Writing CSV files in Python
Last Updated :
12 Jul, 2025
CSV (Comma Separated Values) is a simple file format used to store tabular data, such as spreadsheets or databases. Each line of the file represents a data record, with fields separated by commas. This format is popular due to its simplicity and wide support.
Ways to Write CSV Files in Python
Below are the ways by which we can write CSV files in Python:
1. Using csv.DictWriter() :
The csv.DictWriter class maps dictionaries onto output rows, allowing you to write data where each row is represented by a dictionary.
Syntax:
csv.DictWriter(csvfile, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds)
Where:
- csvfile: A file object with a write() method.
- fieldnames: A sequence of keys identifying the order in which values should be written.
- restval (optional): Default value to be written if a dictionary is missing a key in fieldnames.
- extrasaction (optional): Action to take if a key not found in fieldnames is encountered. Setting it to 'raise' will raise a ValueError.
- dialect (optional): Name of the dialect to be used.
Example:
Python
import csv
data = [
{'name': 'Nikhil', 'branch': 'COE', 'year': 2, 'cgpa': 9.0},
{'name': 'Sanchit', 'branch': 'COE', 'year': 2, 'cgpa': 9.1},
{'name': 'Aditya', 'branch': 'IT', 'year': 2, 'cgpa': 9.3},
{'name': 'Sagar', 'branch': 'SE', 'year': 1, 'cgpa': 9.5},
{'name': 'Prateek', 'branch': 'MCE', 'year': 3, 'cgpa': 7.8},
{'name': 'Sahil', 'branch': 'EP', 'year': 2, 'cgpa': 9.1}
]
with open('university_records.csv', 'w', newline='') as csvfile:
fieldnames = ['name', 'branch', 'year', 'cgpa']
writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
writer.writeheader()
writer.writerows(data)
In this example, student records are stored as dictionaries, and a CSV file named "university_records.csv" is generated using these dictionaries. The `csv.DictWriter` class is utilized to write the field names as headers and the dictionary data rows to the CSV file.
Output:
name,branch,year,cgpa
Nikhil,COE,2,9.0
Sanchit,COE,2,9.1
Aditya,IT,2,9.3
Sagar,SE,1,9.5
Prateek,MCE,3,7.8
Sahil,EP,2,9.1
2. Using csv.writer()
The csv.writer class is used to write data directly to a CSV file. It handles the conversion of data to a delimited string format.
Syntax:
csv.writer(csvfile, dialect='excel', **fmtparams)
Where:
- csvfile: A file object with a write() method.
- dialect (optional): Name of the dialect to be used.
- fmtparams (optional): Formatting parameters that override those specified in the dialect.
Example:
Python
import csv
data = [
['Name', 'Branch', 'Year', 'CGPA'],
['Nikhil', 'COE', 2, 9.0],
['Sanchit', 'COE', 2, 9.1],
['Aditya', 'IT', 2, 9.3],
['Sagar', 'SE', 1, 9.5],
['Prateek', 'MCE', 3, 7.8],
['Sahil', 'EP', 2, 9.1]
]
with open('university_records.csv', 'w', newline='') as csvfile:
writer = csv.writer(csvfile)
writer.writerows(data)
Output:
name,branch,year,cgpa
Nikhil,COE,2,9.0
Sanchit,COE,2,9.1
Aditya,IT,2,9.3
Sagar,SE,1,9.5
Prateek,MCE,3,7.8
Sahil,EP,2,9.1
Advanced CSV Writing
i) Creating CSV Files with Pipe Delimiters
To use a delimiter other than a comma, specify the delimiter when creating the writer object.
Python
import csv
data = [
['Name', 'Age', 'City'],
['Alice', 25, 'New York'],
['Bob', 30, 'Los Angeles'],
['Charlie', 35, 'Chicago']
]
with open('data_pipe_delimited.csv', 'w', newline='') as csvfile:
writer = csv.writer(csvfile, delimiter='|')
writer.writerows(data)
Output:
Name|Age|City
Alice|25|New York
Bob|30|Los Angeles
Charlie|35|Chicago
ii) Writing CSV Files with Custom Quoting Characters
We can customize the quoting character used in the CSV file.
Python
import csv
data = [
['Nikhil', 'COE', 2, 9.0],
['Sanchit', 'COE', 2, 9.1],
['Aditya', 'IT', 2, 9.3],
['Sagar', 'SE', 1, 9.5],
['Prateek', 'MCE', 3, 7.8],
['Sahil', 'EP', 2, 9.1]
]
with open('students_data.csv', 'w', newline='') as csvfile:
writer = csv.writer(csvfile, quotechar='~', delimiter='|', quoting=csv.QUOTE_ALL)
writer.writerows(data)
Output:
~Nikhil~|~COE~|~2~|9.0
~Sanchit~|~COE~|~2~|9.1
~Aditya~|~IT~|~2~|9.3
~Sagar~|~SE~|~1~|9.5
~Prateek~|~MCE~|~3~|7.8
~Sahil~|~EP~|~2~|9.1
iii) Using 'escapechar' in CSV Writer
To handle special characters within the data, we can specify an escape character.
Python
import csv
data = [
['Nikhil', 'COE', 2, '9.0'],
['Sanchit', 'COE', 2, '9.1'],
['Aditya', 'IT', 2, '9.3'],
['Sagar', 'SE', 1, '9.5'],
['Prateek', 'MCE', 3, '7.8'],
['Sahil', 'EP', 2, '9.1']
]
with open('students.csv', 'w', newline='') as csvfile:
writer = csv.writer(csvfile, delimiter='|', quotechar='"', escapechar='\\')
writer.writerows(data)
Output:
Nikhil|COE|2|9.0
Sanchit|COE|2|9.1
Aditya|IT|2|9.3
Sagar|SE|1|9.5
Prateek|MCE|3|7.8
Sahil|EP|2|9.1
Write into CSV Files Using csv.writer()
csv.writer
class is used to insert data to the CSV file. This class returns a writer object which is responsible for converting the user’s data into a delimited string. A csvfile object should be opened with newline=''
otherwise, newline characters inside the quoted fields will not be interpreted correctly.
Syntax: csv.writer(csvfile, dialect=’excel’, **fmtparams)
Parameters:
- csvfile: A file object with write() method.
- dialect (optional): Name of the dialect to be used.
- fmtparams (optional): Formatting parameters that will overwrite those specified in the dialect.
In this example, a CSV file named "university_records.csv" is created and populated with student records. The file contains fields such as Name, Branch, Year, and CGPA. The data rows for individual students are written to the CSV file, followed by the field names.
Python
import csv
# field names
fields = ['Name', 'Branch', 'Year', 'CGPA']
# data rows of csv file
rows = [['Nikhil', 'COE', '2', '9.0'],
['Sanchit', 'COE', '2', '9.1'],
['Aditya', 'IT', '2', '9.3'],
['Sagar', 'SE', '1', '9.5'],
['Prateek', 'MCE', '3', '7.8'],
['Sahil', 'EP', '2', '9.1']]
# name of csv file
filename = "university_records.csv"
# writing to csv file
with open(filename, 'w') as csvfile:
# creating a csv writer object
csvwriter = csv.writer(csvfile)
# writing the fields
csvwriter.writerow(fields)
# writing the data rows
csvwriter.writerows(rows)
Output:
Name,Branch,Year,CGPA
Nikhil,COE,2,9.0
Sanchit,COE,2,9.1
Aditya,IT,2,9.3
Sagar,SE,1,9.5
Prateek,MCE,3,7.8
Sahil,EP,2,9.1
Creating CSV Files in Python Having Pipe Delimiter
In this example, a CSV file named "data_pipe_delimited.csv" is generated with data rows separated by pipe (|
) delimiters. The file contains information on individuals' names, ages, and cities.
Python
import csv
# Define the data to be written to the CSV file
data = [
['Name', 'Age', 'City'],
['Alice', 25, 'New York'],
['Bob', 30, 'Los Angeles'],
['Charlie', 35, 'Chicago']
]
# Specify the file name
filename = 'data_pipe_delimited.csv'
# Write data to the CSV file with a pipe delimiter
with open(filename, 'w', newline='') as csvfile:
csvwriter = csv.writer(csvfile, delimiter='|')
csvwriter.writerows(data)
print(f"Data has been written to {filename}")
Output:
Name|Age|City
Alice|25|New York
Bob|30|Los Angeles
Charlie|35|Chicago
Write CSV Files with Quotes
In this example, a CSV file named "students_data.csv" is generated with each field enclosed in double quotes. The file contains information about students' names, branches, years, and CGPA scores.
Python
import csv
# Define the rows data
rows = [
['Nikhil', 'COE', '2', '9.0'],
['Sanchit', 'COE', '2', '9.1'],
['Aditya', 'IT', '2', '9.3'],
['Sagar', 'SE', '1', '9.5'],
['Prateek', 'MCE', '3', '7.8'],
['Sahil', 'EP', '2', '9.1']
]
# Specify the file name
filename = 'students_data.csv'
# Write the rows data to the CSV file with quotes around each field
with open(filename, 'w', newline='') as csvfile:
csvwriter = csv.writer(csvfile, quoting=csv.QUOTE_ALL)
csvwriter.writerows(rows)
print(f"Data has been written to {filename}")
Output:
"Nikhil","COE","2","9.0"
"Sanchit","COE","2","9.1"
"Aditya","IT","2","9.3"
"Sagar","SE","1","9.5"
"Prateek","MCE","3","7.8"
"Sahil","EP","2","9.1"
Writing CSV Files with Custom Quoting Character
In this example, a CSV file named "students_data.csv" is created with fields separated by pipe (|
) delimiters and enclosed in tildes (~
). The data includes student names, branches, years, and CGPA scores.
Python
import csv
rows = [
['Nikhil', 'COE', '2', '9.0'],
['Sanchit', 'COE', '2', '9.1'],
['Aditya', 'IT', '2', '9.3'],
['Sagar', 'SE', '1', '9.5'],
['Prateek', 'MCE', '3', '7.8'],
['Sahil', 'EP', '2', '9.1']
]
filename = 'students_data.csv'
with open(filename, 'w', newline='') as file:
writer = csv.writer(file, quoting=csv.QUOTE_NONNUMERIC,
delimiter='|', quotechar='~')
writer.writerows(rows)
print(f"Data has been written to {filename}")
Output:
~Nikhil~|~COE~|~2~|9.0
~Sanchit~|~COE~|~2~|9.1
~Aditya~|~IT~|~2~|9.3
~Sagar~|~SE~|~1~|9.5
~Prateek~|~MCE~|~3~|7.8
~Sahil~|~EP~|~2~|9.1
Using ''escapechar'' in CSV
In this example, a CSV file named "students.csv" is generated with fields separated by pipe (|
) delimiters. The quotechar
is set to double quotes ("
) and the escapechar
is set to backslash (\\
), allowing for proper handling of quotes within the data.
Python
import csv
rows = [
['Nikhil', 'COE', '2', '9.0'],
['Sanchit', 'COE', '2', '9.1'],
['Aditya', 'IT', '2', '9.3'],
['Sagar', 'SE', '1', '9.5'],
['Prateek', 'MCE', '3', '7.8'],
['Sahil', 'EP', '2', '9.1']
]
filename = 'students.csv'
with open(filename, 'w', newline='') as file:
writer = csv.writer(file, quoting=csv.QUOTE_NONE,
delimiter='|', quotechar='"', escapechar='\\')
writer.writerows(rows)
print(f"Data has been written to {filename}")
Output:
Nikhil|COE|2|9.0
Sanchit|COE|2|9.1
Aditya|IT|2|9.3
Sagar|SE|1|9.5
Prateek|MCE|3|7.8
Sahil|EP|2|9.1
Conclusion
Writing CSV files in Python is a straightforward and flexible process, thanks to the csv module. Whether you are working with simple lists, dictionaries, or need to handle more complex formatting requirements such as custom delimiters or quoting characters, the csv.writer and csv.DictWriter classes provide the tools you need.
Key points to remember:
- newline='' Usage: Always open the file with newline='' to prevent extra blank lines in your CSV output.
- Flexibility: Customize delimiters, quoting, and escape characters to suit your data requirements.
- Ease of Use: Write data from lists or dictionaries easily using csv.writer and csv.DictWriter.
By understanding and utilizing these methods, you can efficiently export your data into CSV files, making it accessible for various applications, from data analysis to data sharing.
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