Change date formats in csv with Python 3

Question

I need to exchange dateformats in a large csv from DD/MM/YYYY to YYYY-MM-DD. I have no problem printing out the values I want them to replace with, but I have a hard time actually overwriting the csv.

Here is my code:

import csv
from datetime import datetime

with open('partner_new_testteam.csv', newline='') as data:
    reader = csv.reader(data)

    for list in reader:
        for string in list:
            try:
                datetimeobject = datetime.strptime(string, '%d/%m/%Y')
                changedDate = datetimeobject.strftime('%Y-%m-%d')
                print(changedDate)

            except:
                continue

I know this code is rather sloppy, but keep in mind that I just started programming, thanks in advance!

tzv · Accepted Answer · 2018-11-14 16:07:52Z

2

import csv
import re
from datetime import datetime

lines = []
# open file as read-only
with open('partner_new_testteam.csv', "r", newline='') as data:
    reader = csv.reader(data)
    # go over all of its rows, and the row's items and change 
    # items that match the date format
    for row in reader:
        for i, string in enumerate(row):
            if re.match(r"\d+\/\d+\/\d+", string):
                datetimeobject = datetime.strptime(string, '%d/%m/%Y')
                new_string = datetimeobject.strftime('%Y-%m-%d')
                row[i] = new_string
                print("Replaced", string, "with", new_string)
        # save edited, and originally correct ones to new list
        new_row = row
        lines.append(new_row)

# write new rows by overwriting original file
with open('partner_new_testteam.csv', "w", newline='') as data:
    writer = csv.writer(data)
    writer.writerows(lines)

Your current code does not actually change anything. You never replaced anything and you didn't open the file with write access.

You also should not use try: like it is an if. The regex matches x/x/x, where x is any amount of numbers.

edited Nov 14, 2018 at 16:07

answered Nov 14, 2018 at 15:49

tzv

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1 Comment

Vinni Over a year ago

It worked thanks a mill!! Another question... It makes sense when I see your code now, but if I had to do it myself I would be completely lost. Is that something that comes just with experience?

Lustra Loremipsum · Accepted Answer · 2018-11-14 14:57:35Z

0

The .csv file is opened read-only per your 'open' command.

You need to pass the 'w' parameter to the 'open' command.

answered Nov 14, 2018 at 14:57

Lustra Loremipsum

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Comments

iamklaus · Accepted Answer · 2018-11-14 15:01:35Z

0

read csv using pandas -> pd.read_csv and then use pd.to_datetime

eg.

data = pd.DataFrame()

data['A'] = ['11/12/2018']

print(data)

            A
0  11/12/2018

using pd.to_datetime

data.A = pd.to_datetime(data['A'])

print(data)

           A
0 2018-11-12

answered Nov 14, 2018 at 15:01

iamklaus

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