How to Write CSV File in Python: Simple Guide with Examples

To write a CSV file in Python, use the csv module's writer object. Open a file in write mode, create a writer with csv.writer(file), then use writer.writerow() to add rows.

Syntax

Here is the basic syntax to write rows to a CSV file using Python's csv module:

• Open a file in write mode with open('filename.csv', 'w', newline='').
• Create a CSV writer object with csv.writer(file).
• Use writer.writerow() to write a single row (list of values).
• Use writer.writerows() to write multiple rows at once.

python

import csv

with open('output.csv', 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(['Name', 'Age', 'City'])  # Write header row
    writer.writerow(['Alice', 30, 'New York'])  # Write one data row
    writer.writerows([
        ['Bob', 25, 'Los Angeles'],
        ['Charlie', 35, 'Chicago']
    ])  # Write multiple rows

Example

This example writes a CSV file named people.csv with a header and three rows of data. It shows how to open the file, create the writer, and write rows.

python

import csv

with open('people.csv', 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(['Name', 'Age', 'City'])
    writer.writerow(['Alice', 30, 'New York'])
    writer.writerow(['Bob', 25, 'Los Angeles'])
    writer.writerow(['Charlie', 35, 'Chicago'])

Common Pitfalls

Common mistakes when writing CSV files in Python include:

• Not using newline='' in open(), which can cause extra blank lines on some systems.
• Forgetting to open the file in write mode 'w'.
• Passing strings instead of lists to writer.writerow().
• Not closing the file (using with handles this automatically).

python

import csv

# Wrong: missing newline='' causes blank lines on Windows
with open('wrong.csv', 'w') as file:
    writer = csv.writer(file)
    writer.writerow(['Name', 'Age'])

# Right: use newline='' to avoid blank lines
with open('right.csv', 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(['Name', 'Age'])

Quick Reference

Summary tips for writing CSV files in Python:

• Always import the csv module.
• Open files with newline='' to avoid blank lines.
• Use writer.writerow() for single rows and writer.writerows() for multiple rows.
• Pass rows as lists or tuples, not strings.
• Use with to handle file closing automatically.

Key Takeaways

Use the csv module's writer object to write rows to a CSV file.

Always open the file with newline='' to prevent extra blank lines.

Write rows as lists or tuples using writer.writerow() or writer.writerows().

Use with statement to automatically close the file after writing.

Avoid passing strings directly to writer.writerow(); use iterable of values instead.