CSV file handling in Python – An Intro for Beginners

In this tutorial we will learn about csv file handling in Python .The csv (comma separated values) file is the easiest and simplest way to store any tabular data. The .csv extension is used to save the csv file.

Python has a built-in module csv to work with csv files. So, We need to import the csv module before working on the csv file.

import csv

How to read csv file in Python

There are two methods in csv module to read csv file in Python, one is reader() method and the other is DictReader() method. To read csv file, first we need to open the csv file in “r” (read) mode.

A sample of csv file is given below . We will save it as csv_sample1.csv in the current folder where we are working now . The first row of the given file is the header.

country,capital,type
Abkhazia,Sukhumi,countryCapital
Afghanistan,Kabul,countryCapital
Akrotiri and Dhekelia,Episkopi Cantonment,countryCapital
Albania,Tirana,countryCapital

Python CSV reader() method

The reader() method returns a reader object whose each item is a list, which can be read by iterating each row with the help of for-loop.

Minimal Syntax of reader() method

csv.reader(csvfile)

Parameters of reader() method

csvfile = It is the csv file that we want to read.

Examples of Python CSV reader() method

Example 1: Read csv file in Python using csv.reader() method

import csv
with open("csv_sample1.csv","r",newline="") as csv_file:
    # creating reader object
    csv_reader=csv.reader(csv_file)
    # reading the file
    for row in csv_reader:
        print(row)

['country', 'capital', 'type']
['Abkhazia', 'Sukhumi', 'countryCapital']
['Afghanistan', 'Kabul', 'countryCapital']
['Akrotiri and Dhekelia', 'Episkopi Cantonment', 'countryCapital']
['Albania', 'Tirana', 'countryCapital']

• In the above code the csv module was first imported .
• Then the file “csv_sample1.csv” is opened in “r” mode.
• Then the reader() method returns the reader-object that is stored in the csv_reader variable.
• Then each row is printed by iterating csv_reader with for-loop.

Note :

When we open a csv file, it is a good habit to use newline = "" in the argument .

Python CSV DictReader() method

The DictReader() method returns a DictReader object whose every item is a dictionary, which can be read by iterating each row with the help of for-loop.

Minimal Syntax of DictReader() method

csv.DictReader(csvfile)

Parameters of DictReader() method

csvfile = It is the csv file that we want to read.

Examples of Python CSV DictReader() method

Example 1: Read csv file in Python using csv.DictReader() method

import csv
with open("csv_sample1.csv","r",newline="") as csv_file:
    # creating reader object
    csv_dictReader= csv.DictReader(csv_file)  
    # reading the file 
    for row in csv_dictReader:
        print(row)

{'country': 'Abkhazia', 'capital': 'Sukhumi', 'type': 'countryCapital'}
{'country': 'Afghanistan', 'capital': 'Kabul', 'type': 'countryCapital'}
{'country': 'Akrotiri and Dhekelia', 'capital': 'Episkopi Cantonment', 'type': 'countryCapital'}
{'country': 'Albania', 'capital': 'Tirana', 'type': 'countryCapital'}

• In the above code the csv module was first imported .
• Then the file “csv_sample1.csv” is opened in “r” mode.
• Then the DictReader() method returns the reader object that is stored in the csv_dictReader variable.
• Then each row is printed by iterating csv_dictReader with for-loop.

Although we have five rows with headers in our file but DictReader() method has printed only four lines here. Each line of which is a dictionary. Notice that the key of each dictionary is each element of the header and the value is the corresponding element of that key for each line. Since there is a header and four lines, four dictionaries have been printed.

So, while applying DictReader() method we need to check if there is any header in the file, if there is header then DictReader() method could be applied.

How to write to a csv file in Python

There are two methods in csv module to write to a csv file in Python, one is writer() method and the other is DictWriter() method. To write to a csv file, first we need to open the csv file in “w” (write) or “a” (append) mode.

Python CSV writer() method

The writer() method returns a writer-object that converts a given string into a delimited string. Then we will apply the writerow() and writerows() method to the writer-object to write the delimited string to a csv file.

Minimal Syntax of writer() method

csv.writer(f)

Parameters of writer() method

f = It is the csv file in which we want to write.

Examples of Python CSV writer() method

Example 1: Write to a csv file in Python using writer() method line by line

import csv
with open("csv_sample.csv","w",newline="") as csv_file:
    # creating writer object
    csv_writer=csv.writer(csv_file)
    # writting header into the file
    csv_writer.writerow(['country', 'capital', 'type'])
    # writting rows into the file
    csv_writer.writerow(['Abkhazia', 'Sukhumi', 'countryCapital'])
    csv_writer.writerow(['Afghanistan', 'Kabul', 'countryCapital'])

• In the above code the csv module was first imported
• Then the “csv sample.csv” file is opened in “w” mode.
• Then the writer() method returns the writer object that has been stored in the csv_writer variable.
• Then write to the file using the writerow() method.

In the line csv_writer.writerow (['country', 'capital', 'type']) csv_writer first converts ['country', 'capital', 'type'] to a delimited string . Then write this delimited string to the file using the writerow() method.

Example 2: Write to a csv file in Python using writer() method

import csv
# row list to write all the row
row_list=[['country', 'capital', 'type'],
['Abkhazia', 'Sukhumi', 'countryCapital'],
['Afghanistan', 'Kabul', 'countryCapital'],
['Akrotiri and Dhekelia', 'Episkopi Cantonment', 'countryCapital'],
['Albania', 'Tirana', 'countryCapital']]
with open("csv_sample.csv","w",newline="") as csv_file:
    csv_writer=csv.writer(csv_file)
    csv_writer.writerows(row_list)

In the above code, multiple lines have been written using writerows() method instead of writerow() method.

Python CSV DictWriter() method

The DictWriter() method is used to write to a csv file from a python dictionary.

Minimal Syntax of DictWriter() method

csv.DictWriter(f,fieldnames)

Parameters of DictWriter() method

• f = It is the csv file in which we want to write.
• fieldnames = It is a list so that the headers of the file are given in a specific order.

Examples of Python CSV DictWriter() method

Example 1: Write to a csv file in Python using DictWriter() method

import csv
with open("csv_sample.csv","w",newline="") as csv_file:
    # list of file header or dictionary key
    header=['country', 'capital', 'type']
    # creating writer object
    csv_dictWriter=csv.DictWriter(csv_file,fieldnames=header)
    # writting file header into the file
    csv_dictWriter.writeheader()
    # writting other rows into the file
    csv_dictWriter.writerow({'country': 'Abkhazia', 'capital': 'Sukhumi', 'type': 'countryCapital'})
    csv_dictWriter.writerow({'country': 'Afghanistan', 'capital': 'Kabul', 'type': 'countryCapital'})

• In the above code the csv module was first imported
• Then the “csv sample.csv” file is opened in “w” mode.
• The DictWriter() method then returns the dictwriter object that is stored in the csv_dictWriter variable.
• Then write to the file using the writerow() method.

Note :

The writerows() method also can be used in dictwriter-object like writer-object.

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