Mastering CSV Files in Python: A Comprehensive Guide

Getting Started with CSV Files

When working with CSV files in Python, we’ll be using the built-in csv module.

Reading CSV Files with csv.reader()

Let’s dive into the basics of using csv.reader() to read CSV files. Suppose we have a CSV file called innovators.csv with the following entries:

with open('innovators.csv', 'r') as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)

CSV Files with Custom Delimiters

By default, CSV files use commas as delimiters. However, some CSV files may use alternative delimiters like | or \t. To read these files, we can pass an additional delimiter parameter to the csv.reader() function.

with open('innovators.csv', 'r') as file:
    reader = csv.reader(file, delimiter='\t')
    for row in reader:
        print(row)

Handling Initial Spaces in CSV Files

Some CSV files may have spaces after delimiters. To remove these initial spaces, we can pass the skipinitialspace parameter to the csv.reader() function.

with open('people.csv', 'r') as file:
    reader = csv.reader(file, skipinitialspace=True)
    for row in reader:
        print(row)

Working with Quoted Entries in CSV Files

CSV files may also contain quoted entries. To handle these, we can use the quoting parameter with the csv.reader() function.

with open('quotes.csv', 'r') as file:
    reader = csv.reader(file, quoting=csv.QUOTE_ALL)
    for row in reader:
        print(row)

Using Dialects in the CSV Module

When working with multiple CSV files, it can become cumbersome to specify formatting patterns individually. That’s where dialects come in. Dialects allow us to group formatting patterns together and reuse them across multiple files.

csv.register_dialect('myDialect', delimiter='|', quoting=csv.QUOTE_ALL, skipinitialspace=True)

with open('office.csv', 'r') as file:
    reader = csv.reader(file, dialect='myDialect')
    for row in reader:
        print(row)

Reading CSV Files with csv.DictReader()

The csv.DictReader() class allows us to read CSV files as dictionaries.

with open('people.csv', 'r') as file:
    reader = csv.DictReader(file)
    for row in reader:
        print(dict(row))

Using the csv.Sniffer Class

The csv.Sniffer class is used to deduce the format of a CSV file. It offers two methods: sniff() and has_header().

with open('office.csv', 'r') as file:
    sample = file.read(64)
    sniffer = csv.Sniffer()
    has_header = sniffer.has_header(sample)
    print(has_header)

    deduced_dialect = sniffer.sniff(sample)
    with open('office.csv', 'r') as file:
        reader = csv.reader(file, dialect=deduced_dialect)
        for row in reader:
            print(row)