saving python variable to csv

Question

i am having troubles on this python error. I want to save changing variables to an csv file, however while the code runs again with an different variable it overwrites the previous one. I do not have the variables predetermined, they are generated while the code runs, so every time the loop will loop the program there will a different email passed.

Here is my code:

import csv

def hello(hme):
        header = ['email']
        data = [hme]


        with open('countries.csv', 'w', encoding='UTF8', newline='') as f:
                writer = csv.writer(f)


                writer.writerow(header)
                writer.writerows(data)

hello(["[email protected]"])

Thank you!

Probably easier to use pandas data frame and then covert to csv through pandas.DataFrame.to_csv — VRComp
– VRComp, Commented Jun 15, 2022 at 13:32
if you don't want to overwrite the existing value open the file in append mode — user2261062
– user2261062, Commented Jun 15, 2022 at 13:34
@VRComp Bringing in a pandas dependency seems quite overkill for this simple task… — Spok
– Spok, Commented Jun 15, 2022 at 13:35
@NicolasMoreau Good point. I was thinking maybe OP will expand the code to include more rows, which is why I suggested pandas. This could be a simple case and OP wanted to apply it to a larger case later on. — VRComp
– VRComp, Commented Jun 15, 2022 at 15:49

Spok · Accepted Answer · 2022-06-15 13:35:05Z

1

you should open the file as append, instead of write: 'a' instead of 'w'

import csv

def hello(hme):
        header = ['email']
        data = [hme]


        with open('countries.csv', 'a', encoding='UTF8', newline='') as f:
                writer = csv.writer(f)


                writer.writerow(header)
                writer.writerows(data)

hello(["[email protected]"])

answered Jun 15, 2022 at 13:35

Spok

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2 Comments

dismaaay Over a year ago

hi thanks for the response, if i write emails manually and delete writer.writerow(header) and header = ['email'] it outputs like this [email protected] and if i keep the header it outputs email #new row email #new row [email protected]

dismaaay Over a year ago

however if i manually type email #new row it just works fine

Majed Jaber · Accepted Answer · 2022-06-15 13:40:07Z

0

Just replace 'w' by 'a' where 'w' writes in file (override) while 'a' appends the file whenever you write in it.

with open('countries.csv', 'a', encoding='UTF8', newline='') as f:

For the header "email" just write it before you add the loop of emails to do not duplicate it

answered Jun 15, 2022 at 13:40

Majed Jaber

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Comments

wwii · Accepted Answer · 2022-06-15 14:18:33Z

0

Read the file contents first; add the new data; write the data to a file.

def hello(hme):
    try:
        with open('countries.csv', encoding='UTF8', newline='') as f:
            stuff = list(csv.reader(f))
    except FileNotFoundError:
        # this must be the first time the function was called
        stuff = [['email']]
    stuff.append([hme])

    with open('countries.csv', 'w', encoding='UTF8', newline='') as f:
        writer = csv.writer(f)
        writer.writerows(stuff)

If your file really only has one column you don't really need to use the csv module. Just append the new line to the file.

# assumes header is present
def hello(hme):
    with open('countries.csv', 'a', encoding='UTF8') as f:
        f.write(hme + '\n')

edited Jun 15, 2022 at 14:18

answered Jun 15, 2022 at 14:02

wwii

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