Working with CSV files in Python

Introduction

CSV files store data in a simple table format. Learning to work with them helps you read and save data easily.

You want to save a list of contacts from your program to a file.

You need to read data from a spreadsheet saved as CSV.

You want to share data with others in a simple text format.

You want to process data exported from a database or website.

You want to automate reading or writing data in a format many programs understand.

Syntax

Python

import csv

# Reading CSV file
with open('file.csv', newline='') as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)

# Writing CSV file
with open('file.csv', 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(['Name', 'Age'])
    writer.writerow(['Alice', 30])

Use newline='' when opening files to avoid extra blank lines on some systems.

csv.reader reads rows as lists of strings.

Examples

This reads each row from data.csv and prints it as a list.

Python

import csv

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

This writes two rows to output.csv: a header and one data row.

Python

import csv

with open('output.csv', 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(['City', 'Country'])
    writer.writerow(['Paris', 'France'])

DictReader reads rows as dictionaries using the header row as keys.

Python

import csv

with open('people.csv', newline='') as file:
    reader = csv.DictReader(file)
    for row in reader:
        print(row['Name'], row['Age'])

DictWriter writes rows using dictionary keys matching the header fields.

Python

import csv

with open('people.csv', 'w', newline='') as file:
    fieldnames = ['Name', 'Age']
    writer = csv.DictWriter(file, fieldnames=fieldnames)
    writer.writeheader()
    writer.writerow({'Name': 'Bob', 'Age': 25})

Sample Program

This program first writes two rows of data to sample.csv. Then it reads the file and prints each row as a list.

Python

import csv

# Write sample data to CSV
with open('sample.csv', 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(['Name', 'Score'])
    writer.writerow(['Alice', 85])
    writer.writerow(['Bob', 90])

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

Important Notes

CSV files separate values by commas by default, but you can change the separator with the delimiter option.

Always close files or use with to handle files safely.

When reading, all data is read as text (strings). Convert to numbers if needed.

Summary

CSV files store data in rows and columns separated by commas.

Use Python's csv module to read and write CSV files easily.

Use csv.reader for simple lists and csv.DictReader for named columns.