Introduction
The tutorial, Python flask file upload example, will show you how to upload single file using Python 3 and Flask web framework. You may also find useful example on file upload on different technologies.
In this file upload example I am going to show you how to select single file and upload in the server.
Related Posts:
- Python Flask REST API File Upload Example
- Python Flask Multiple Files Upload Example
- Python Flask REST API Multiple Files Upload
Prerequisites
Python 3.6.6 – 3.9.1, Flask 1.1.1 – 1.1.2 (pip install flask
)
Project Directory
Create a project root directory called python-flask-file-upload as per your chosen location.
I may not mention the project’s root directory name in the subsequent sections but I will assume that I am creating files with respect to the project’s root directory.
App Configuration
Create the below app.py script(py is the extension to indicate Python script) where I need to import the flask module. Notice how I create flask instance. Here I need to assign a secret key otherwise flash will not work in Python.
In the below script I import the required module – Flask. If you do not have this module then install it using the command pip install flask
.
Here I 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
File Upload
Next I create 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.
I have used upload.html page for uploading file to the desired directory. In the next section I will talk about this template file – upload.html.
I 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()
Template File – UI
Now I need a template page for uploading file. This is upload.html page kept under subdirectory – templates. This templates directory is the standard folder in the flask based web application. 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>
Deploying the Application
Now navigate to the project’s root directory using command line tool and execute the command python main.py
or simple main.py
, your server will be started on default port 5000.
If you want to change the port then you can change the line app.run()
to app.run(port=5001)
, where 5001 is the new port.
Testing the Application
When you open the default URL http://localhost:5000 then you will see below page:
When you select a file for upload: you can select only the specified types of files as in the main.py script.
When you click on Submit button after selecting a file or files:
Now you check the uploaded file in the destination:

That’s all about file upload example using Python and Flask.
Awesome guide. Helped me a lot