How to Write a CSV File in Python

If you want to save table-like data in Python, a CSV file is a common choice.

A CSV file stores data in rows and columns. Python includes a built-in csv module that makes writing CSV files much easier and safer than building the text yourself.

This page shows you how to:

Create a new CSV file in Python
Write one row or many rows
Use the built-in csv module
Understand when to use csv.writer() and csv.DictWriter()

Quick answer

import csv

rows = [
    ["name", "age", "city"],
    ["Alice", 30, "London"],
    ["Bob", 25, "Paris"]
]

with open("people.csv", "w", newline="", encoding="utf-8") as file:
    writer = csv.writer(file)
    writer.writerows(rows)

Use newline="" when opening the file. This helps prevent extra blank lines in CSV output.

The simplest way to write a CSV file

The basic steps are:

Import the csv module
Open the file in write mode using "w"
Use newline="" when opening the file
Create a writer with csv.writer(file)
Write rows with writer.writerow() or writer.writerows()

Example:

import csv

with open("people.csv", "w", newline="", encoding="utf-8") as file:
    writer = csv.writer(file)

    writer.writerow(["name", "age", "city"])
    writer.writerow(["Alice", 30, "London"])
    writer.writerow(["Bob", 25, "Paris"])

This creates a file named people.csv.

Its contents will look like this:

name,age,city
Alice,30,London
Bob,25,Paris

If you are not sure how open() works, see the Python open() function explained. For a broader overview of CSV tools, see the Python csv module overview.

Write one row at a time

Use writer.writerow() when you want to write a single row.

This is useful when:

You are building rows inside a loop
You only need to add one line at a time
Your data is not stored in one big list yet

Each list becomes one row in the CSV file.

Example:

import csv

names = ["Alice", "Bob", "Cara"]

with open("names.csv", "w", newline="", encoding="utf-8") as file:
    writer = csv.writer(file)

    writer.writerow(["name"])

    for name in names:
        writer.writerow([name])

Important detail:

writer.writerow() expects one row
That row is usually a list or tuple

For example, this is correct:

writer.writerow(["Alice", 30, "London"])

A common beginner mistake is passing a plain value instead of a list.

Write many rows at once

Use writer.writerows() when you already have a list of rows.

Each inner list becomes one CSV row.

Example:

import csv

rows = [
    ["name", "age", "city"],
    ["Alice", 30, "London"],
    ["Bob", 25, "Paris"],
    ["Cara", 28, "Berlin"]
]

with open("people.csv", "w", newline="", encoding="utf-8") as file:
    writer = csv.writer(file)
    writer.writerows(rows)

This is a good choice for small, ready-made datasets.

Use:

writerow() for one row
writerows() for multiple rows

Write CSV files with column names

Use csv.DictWriter() when your data is stored as dictionaries.

This is helpful when:

Your data has named fields like "name" and "age"
You want to control the column order
You want cleaner code when working with structured data

Set fieldnames to choose the column order, then call writeheader() to write the first row.

Example:

import csv

rows = [
    {"name": "Alice", "age": 30, "city": "London"},
    {"name": "Bob", "age": 25, "city": "Paris"}
]

with open("people.csv", "w", newline="", encoding="utf-8") as file:
    writer = csv.DictWriter(file, fieldnames=["name", "age", "city"])

    writer.writeheader()
    writer.writerows(rows)

This creates:

name,age,city
Alice,30,London
Bob,25,Paris

Why use DictWriter()?

The column names are clear
You do not need to remember the position of each value
You control the output order with fieldnames

Important file options to use

When writing CSV files, these options matter:

encoding="utf-8" for text data
newline="" for CSV files
"w" to overwrite an existing file
"a" to add rows instead of replacing the file

Example using append mode:

import csv

new_row = ["Dana", 31, "Rome"]

with open("people.csv", "a", newline="", encoding="utf-8") as file:
    writer = csv.writer(file)
    writer.writerow(new_row)

This adds a row to the end of the file instead of replacing it.

If you want to learn more about appending, see how to append to a file in Python.

Common problems beginners run into

Here are the most common mistakes when writing CSV files:

Forgetting to import csv
Opening the file without newline=""
Using "w" when you meant to append with "a"
Passing a plain value instead of a list to writerow()
Using DictWriter without matching fieldnames

Extra blank lines

If your CSV file has blank lines between rows, the usual cause is missing newline="".

Wrong:

with open("people.csv", "w", encoding="utf-8") as file:
    writer = csv.writer(file)

Correct:

with open("people.csv", "w", newline="", encoding="utf-8") as file:
    writer = csv.writer(file)

Badly formatted rows

Do not build CSV lines yourself with commas like this:

name = "Alice"
age = 30
line = name + "," + str(age)

This may break if values contain commas or quotes.

Use the csv module instead.

DictWriter key problems

With csv.DictWriter(), the dictionary keys should match the fieldnames.

Example:

import csv

row = {"name": "Alice", "age": 30, "country": "UK"}

with open("people.csv", "w", newline="", encoding="utf-8") as file:
    writer = csv.DictWriter(file, fieldnames=["name", "age", "city"])
    writer.writeheader()
    writer.writerow(row)

This can cause problems because "country" does not match "city".

Overwriting your data

If you open a file with "w", Python replaces the file contents.

Use "a" if you want to keep the old data and add new rows.

When not to use this method

This method is a good beginner-friendly choice, but not every approach is a good idea.

Avoid manually joining values with commas for real CSV work.

Why?

Values may contain commas
Values may contain quotes
CSV escaping rules can be tricky

Use the csv module when values may contain commas or quotes.

For advanced data analysis, a library like pandas can be easier, but beginners usually do not need it just to create a CSV file.

Debugging tips

If your code is not working, these quick checks can help:

print(rows)
print(type(rows))
print(type(rows[0]))
print(file.name)

import os
print(os.path.exists("people.csv"))

These checks help you answer questions like:

Is rows really a list?
Is each row a list or dictionary?
What file name are you writing to?
Was the file actually created?

If you need to check whether the file exists, see how to check if a file exists in Python.

FAQ

How do I write a header row in a CSV file?

With csv.writer(), write the header as the first row.

writer.writerow(["name", "age", "city"])

With csv.DictWriter(), use writeheader().

writer.writeheader()

Why are there blank lines in my CSV file?

Usually because the file was not opened with newline="".

What is the difference between `writerow()` and `writerows()`?

writerow() writes one row
writerows() writes multiple rows

Should I use `csv.writer()` or `csv.DictWriter()`?

Use:

csv.writer() for lists
csv.DictWriter() for dictionaries with named columns