Python Flask File Upload Example

Introduction

The tutorial, Python flask file upload example, will show you how to upload single file using Python 3 and Flask technologies. You may also find useful example on file upload on different technologies.

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Prerequisites

Have Python installed in Windows (or Unix)
Pyhton version and Packages
I am using Python 3.6.6 version

Example with Source Code

Please go through the following steps in order to implement Python flask file upload example.

Step 1. Create the below app.py script(py is the extension to indicate Python script) where we import the flask module. Notice how we create flask instance. Here we need to assign secret key otherwise flash will not work in Python.

In the below script we import the required module – Flask. If you do not have this module then install it.

Here we have also specified the file upload folder and maximum size of the file to be uploaded as 16MB.

from flask import Flask

UPLOAD_FOLDER = 'D:/uploads'

app = Flask(__name__)
app.secret_key = "secret key"
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER
app.config['MAX_CONTENT_LENGTH'] = 16 * 1024 * 1024

Step 2. Next we need main.py script. This script is the perfect instance of Python flask file upload example. It defines all required URIs for performing file upload operations.

We have used upload.html page for uploading file to the desired directory.

We show success message on successful file upload.

import os
#import magic
import urllib.request
from app import app
from flask import Flask, flash, request, redirect, render_template
from werkzeug.utils import secure_filename

ALLOWED_EXTENSIONS = set(['txt', 'pdf', 'png', 'jpg', 'jpeg', 'gif'])

def allowed_file(filename):
	return '.' in filename and filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS
	
@app.route('/')
def upload_form():
	return render_template('upload.html')

@app.route('/', methods=['POST'])
def upload_file():
	if request.method == 'POST':
        # check if the post request has the file part
		if 'file' not in request.files:
			flash('No file part')
			return redirect(request.url)
		file = request.files['file']
		if file.filename == '':
			flash('No file selected for uploading')
			return redirect(request.url)
		if file and allowed_file(file.filename):
			filename = secure_filename(file.filename)
			file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
			flash('File successfully uploaded')
			return redirect('/')
		else:
			flash('Allowed file types are txt, pdf, png, jpg, jpeg, gif')
			return redirect(request.url)

if __name__ == "__main__":
    app.run()

Step 3. Now we need template page for uploading file. This is upload.html page kept under subdirectory – templates. You can use this page for uploading single file.

<!doctype html>
<title>Python Flask File Upload Example</title>
<h2>Select a file to upload</h2>
<p>
	{% with messages = get_flashed_messages() %}
	  {% if messages %}
		<ul class=flashes>
		{% for message in messages %}
		  <li>{{ message }}</li>
		{% endfor %}
		</ul>
	  {% endif %}
	{% endwith %}
</p>
<form method="post" action="/" enctype="multipart/form-data">
    <dl>
		<p>
			<input type="file" name="file" autocomplete="off" required>
		</p>
    </dl>
    <p>
		<input type="submit" value="Submit">
	</p>
</form>

Testing of the application

When you open the default URL http://localhost:5000 then you will see below page:

python flask file upload

When you select a file for upload: you can select only the specified types of files as in the main.py script.

python flask file upload

When you click on Submit button after selecting a file or files:

python flask file upload

Now you check the uploaded file in the destination:

python flask file upload

You may like to read Python Flask Multiple Files Upload Example.

Source Code

download source code

That’s all. Thanks for reading.

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25 Thoughts to “Python Flask File Upload Example”

  1. Akshay Jhawar

    Hi Roy,

    Thanks fo sharing the article.
    I am facing an error which says ModuleNotFoundError: No module named ‘app’.

    I have saved the app.py file under the uploads folder. Your article says save it under Flask, but where do I find that?

    1. Hi Akshay, please browse the github link. The same structure you have to follow.

  2. Paulo Ricardo

    Como eu consigo verificar o tamanho do arquivo e a extensão?

  3. KAILASH KOLLURU

    How did you start the local server?

    1. Executing main.py file will start the local server

  4. Paulo Ricardo

    Artigo muito bom, obrigado de certo!

  5. Yurika

    Amazing guide! Is there a way to display the image uploaded on to the page?

    1. Yes it is possible but I don’t have a guide right now

  6. Satyam

    Awesome guide. Helped me a lot

  7. G

    Appreciate your tutorial – sign up for bat so I can support

  8. Arthur Duarte

    Thanks, this article was really useful and straight to the point!

  9. ashwin

    I am facing a 404 issue when the run the code.

  10. mt

    This only works with a HTML form – how can you correct this so you can call it from any external client, ex postman ? if you try from postman request.files always will be 0 len.

    1. You need to build REST API to upload from external clients.

  11. AlucardSama04

    After I uploaded the video, How can I redirect to video url?

    1. Replace return redirect('/') by return redirect('your video url')

  12. TheFiorano

    Hi,
    Thanks for posting this solution. I am trying to create a python web app in VS2019 using this code. I have installed flask and werkzeug but I am getting an error on the import urllib.request (unresolved import ‘urllib.request’) . Do you have any advice on how to resolve this please? Many thanks!

  13. Vas

    Thanks a lot for the detailed instructions. I am getting a 405 error though when submitting the request. Any idea how to resolve this?

    1. 405 means method not allowed. Please check your are posting request through correct http method that is defined on your server side.

  14. sneha

    when i select a pdf file and submit it throws me Internal server error

    1. check what error you get in the browser log

  15. Harsh Purbiya

    this program can be used to upload only single file, how can i upload multiple files.
    the html page provided here, is selecting multiple files but uploading only one.
    help!!!!!!

    1. Thanks for pointing out. Yes this is for uploading single file. I will post soon on how to upload multiple files.

  16. Jeff Kim

    Just wanted to thank you for how bare-bones this tutorial is. Got me exactly what I needed, when I needed it

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