app.py

import os
from flask import Flask, flash, request, redirect, url_for, render_template
from werkzeug.utils import secure_filename
import uuid 


UPLOAD_FOLDER = 'tmp/'
ALLOWED_EXTENSIONS = set(['png', 'jpg', 'jpeg', 'gif'])

app = Flask(__name__)
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER
app.secret_key = "super secret key"

def allowed_file(filename):
    return '.' in filename and filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS

@app.route('/', methods=['GET', '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 user does not select file, browser also submit an empty part without filename
    if file.filename == '':
      flash('No selected file')
      return redirect(request.url)
    if file and allowed_file(file.filename):
      filename = secure_filename(file.filename)
      filename =  str(uuid.uuid4()) + "." + filename.split('.')[1]
      file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
      return redirect(url_for('upload_file', filename=filename))
  return render_template("home.html") 

if __name__ == '__main__':
  app.run(debug=True)