Summary: in this tutorial, you’ll learn how to write data into a CSV file using the built-in csv
module.
Steps for writing a CSV file
To write data into a CSV file, you follow these steps:
- First, open the CSV file for writing [
w
mode] by using theopen[]
function. - Second, create a CSV writer object by calling the
writer[]
function of thecsv
module. - Third, write data to CSV
file by calling the
writerow[]
orwriterows[]
method of the CSV writer object. - Finally, close the file once you complete writing data to it.
The following code illustrates the above steps:
Code language: Python [python]
import csv # open the file in the write mode f = open['path/to/csv_file', 'w'] # create the csv writer writer = csv.writer[f] # write a row to the csv file writer.writerow[row] # close the file f.close[]
It’ll be shorter if you use the with
statement so that you don’t need to call the close[]
method to explicitly close the file:
import csv # open the file in the write mode with open['path/to/csv_file', 'w'] as f: # create the csv writer writer = csv.writer[f] # write a row to the csv file writer.writerow[row]
Code language: PHP [php]
If you’re dealing with non-ASCII characters, you need to specify the character encoding in the open[]
function.
The following illustrates how to write UTF-8 characters to a CSV file:
Code language: PHP [php]
import csv # open the file in the write mode with open['path/to/csv_file', 'w', encoding='UTF8'] as f: # create the csv writer writer = csv.writer[f] # write a row to the csv file writer.writerow[row]
Writing to CSV files example
The following example shows how to write data to the CSV file:
Code language: PHP [php]
import csv header = ['name', 'area', 'country_code2', 'country_code3'] data = ['Afghanistan', 652090, 'AF', 'AFG'] with open['countries.csv', 'w', encoding='UTF8'] as f: writer = csv.writer[f] # write the header writer.writerow[header] # write the data writer.writerow[data]
If you open the countries.csv
, you’ll see one issue that the file contents have an additional blank line between two subsequent rows:
To remove the blank line, you pass the keyword argument newline=''
to the open[]
function as follows:
Code language: PHP [php]
import csv header = ['name', 'area', 'country_code2', 'country_code3'] data = ['Afghanistan', 652090, 'AF', 'AFG'] with open['countries.csv', 'w', encoding='UTF8', newline=''] as f: writer = csv.writer[f] # write the header writer.writerow[header] # write the data writer.writerow[data]
Output:
Writing multiple rows to CSV files
To write multiple rows to a CSV file at once, you use the writerows[]
method of the CSV writer object.
The following uses the writerows[]
method to write multiple
rows into the countries.csv
file:
import csv header = ['name', 'area', 'country_code2', 'country_code3'] data = [ ['Albania', 28748, 'AL', 'ALB'], ['Algeria', 2381741, 'DZ', 'DZA'], ['American Samoa', 199, 'AS', 'ASM'], ['Andorra', 468, 'AD', 'AND'], ['Angola', 1246700, 'AO', 'AGO'] ] with open['countries.csv', 'w', encoding='UTF8', newline=''] as f: writer = csv.writer[f] # write the header writer.writerow[header] # write multiple rows writer.writerows[data]
Code language: PHP [php]
Writing to CSV files using the DictWriter class
If each row of the CSV file is a dictionary, you can use the DictWriter
class of the csv
module to write the dictionary to the CSV file.
The example illustrates how to use the DictWriter class to write data to a CSV file:
Code language: PHP [php]
import csv # csv header fieldnames = ['name', 'area', 'country_code2', 'country_code3'] # csv data rows = [ {'name': 'Albania', 'area': 28748, 'country_code2': 'AL', 'country_code3': 'ALB'}, {'name': 'Algeria', 'area': 2381741, 'country_code2': 'DZ', 'country_code3': 'DZA'}, {'name': 'American Samoa', 'area': 199, 'country_code2': 'AS', 'country_code3': 'ASM'} ] with open['countries.csv', 'w', encoding='UTF8', newline=''] as f: writer = csv.DictWriter[f, fieldnames=fieldnames] writer.writeheader[] writer.writerows[rows]
How it works.
- First, define variables that hold the field names and data rows of the CSV file.
- Next, open the CSV file for writing by
calling the
open[]
function. - Then, create a new instance of the
DictWriter
class by passing the file object [f
] andfieldnames
argument to it. - After that, write the header for the CSV file by calling the
writeheader[]
method. - Finally, write data rows to the CSV file using the
writerows[]
method.
Summary
- Use the CSV Writer or the
DictWriter
class to write data to a CSV file.
Did you find this tutorial helpful ?