Python 3: CSV Module

Question

I am working with a simple csv file and want to know how to update the values contained in a specific cell on each row using data my script has generated.

column1, column2, colum3, column4,
bob, 20, blue, hammer
jane, 30, red, pencil
chris, 40, green, ruler

Then:

new_colour = [pink, yellow, black]

Is there a way to take the list <new_colour> and write each list item into the values under colum3 within the csv file? To have it end up like below:

column1, column2, colum3, column4,
bob, 20, pink, hammer
jane, 30, yellow, pencil
chris, 40, black, ruler

Thank you

'test_domain_application_data.csv' has the data you want to update? You want to read the existing CSV, update the data, then write. What are the rules for what you want to overwrite? make this a small working example and we'll have a better chance at answering. — tdelaney
– tdelaney, Commented Nov 22, 2022 at 23:58
You'll need to load the CSV into your Python script, and write out a new, modified one. If it is very large, do it "on-the-fly" i.e. reading, modifying and writing as you go. If it is small, and it's simpler, read the whole CSV, modify and then write in one go. You can delete or rename the existing CSV as XXX.csv.bkup before writing the new file. If there are other processes simultaneously accessing the CSV while you change it, save the new file as XXX.csv.inprogress till it is completely written then rename it when complete so everyone gets a consistent view. — Mark Setchell
– Mark Setchell, Commented Nov 23, 2022 at 10:05

EEtch · Accepted Answer · 2022-11-23 10:08:34Z

2

One (probably unoptimized) solution could be using the pandas module, as long as your CSV file is not too big:

PATH_TO_CSV = <your_path>
new_colour = ['pink', 'yellow', 'black']

df = pd.read_csv(PATH_TO_CSV)
df['colum3'] = pd.Series(new_colour)
df.to_csv(PATH_TO_CSV)

answered Nov 23, 2022 at 10:08

EEtch

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