CODEWITHSUNDEEP
pythonfileio
nandi1596
nandi1596

Reputation: 69

How do I replace the a specific first character of lines with something else in multiple .txt files? (Python)

So basically I have .txt files in this sort of form

0 45 56 67 89
1 45 56 33 21

Some .txt files might also be blank. Some may contain one or more lines. Now I want to replace all the 1 in the first character of lines to 0. Everything else remains same. So the above .txt example should look like

0 45 56 67 89
0 45 56 33 21

I tried two ways One way was :

import glob
import os
source="path of my folder/"
for filename in glob.glob(os.path.join(source, '*.txt')):
    with open(os.path.join(os.getcwd(), filename), "r+") as f:
        lines = f.readlines()
for filename in glob.glob(os.path.join(source, '*.txt')):
    with open(os.path.join(os.getcwd(), filename), "w+") as f:
        for line in lines:
            if line[0]=='1':
                line[0].replace('1','0')

But this just removes all lines, regardless of whether it starts with 0 or 1

I have tried this:

source="path/ of my folder which has the files/"
for root, dirs, filenames in os.walk(source):
    for f in filenames:
        this_file = open(os.path.join(source, f), "r")
        this_files_data = this_file.readlines()
        this_file.close()
# rewrite the file with all line except the one you don't want
        this_file = open(os.path.join(source, f), "w")
        for line in this_files_data:
            if line[0] in "1":
                line[0].replace("0","1")
                this_file.write(line)
        this_file.close()

But this just removes all lines starting with 0 and keeps the ones with 1.

Upvotes: 1

Views: 823

Answers (1)

Barmar
Barmar

Reputation: 781096

You should use just one loop. Read each file, make the changes you want, then rewrite the file.

You can use a regular expression to replace 1 at the start of each line.

import re
import glob
import os

for filename in glob.glob(os.path.join(source, '*.txt')):
    with open(filename, "r") as f:
        contents = f.read()
    contents = re.sub(r'^1', '0', contents, flags = re.MULTILINE)
    with open(filename, "w") as f:
        f.write(contents)

You shouldn't use os.path.join(getcwd(), filename). The files are in the source directory, not the current directory, and glob.glob() returns those pathnames.

Upvotes: 1

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