Uploading and Reading a CSV File in Flask

Last Updated : 10 Feb, 2023

Flask is a flexible, lightweight web-development framework built using python. A Flask application is a Python script that runs on a web server, which listens to HTTP requests and returns responses. It is designed for simple and faster development. In this article, let’s upload a CSV (Comma-Separated Values) file and read the contents of the file on a web page of the browser.

Required Module

Install Flask by running the pip command in your terminal. Additionally, you may want to install some popular libraries such as Pandas.

pip install Flask
pip install Pandas

Implementation to Upload and Read the CSV File in Flask Application

Here in this Flask application, we are creating a folder named ‘staticFiles’ to store our uploaded CSV files.

Uploading and Reading a CSV File in Flask

Application File Directory

index.html

Let’s create a user interface (web page) – index.html for uploading the CSV file.

HTML

<!DOCTYPE html>
<html>  
<head>  
    <title>Uploading & Reading CSV file</title>  
</head>  
<body>  
    <form method = "POST" enctype="multipart/form-data" action = "/">    
        <input type="file" name="file" accept=".csv">
        <input type = "submit" value="Upload">  
    </form>
    <p style="color:blue;">Choose csv file to upload</p>
  <form action="/show_data" target="_blank">
        <input type="submit" value="Show CSV"/>
    </form>
</body>  
</html>

Output:

index2.html

To let the user know that the file uploaded successfully we are creating another HTML file – index2.html.

HTML

<!DOCTYPE html>
<html>  
<head>  
    <title>Uploading & Reading CSV file</title>  
</head>  
<body>  
    <form method = "POST" enctype="multipart/form-data" action = "/">    
        <input type="file" name="file" accept=".csv">
        <input type = "submit" value="Upload">  
    </form>
    <p style="color:green;"> File uploaded successfully!! </p>
  <form action="/show_data" target="_blank">
        <input type="submit" value="Show CSV"/>
    </form>
</body>  
</html>

Output:

show_csv_data.html

We are also creating another HTML file – show_csv_data.html for displaying the data after clicking the Show CSV button.

HTML

<!DOCTYPE html>
<html lang="en">
<head>
  </head>
  <body>
    <br>
{{ data_var|safe }}
    </body>
</html>

Output:

Reading CSV file data in Table Format on a web page

app.py

Launch app.py from the code editor first, then open the deployment server URL in a web browser at http://127.0.0.1:5000. A web page with three buttons—Choose a file, Upload, and Show CSV—then appears. Click the Upload button to upload the CSV file. Then a prompt indicating that the file successfully uploaded displays. To read the file data on the website, select the “Show CSV” button. When you select “Show CSV,” a new tab opens up with your file’s data shown in tabular format.

Python3

from distutils.log import debug
from fileinput import filename
import pandas as pd
from flask import *
import os
from werkzeug.utils import secure_filename
 
UPLOAD_FOLDER = os.path.join('staticFiles', 'uploads')
 
# Define allowed files
ALLOWED_EXTENSIONS = {'csv'}
 
app = Flask(__name__)
 
# Configure upload file path flask
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER
 
app.secret_key = 'This is your secret key to utilize session in Flask'
 
 
@app.route('/', methods=['GET', 'POST'])
def uploadFile():
    if request.method == 'POST':
      # upload file flask
        f = request.files.get('file')
 
        # Extracting uploaded file name
        data_filename = secure_filename(f.filename)
 
        f.save(os.path.join(app.config['UPLOAD_FOLDER'],
                            data_filename))
 
        session['uploaded_data_file_path'] =
        os.path.join(app.config['UPLOAD_FOLDER'],
                     data_filename)
 
        return render_template('index2.html')
    return render_template("index.html")
 
 
@app.route('/show_data')
def showData():
    # Uploaded File Path
    data_file_path = session.get('uploaded_data_file_path', None)
    # read csv
    uploaded_df = pd.read_csv(data_file_path,
                              encoding='unicode_escape')
    # Converting to html Table
    uploaded_df_html = uploaded_df.to_html()
    return render_template('show_csv_data.html',
                           data_var=uploaded_df_html)
 
 
if __name__ == '__main__':
    app.run(debug=True)