context(file_path, line_number)
'This is line 5.'
>

import os 
file = open( "a.txt", "r" ) 
file_add = open("a.txt","r") 
content = file.read() 
content_add = file_add.read() 
pos = content.find( "buildTypes")
if pos != -1: 
  content = content[:pos] + content_add + content[pos:] 
  file = open( "a.txt", "w" ) 
  file.write( content ) 
  file.close() 
  file_add.close()