Insert text into a text file following specific text using Python

Question

I have to edit some text files to include new information, but I will need to insert that information at specific locations in the file based on the surrounding text.

Th

Answer 1

This will look for any string, in the file (not specific, to be at the start of the line only, i.e. can exist spread over multiple lines as well).

Typically you can follow the algo as:

1. lookup for the string in the file, and capture "location"
2. then split the file about this "location", and attempt to create new files as
   • write start-to-loc content to new file
   • next, write your "NEW TEXT" to the new file
   • next, loc-to-end content to new file

Let us see code:

#!/usr/bin/python

import os

SEARCH_WORD = 'search_text_here'
file_name = 'sample.txt'
add_text = 'my_new_text_here'

final_loc=-1
with open(file_name, 'rb') as file:
        fsize =  os.path.getsize(file_name)
        bsize = fsize
        word_len = len(SEARCH_WORD)
        while True:
                found = 0
                pr = file.read(bsize)
                pf = pr.find(SEARCH_WORD)
                if pf > -1:
                        found = 1
                        pos_dec = file.tell() - (bsize - pf)
                        file.seek(pos_dec + word_len)
                        bsize = fsize - file.tell()
                if file.tell() < fsize:
                                seek = file.tell() - word_len + 1
                                file.seek(seek)
                                if 1==found:
                                        final_loc = seek
                                        print "loc: "+str(final_loc)
                else:
                                break

# create file with doxygen comments
f_old = open(file_name,'r+')
f_new = open("new.txt", "w")
f_old.seek(0)
fStr = str(f_old.read())
f_new.write(fStr[:final_loc-1]);
f_new.write(add_text);
f_new.write(fStr[final_loc-1:])
f_new.close()
f_old.close()