9.12.1 Python Standard Library Module csv

• csv module provides functions for working with CSV files

Writing to a CSV File

• csv module’s documentation recommends opening CSV files with the additional keyword argument newline='' to ensure that newlines are processed properly

import csv

with open('accounts.csv', mode='w', newline='') as accounts:
    writer = csv.writer(accounts)
    writer.writerow([100, 'Jones', 24.98])
    writer.writerow([200, 'Doe', 345.67])
    writer.writerow([300, 'White', 0.00])
    writer.writerow([400, 'Stone', -42.16])
    writer.writerow([500, 'Rich', 224.62])

• .csv file extension indicates a CSV-format file
• writer function returns an object that writes CSV data to the specified file object
• writer’s writerow method receives an iterable to store in the file
• By default, writerow delimits values with commas, but you can specify custom delimiters

!cat accounts.csv

100,Jones,24.98
200,Doe,345.67
300,White,0.0
400,Stone,-42.16
500,Rich,224.62

• writerow calls above can be replaced with one writerows call that outputs a comma-separated list of iterables representing the records
• If you write data that contains commas in a given string, writerow encloses that string in double quotes to indicate a single value

Reading from a CSV File

• Read records from the file accounts.csv and display the contents of each record

with open('accounts.csv', 'r', newline='') as accounts:
    print(f'{"Account":<10}{"Name":<10}{"Balance":>10}')
    reader = csv.reader(accounts)
    for record in reader:  
        account, name, balance = record
        print(f'{account:<10}{name:<10}{balance:>10}')

Account   Name         Balance
100       Jones          24.98
200       Doe           345.67
300       White            0.0
400       Stone         -42.16
500       Rich          224.62

• csv module’s reader function returns an object that reads CSV-format data from the specified file object
• Can iterate through the reader object one record of comma-delimited values at a time

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