Rename column and reformat data of multiple CSV files

Question

I have a folder CSV files containing lines as follows:

Date      | A | B | C |
2021-10-11| A | B | C |

I would like to rearrange the date column across every file, for instance, from 2021-10-11 to 10/11/2021.

Answer 1

Use the pathlib, datetime and csv modules

To import your data use the csv module and flip the dates you will need a csv reader and a csv writer. Using the DictReader and DictWriter classes can be convenient.

Converting dates is pretty simple using the datetime module.

import csv
from datetime import datetime

old_fmt = '%Y-%m-%d'
new_fmt = '%m/%d/%Y'

def process_file(path):
    # read the data in
    with path.open('r') as f:
        reader = csv.DictReader(f)
        fieldnames = reader.fieldnames
        data = list(reader)

    # write the data out
    with path.open('w') as f:
        writer = csv.DictWriter(f, fieldnames=fieldnames)
        writer.writeheader()
        for row in data:
            # here we convert the format
            dt = datetime.strptime(row['date'], old_fmt)
            row['date'] = dt.strftime(new_fmt)
            writer.writerow(row)

pathlib is a great module for working with the filesystem. Its easy to process all the files.

from pathlib import Path

folder = Path('path/to/directory')

for path in folder.iterdir():
    if path.is_file():
        process_file(path)