{"id":743,"date":"2020-10-24T09:10:51","date_gmt":"2020-10-24T09:10:51","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=743"},"modified":"2025-03-30T12:12:20","modified_gmt":"2025-03-30T12:12:20","slug":"python-read-csv-file","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-basics\/python-read-csv-file\/","title":{"rendered":"Python Read CSV File"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to read a CSV file in Python using the built-in csv<\/code> module.<\/p>\n\n\n\n

What is a CSV file #<\/a><\/h2>\n\n\n\n

CSV stands for comma-separated values. A CSV file is a delimited text file that uses a comma to separate values.<\/p>\n\n\n\n

A CSV file consists of one or more lines. Each line is a data record. And each data record consists of one or more values separated by commas. In addition, all the lines of a CSV file have the same number of values.<\/p>\n\n\n\n

Typically, you use a CSV file to store tabular data in plain text. The CSV file format is quite popular and supported by many software applications such as Microsoft Excel and Google Spreadsheet.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Reading a csv file in Python #<\/a><\/h2>\n\n\n\n

To read a CSV file in Python, you follow these steps:<\/p>\n\n\n\n

First, import the csv module:<\/p>\n\n\n

import<\/span> csv<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, open the CSV file using the built-in open() function in the read mode:<\/p>\n\n\n
f = open('path\/to\/csv_file'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
If the CSV contains UTF8 characters, you need to specify the encoding like this:<\/p>\n\n\n
f = open('path\/to\/csv_file'<\/span>, encoding='UTF8'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, pass the file object (f<\/code>) to the reader()<\/code> function of the csv<\/code> module. The reader()<\/code> function returns a csv reader object:<\/p>\n\n\n
csv_reader = csv.reader(f)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
for<\/span> line in<\/span> csv_reader:\n    print(line)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
For example, the following accesses the first value of a particular line:<\/p>\n\n\n
line[0<\/span>]<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Finally, always close the file once you’re no longer access it by calling the close()<\/code> method of the file object:<\/p>\n\n\n
f.close()    <\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
It’ll be easier to use the with<\/code> statement so that you don’t need to explicitly call the close()<\/code> method.<\/p>\n\n\n\n
The following illustrates all the steps for reading a CSV file:<\/p>\n\n\n
import<\/span> csv\n\nwith<\/span> open('path\/to\/csv_file'<\/span>, 'r'<\/span>) as<\/span> f:\n    csv_reader = csv.reader(f)\n    for<\/span> line in<\/span> csv_reader:\n        # process each line<\/span>\n        print(line)\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Reading a CSV file examples #<\/a><\/h2>\n\n\n\n
We’ll use the country.csv<\/code> file that contains country information including name, area, 2-letter country code, 3-letter country code:<\/p>\n\n\n\n
\"Python<\/figure>\n\n\n\nDownload country.csv file<\/a>\n\n\n\n
The following shows how to read the country.csv<\/code> file and display each line to the screen:<\/p>\n\n\n
import<\/span> csv\n\nwith<\/span> open('country.csv'<\/span>, encoding=\"utf8\"<\/span>) as<\/span> f:\n    csv_reader = csv.reader(f)\n    for<\/span> line in<\/span> csv_reader:\n        print(line)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
['name'<\/span>, 'area'<\/span>, 'country_code2'<\/span>, 'country_code3'<\/span>]\n['Afghanistan'<\/span>, '652090.00'<\/span>, 'AF'<\/span>, 'AFG'<\/span>]\n['Albania'<\/span>, '28748.00'<\/span>, 'AL'<\/span>, 'ALB'<\/span>]\n['Algeria'<\/span>, '2381741.00'<\/span>, 'DZ'<\/span>, 'DZA'<\/span>]\n['American Samoa'<\/span>, '199.00'<\/span>, 'AS'<\/span>, 'ASM'<\/span>]\n...\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The country.csv<\/code> has the first line as the header. To separate the header and data, you use the enumerate()<\/code> function to get the index of each line:<\/p>\n\n\n
import<\/span> csv\n\nwith<\/span> open('country.csv'<\/span>, encoding=\"utf8\"<\/span>) as<\/span> f:\n    csv_reader = csv.reader(f)\n    for<\/span> line_no, line in<\/span> enumerate(csv_reader, 1<\/span>):\n        if<\/span> line_no == 1<\/span>:\n            print('Header:'<\/span>)\n            print(line)  # header<\/span>\n            print('Data:'<\/span>)\n        else<\/span>:\n            print(line)  # data<\/span>\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we use the enumerate()<\/code> function and specify the index of the first line as 1.<\/p>\n\n\n\n
Inside the loop, if the line_no<\/code> is 1, the line is the header. Otherwise, it’s a data line.<\/p>\n\n\n\n
Another way to skip the header is to use the next()<\/code> function. The next()<\/code> function forwards to the reader to the next line. For example:<\/p>\n\n\n
import<\/span> csv\n\nwith<\/span> open('country.csv'<\/span>, encoding=\"utf8\"<\/span>) as<\/span> f:\n    csv_reader = csv.reader(f)\n\n    # skip the first row<\/span>\n    next(csv_reader)\n\n    # show the data<\/span>\n    for<\/span> line in<\/span> csv_reader:\n        print(line)\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The following reads the country.csv<\/code> file and calculate the total areas of all countries:<\/p>\n\n\n
import<\/span> csv\n\ntotal_area = 0<\/span>\n\n# calculate the total area of all countries<\/span>\n\nwith<\/span> open('country.csv'<\/span>, encoding=\"utf8\"<\/span>) as<\/span> f:\n    csv_reader = csv.reader(f)\n\n    # skip the header<\/span>\n    next(csv_reader)\n\n    # calculate total<\/span>\n    for<\/span> line in<\/span> csv_reader:\n        total_area += float(line[1<\/span>])\n\nprint(total_area)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
148956306.9<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Reading a CSV file using the DictReader class #<\/a><\/h2>\n\n\n\n
When you use the csv.reader()<\/code> function, you can access values of the CSV file using the bracket notation such as line[0]<\/code>, line[1]<\/code>, and so on. However, using the csv.reader()<\/code> function has two main limitations:<\/p>\n\n\n\n
Each line is a list<\/a> of values. To access each value, you use the square bracket notation []<\/code>. The first value has an index of 0. The second value has an index of 1, and so on.<\/p>\n\n\n\n
The csv_reader<\/code> is an iterable<\/a> object of lines from the CSV file. Therefore, you can iterate over the lines of the CSV file using a for<\/code> loop:<\/p>\n\n\n