csv

The csv library lets you read and write CSV files. CSV stands for Comma-Separated Values — it’s a simple file format that spreadsheet apps like Excel and Google Sheets use.

A CSV file looks like this:


name,grade,score
Alice,10,92
Bob,11,85
Carol,10,78

Each row is a record, and commas separate the columns.


import csv

Reading a CSV File


import csv
 
with open("students.csv") as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)
 
# ['name', 'grade', 'score']
# ['Alice', '10', '92']
# ['Bob', '11', '85']

Each row is a list of strings. The first row is usually the header.

Skipping the Header


with open("students.csv") as file:
    reader = csv.reader(file)
    next(reader)  # skip the header row
    for row in reader:
        name, grade, score = row
        print(f"{name} scored {score}")

Reading as Dictionaries

csv.DictReader gives you each row as a dictionary, using the header row as keys. This is usually easier to work with.


with open("students.csv") as file:
    reader = csv.DictReader(file)
    for row in reader:
        print(row["name"], row["score"])

Writing a CSV File


import csv
 
with open("output.csv", "w", newline="") as file:
    writer = csv.writer(file)
    writer.writerow(["name", "score"])   # header
    writer.writerow(["Alice", 92])
    writer.writerow(["Bob", 85])

All values read from a CSV come back as strings, even numbers. Use int() or float() to convert them if you need to do math.


score = int(row["score"])   # convert "92" → 92