Python Forum

I'm having issues getting the results i'm looking for (obviously...) I am trying to read a text file, then parse it looking for a string, If it sees that string replace text on the NEXT line. This is what I have so far:

import fileinput
import sys

x = 0
value = "car"

with fileinput.input(files="testfile.txt") as file:
    for line in file:
        if x == 1:
            line = line.replace("car", "truck")
            sys.stdout.write(line)
            print("Triggered")
            x = 0
        if value in line:
            x = 1
            print("Activated")

fileinput.close()

My textfile has the following: (just as a test)

Output:
This is line 1
This is line 2
Check
Changes
apple
Apricot
grape
car
car 
truck

Am I going about this the wrong way or am I close just missing something?

do you actually want to insert a new line into the file?

right now, you read a line and if 'car' is in that line, you leave it alone, read the next line, which may or may not contain 'car', and replace 'car' if found in that line. The original line is not modified.
is this what you want to do?

If this is homework, could you just post the assignment?

(Aug-06-2018, 03:24 PM)Larz60+ Wrote: [ -> ]do you actually want to insert a new line into the file?

right now, you read a line and if 'car' is in that line, you leave it alone, read the next line, which may or may not contain 'car', and replace 'car' if found in that line. The original line is not modified.
is this what you want to do?

If this is homework, could you just post the assignment?

No homework sadly, just a personal project working with text files. Yes, you are correct. I will change it to append or replace after I have a better starter to work with. Right now I just need something to give me a base framework to work with.

Only append the next line, No additions to line numbers. I tried using the fileinput.lineno() function but i'm not getting any better results.

I'll try to describe a better situation. If the text file consist of the following:

Apple
Pear
Apple
Apple
Grape

Current code:

import fileinput
import sys

x = 0
y = 0
value = "Pear"

with fileinput.input(files="testfile.txt", backup="test.bak",inplace=1) as file:
    for line in file:
        print(line, end='')
        if value in line:
            y = file.lineno()+1
            print(y)
        if file.lineno() == y:
            print("Line:"+line, end='')
            line = line.replace("Apple", "Orange")
            sys.stdout.write(line)
            print("Triggered", end='')

fileinput.close()

I want to ONLY change the line followed by "Pear" instead of changing every line that has apple in it. Hope that clarifies a bit.

Thank you in advance

EDIT:
If I'm thinking correctly on this I just need a way to keep the lines of the file while its parsing through it. When I run that code it erases everything but the last line. If I can get past that then I think I should be close to what I need.

I got it. Of course it was right in front of me I just had to realize what it was doing. So instead of it only writing a line to the file if it saw the trigger. It writes to the file every time and only replaces what it writes if triggered. Took me a bit to finally realize this but hey, it works right?

For any future finders of this post this is the code I ended up with.

Python file:

import fileinput
import sys

x = 0
y = 0
value = "Pear"

with fileinput.input(files="testfile.txt", backup="test.bak", inplace=1) as file:
    for line in file:
        if value in line:
            y = file.filelineno()+1
        if (file.filelineno() == y) and ("Apple" in line):
            line = line.replace("Apple", "Orange")
        sys.stdout.write(line)

fileinput.close()

Testfile.txt:

Apple
Orange
Pear
Apple
Apple
Grape
Pear
Orange

Output:
Apple
Orange
Pear
Orange
Apple
Grape
Pear
Orange

here's how I would do it:

def replace_text(infile, outfile, replace_this, with_this):
    with open(infile, 'r') as f_in, open(outfile, 'w') as f_out:
        for line in f_in:
            if replace_this in line:
                line = line.replace(replace_this, with_this)
            f_out.write(line)

def testit():
    replace_text('testfile.txt', 'testfile_new.txt', 'Apple', 'Orange')


if __name__ == '__main__':
    testit()

testfile.txt:

Output:
Apple
Pear
Apple
Apple
Grape

testfile_new.txt

Output:
Orange
Pear
Orange
Orange
Grape