Upload Multiple Files In Python Flask (Simple Example)

Welcome to a tutorial on how to upload multiple files in Python Flask. So you need to upload multiple files in Flask, but have no idea how to get started? Here is a quick sharing and simple example – Read on!

 

 

TABLE OF CONTENTS

 

 

EXAMPLE CODE DOWNLOAD

Source code on GitHub Gist

Just click on “download zip” or do a git clone. I have released it under the MIT license, so feel free to build on top of it or use it in your own project.

 

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QUICK SETUP

• Create a virtual environment virtualenv venv and activate it – venv\Scripts\activate (Windows) venv/bin/activate (Linux/Mac)
• Install required libraries – pip install flask werkzeug
• For those who are new, the default Flask folders are –
  • static Public files (JS/CSS/images/videos/audio)
  • templates HTML pages

 

 

STEP 1) HTML UPLOAD FORM

<form action="http://localhost/upload" method="POST" enctype="multipart/form-data">
  <input type="file" name="file" multiple required>
  <input type="submit" value="Upload!">
</form>

First, we start with an HTML file upload form. I don’t think this needs any explanation, it is just a <input type="file"> field that accepts multiple files.

 

STEP 2) FLASK SERVER

2A) INIT

# (A) INIT
# (A1) LOAD MODULES
from flask import Flask, render_template, request
from werkzeug.utils import secure_filename
 
# (A2) FLASK SETTINGS + INIT
app = Flask(__name__)
HOST_NAME = "localhost"
HOST_PORT = 80
app.config["UPLOAD_FOLDER"] = "uploads/"
# app.debug = True

This section of the Flask server script should be self-explanatory too. We are just loading the required modules and defining a bunch of settings here.

 

 

2B) HTTP ROUTES

# (B) HTML UPLOAD PAGE
@app.route("/")
  def index():
  return render_template("S1_upload.html")
 
# (C) UPLOAD HANDLER
@app.route("/upload", methods = ["POST"])
def save_upload():
 files = request.files.getlist("file")
  # print(files)
  for f in files:
    filename = secure_filename(f.filename)
    f.save(app.config["UPLOAD_FOLDER"] + filename)
  return "UPLOAD OK"

Next, we define 2 “pages”.

• / To serve the HTML file upload form.
• /upload To handle the upload itself.
  • Use files = request.files.getlist("file") to get all of the uploaded files.
  • Then loop through the files for f in files.
  • Save them onto the server f.save().

 

2C) START

# (D) START
if __name__ == "__main__":
  app.run(HOST_NAME, HOST_PORT)

Captain Obvious at your service. Start the Flask HTTP server.

 

 

 

RESTRICTING FILE TYPES

HTML UPLOAD FORM

<form action="http://localhost/upload" method="POST" enctype="multipart/form-data">
  <input type="file" name="file" required multiple accept="image/*">
  <input type="submit" value="Upload!">
</form>

To restrict the accepted file types, the quick and easy way is to add a accept="MIME TYPE" on the <input type="file"> itself.

 

FLASK SERVER

# DEFINE ALLOWED EXTENSIONS
ALLOWED_EXTENSIONS = {"txt", "pdf", "png", "jpg", "jpeg", "gif"}
 
# FUNCTION TO CHECK FILENAME
def allowed_file(filename):
  return "." in filename and \
    filename.rsplit(".", 1)[1].lower() in ALLOWED_EXTENSIONS
 
# SAVE UPLOAD ONLY IF ALLOWED EXTENSION
if allowed_file(f.filename):
  filename = secure_filename(f.filename)
  f.save(app.config["UPLOAD_FOLDER"] + filename)

But the HTML file type restriction can be easily messed with, code ninjas can just change it in the developer’s console. So it’s safer to also include the file type check in Python itself, before we proceed to save the file on the server.

 

LINKS & REFERENCES

• Python Flask
• Uploading Files In Flask