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How to append a new row to an existing csv file?

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  • Difficulty Level : Medium
  • Last Updated : 26 Nov, 2020

For appending a new row to an existing CSV file we have many ways to do that. Here we will discuss 2 ways to perform this task effectively. So, we have 2 ways first is ‘Append a list as a new row to the existing CSV file’ and the second way is ‘Append a dictionary as a new row to the existing CSV file’.

First, let’s have a look at our existing CSV file contents. Suppose we have CSV file event.csv which has the below contents.

CSV file before append

For writing a CSV file, the CSV module provides two different classes writer and Dictwriter.

Append a list as a new row to the existing CSV file

let’s see how to use writer class to append a list as a new row into an existing CSV file. There are several steps to take that.

  • Import writer class from csv module
  • Open your existing CSV file in append mode
    Create a file object for this file.
  • Pass this file object to csv.writer() and get a writer object.
  • Pass the list as an argument into the writerow() function of the writer object.
    (It will add a list as a new row into the CSV file).
  • Close the file object

Let’s take one List that we want to add as a new row.

List=[6,'William',5532,1,'UAE']

Now apply the above steps to the program.

Python3




# Import writer class from csv module
from csv import writer
  
# List 
List=[6,'William',5532,1,'UAE']
  
# Open our existing CSV file in append mode
# Create a file object for this file
with open('event.csv', 'a') as f_object:
  
    # Pass this file object to csv.writer()
    # and get a writer object
    writer_object = writer(f_object)
  
    # Pass the list as an argument into
    # the writerow()
    writer_object.writerow(List)
  
    #Close the file object
    f_object.close()

Output:

CSV file After appending List

When you are executing this program Ensure that your CSV file must be closed otherwise this program will give you a permission error.

Append a dictionary as a new row to the existing CSV file

let’s see how to use DictWriter class to append a dictionary as a new row into an existing CSV file. There are several steps to do that.

  • Import DictWriter class from CSV module.
  • Open your CSV file in append mode
    Create a file object for this file.
  • Pass the file object and a list of column names to DictWriter()
    You will get a object of DictWriter.
  • Pass the dictionary as an argument to the Writerow() function of DictWriter
    (it will add a new row to CSV file).
  • Close the file object

Let’s take one Dictionary that we want to add as a new row.

dict={'ID':6,'NAME':'William','RANK':5532,'ARTICLE':1,'COUNTRY':'UAE'}

Now apply the above steps to the program.

Python3




# Import DictWriter class from CSV module
from csv import DictWriter
  
# list of column names 
field_names = ['ID','NAME','RANK',
               'ARTICLE','COUNTRY']
  
# Dictionary
dict={'ID':6,'NAME':'William','RANK':5532,
      'ARTICLE':1,'COUNTRY':'UAE'}
  
# Open your CSV file in append mode
# Create a file object for this file
with open('event.csv', 'a') as f_object:
      
    # Pass the file object and a list 
    # of column names to DictWriter()
    # You will get a object of DictWriter
    dictwriter_object = DictWriter(f_object, fieldnames=field_names)
  
    #Pass the dictionary as an argument to the Writerow()
    dictwriter_object.writerow(dict)
  
    #Close the file object
    f_object.close()

Output:

CSV file after Appending Dictionary

When you are executing this program ensures that your CSV file must be closed otherwise this program will give you a permission error.


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