Python Replace string in certain line

Question

In txt file projections.txt like this

0001|AA|17.12.2017.|20:30|21:00|ponedeljak|For a few dolars more|150|true
0002|BB|19.12.2017.|19:30|21:15|sreda|March on the Drina|300|true
0003|GG|20.12.2017.|18:00|19:00|cetvrtak|A fistful of Dolars|500|true
0004|GG|21.12.2017.|21:15|00:00|petak|The Good, the Bad and the Ugly|350|true

How to change string "true" with "false" (delete) in certain line. For example, if I input 0002, how to change in 2nd line. I tried something like this, but it's not working...

def delete_projection():
    with open('projections.txt') as projections:
    #projections = open('users.txt', 'r').readlines()
        delete = input("Input projection code you want to delete: ")
        for i in projections:
            projection = i.strip("\n").split("|")
            if delete == projection[0]:
                projection[8]="false"
                #projections.close()
    with open('projections.txt', 'w+') as projections:
        projections.write("false")
        projections.close()

you have to read the file as csv, modify & write the full file. There's no such thing as read/write on a text file.* — Jean-François Fabre
– Jean-François Fabre ♦, Commented Jan 31, 2018 at 15:20

Jean-François Fabre · Accepted Answer · 2018-01-31 15:43:35Z

1

your attempt makes no sense. When you're modifying your lines, the modification is lost.

And writing a text file in read/write cannot work. Writing false somewhere in the file cannot work either...

My proposal:

use csv module to handle the splitting
read the rows as a list of rows
store the rows with the modification
overwrite the file with the new data

like this:

import csv

def delete_projection():
    with open('projections.txt') as projections:
    #projections = open('users.txt', 'r').readlines()
        delete = input("Input projection code you want to delete: ")
        contents = []
        cr = csv.reader(projections,delimiter="|")
        for row in cr:
            if delete == row[0]:
                row[8]="false"
            contents.append(row)

    with open('projections.txt', 'w',newline="") as projections:
        cw = csv.writer(projections,delimiter="|")
        cw.writerows(contents)

edited Jan 31, 2018 at 15:43

answered Jan 31, 2018 at 15:26

Jean-François Fabre♦

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2 Comments

erhesto Over a year ago

Keeping whole file content in memory could be troublesome.

Neo Cortex Over a year ago

It works. Just change 'users.txt' to 'projections.txt'. I edited it to.

Ajax1234 · Accepted Answer · 2018-01-31 15:28:30Z

You can use re:

import re
s = """
0001|AA|17.12.2017.|20:30|21:00|ponedeljak|For a few dolars more|150|true
0002|BB|19.12.2017.|19:30|21:15|sreda|March on the Drina|300|true
0003|GG|20.12.2017.|18:00|19:00|cetvrtak|A fistful of Dolars|500|true
0004|GG|21.12.2017.|21:15|00:00|petak|The Good, the Bad and the Ugly|350|true
""" 
vals = re.findall('(?<=\n)\d+(?=\|)|(?<=^)\d+(?=\|)', s)
statements = re.findall('true|false', s)
new_s = re.sub('true|false', '{}', s)
to_change = '0002'
s = new_s.format(*[('true' if a == 'false' else 'false') if b == to_change else a for a, b in zip(statements, vals)])

Output:

0001|AA|17.12.2017.|20:30|21:00|ponedeljak|For a few dolars more|150|true
0002|BB|19.12.2017.|19:30|21:15|sreda|March on the Drina|300|false
0003|GG|20.12.2017.|18:00|19:00|cetvrtak|A fistful of Dolars|500|true
0004|GG|21.12.2017.|21:15|00:00|petak|The Good, the Bad and the Ugly|350|true

log0 · Accepted Answer · 2018-01-31 15:30:29Z

0

What you are doing here seems about correct to me but you are only modifying the content of the file loaded in memory, not the file on disk.

You need to write each line to a new file as your are processing lines from projection.txt Something like:

with open('projections.txt') as projections:
    with open('projections-new.txt') as projections_new:
        delete = input("Input projection code you want to delete: ")
        for i in projections:
            projection = i.strip("\n").split("|")
            if delete == projection[0]:
               projection[8]="false"
            projections_new.write("|".join(projection) + "\n")

edited Jan 31, 2018 at 15:30

answered Jan 31, 2018 at 15:22

log0

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