Working with CSV Files

CSV (Comma-Separated Values) files store tabular data.

Reading CSV

import csv

# Read CSV file
with open('data.csv', 'r') as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)

# Read as dictionaries
with open('data.csv', 'r') as file:
    reader = csv.DictReader(file)
    for row in reader:
        print(row['name'], row['age'])

Writing CSV

import csv

# Write rows
with open('output.csv', 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(['Name', 'Age', 'City'])
    writer.writerow(['Alice', 25, 'NYC'])
    writer.writerow(['Bob', 30, 'LA'])

# Write from dictionaries
data = [
    {'name': 'Alice', 'age': 25},
    {'name': 'Bob', 'age': 30}
]

with open('output.csv', 'w', newline='') as file:
    fieldnames = ['name', 'age']
    writer = csv.DictWriter(file, fieldnames=fieldnames)
    writer.writeheader()
    writer.writerows(data)

Custom Delimiters

# Tab-separated values
with open('data.tsv', 'r') as file:
    reader = csv.reader(file, delimiter='\t')
    
# Semicolon-separated
with open('data.csv', 'r') as file:
    reader = csv.reader(file, delimiter=';')

Practice Exercises

1. Read CSV and calculate statistics
2. Write data to CSV from list
3. Filter CSV data
4. Merge multiple CSV files
5. Convert CSV to JSON

Next Lesson: JSON Files