How to save the contents of a for loop in a variable

Question

Hey so i have a program here that reads into a CSV file which i created earlier

import csv
import psycopg2
with open('C:\\Users\\Danis Porovic\\PycharmProjects\\Module1\\berichten.csv', 'r') as csv_file:
    csv_reader = csv.reader(csv_file)

    for line in csv_reader:
        print(line)

the for loop gives this as a result

['vies', 'Mon 07 Nov 2022 18:43', 'Mia', 'Haarlem']
['vies', 'Mon 07 Nov 2022 18:43', 'Mia', 'Amsterdam']
['vies', 'Mon 07 Nov 2022 18:43', 'Mia', 'Sittard']
['vies', 'Mon 07 Nov 2022 18:43', 'Mia', 'Venlo']
['vies', 'Mon 07 Nov 2022 18:43', 'Mia', 'Helmond']
['Het zou wel wat schoner mogen zijn', 'Tue 08 Nov 2022 00:49', 'Tijmen', 'Hilversum']
['Het zou wel wat schoner mogen zijn', 'Tue 08 Nov 2022 00:49', 'anoniem', 'Roosendaal']

Now how could i save all this information from the for loop in a single variable?

Create a new list before you start the loop, and append the line to the list on each iteration. — vahndi
– vahndi, Commented Nov 8, 2022 at 1:11
lines = list(csv.reader(csv_file)). No for loop required and this will give you a list of rows. — Mark Tolonen
– Mark Tolonen, Commented Nov 8, 2022 at 1:39
lines = list(csv.reader(csv_file)) is definitely the way to go. Solid answer @Mark Tolonen — Jamie.Sgro
– Jamie.Sgro, Commented Nov 8, 2022 at 1:43

Jamie.Sgro · Accepted Answer · 2022-11-08 01:50:39Z

1

Something like this should do the trick:

result = []
for line in csv_reader:
    result.append(line)

Or using list comprehension:

result = [line for line in csv_reader]

Edit: After comments outlining in more detail what you're looking for. We can transpose the list you usually get so each sublist represents a column from the .csv rather than a row:

import csv
with open('a.csv', 'r') as csv_file:
    regular_list = list(csv.reader(csv_file))
    transposed_result = list(map(list, zip(*regular_list)))
    print(transposed_result)

Shoutout to @Mark Tolonen for removing the for loop iteration and jumping right to csv.reader(csv_file)

edited Nov 8, 2022 at 1:50

answered Nov 8, 2022 at 1:11

Jamie.Sgro

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9 Comments

Danxs Over a year ago

The method above did display all the information but not in the way i want it to. I would like to have each line as a list. This so i can use indexing on it later.

Jamie.Sgro Over a year ago

We currently have a list of lists, where the sublist has many strings. Were you still hoping for a list of lists, but in a different format? Say... the first list is ['vies', 'vies', etc.]? Or did you want a single list, where we've concatenated the sublist into single strings? What did you have in mind in particular?

Danxs Over a year ago

The CSV files is structured in this way: 'Message', Date and Time', 'Name', 'Station' I would like to save the information from the for loop in a variable so that i can use indexing on the list later on and grab all the messages for instance. So for every line create a list with 4 strings in it

Jamie.Sgro Over a year ago

I'm not sure I follow. We currently have list, where each item is a list with 4 strings which allows for indexing. When you say 'variable' do you mean dictionary? If so that'd allow you to look up values e.g. result[0]["Message"] would output "vies". Right not result[0][0] outputs "vies"

Danxs Over a year ago

I would like to have a variable contain the exact information which i gathered with the for loop. So that with index[0] i can get all the messages, with index[1] all the dates, with index[2] all the names etc.

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