CODEWITHSUNDEEP
pythonregexmod-rewritetext-files
Dj_ 96
Dj_ 96

Reputation: 185

How to read and write a text file in the same time in python?

I am trying to open a text file, read it and after using a regex function to find which lines to edit, modify my text file. However what happens is that after finding the lines and edit them i can not write the modified Content in the text file again. 

remove_commas = re.compile("House")
answer = {}

global line1

with open("\DEMO_houses.txt", "r") as inp:

    for line in inp:
        if remove_commas.match(line):

            line1 = line.replace(',', '')
            print line1

with open("DEMO_houses.txt", "w") as document1:
        document1.write(line1)

What happens is that it just delets my text file, and writes only the first line modified.

Text file is something like this:

Street : Blue, Red
House: Big, enough
Garden : green, not green

And in the new text file i Need something like:

Street : Blue, Red
House: Big enough
Garden : green, not green

If anyone could help me I would really appreciate it. Thanks

Upvotes: 5

Views: 27751

Answers (2)

Aayush Mahajan
Aayush Mahajan

Reputation: 4033

What is happening in your code right now is that you first read all the lines in the with open("\DEMO_houses.txt", "r") as inp: block and then in the with open("DEMO_houses.txt", "w") as document1: block your code only writes back the last read line. Since write mode "w" erases the previous file, only the last line of your original file remains after your code finishes execution.

You might be better off first reading all the lines into memory, then mdifying those lines, and then writing them back into the same file like so:

import re

remove_commas = re.compile("House")

data = []
with open("DEMO_houses.txt", "r") as inp:  #Read phase
    data = inp.readlines()  #Reads all lines into data at the same time

for index, item in enumerate(data): #Modify phase, modification happens at once in memory
    if remove_commas.match(item):
        data[index] = item.replace(',', '')

with open("DEMO_houses.txt", "w") as document1: #write back phase
        document1.writelines(data)

Provided the file can be stored in memory without issues, this is a far superior method to reading and modifying the file one line at a time as modifications in memory are much faster, and the file in secondary storage would only be modified once.

Upvotes: 1

Sven Harris
Sven Harris

Reputation: 2939

You can try the following, the problem at the moment is that you are only storing and writing the final occurrence of the modified line, instead it's better to create a copy of the modified file in memory and then writing out (see below)

remove_commas = re.compile("House")
answer = {}

with open("\DEMO_houses.txt", "r") as inp:
    new_file_lines = []
    for line in inp:
        if remove_commas.match(line):
            line = line.replace(',', '')
        new_file_lines.append(line)

with open("DEMO_houses.txt", "w") as document1:
        document1.writelines(new_file_lines)

Upvotes: 3

Related Questions