Python edit specific row and column of csv file

Question

I have some python code here with the aim of taking user input to target a specific row of a CSV and then to overwrite it if a certain letter matches.

import csv

line_count = 0
marked_item = int(input("Enter the item number:"))
with open("items.csv", 'r') as f:
    reader = csv.reader(f, delimiter=',')
    title = next(reader)
    print(title)
    print(title[3])
    lines = []
    for line in reader:
        if title[3] == 'a':
            line_count += 1
            if marked_item == line_count:
                title[3] = 'b'
        lines.append(line)
with open("items.csv", 'w', newline='') as f:
    writer = csv.writer(f, delimiter=',')
    writer.writerow(title)
    writer.writerows(lines)

This code works almost the way I want it to but it is unable to edit any other row but the first. an example of the output this code is:

red,12.95,2,b #note, this change from 'a' to 'b'
blue,42.5,3,a #How can I target this row and change it?
green,40.0,1,a

the problem I then have it targeting another row like row 'blue,42.5,a'. My code is unable to target and then change the value 'a' to 'b'.

Jean-François Fabre · Accepted Answer · 2016-10-20 08:41:16Z

5

you're iterating on line and you change title. Do this:

for line in reader:
    if len(line)>3 and line[3] == 'a':
        line_count += 1
        if marked_item == line_count:
            line[3] = 'b'
    lines.append(line)

and drop the title = next(reader) since you don't have a title.

full fixed code for input csvs that don't have a title line:

import csv

line_count = 0
marked_item = int(input("Enter the item number:"))
with open("items.csv", 'r') as f:
    reader = csv.reader(f, delimiter=',')

    lines = []
    for line in reader:
        if len(line)>3 and line[3] == 'a':
            line_count += 1
            if marked_item == line_count:
                line[3] = 'b'
        lines.append(line)
with open("items.csv", 'w', newline='') as f:
    writer = csv.writer(f, delimiter=',')
    writer.writerow(title)
    writer.writerows(lines)

edited Oct 20, 2016 at 8:41

answered Oct 20, 2016 at 8:17

Jean-François Fabre♦

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4 Comments

core_light Over a year ago

I have tried doing this originally but I get this error: 'if line[3] == 'r': IndexError: list index out of range'

core_light Over a year ago

note that the 'r' in 'if line[3] == 'r' '. I changed my code to reflect 'r' instead of 'a'

Jean-François Fabre Over a year ago

You must have empty lines. I have added a length check on the row.

core_light Over a year ago

actually, I just tried the top code you put in there. thats working now, thank you very much

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