uploader

Ensure you create an upload folder destination in the static directory:

imageUploader.py

from flask import *
import os, sys
app = Flask(__name__)

folderLocation = os.path.dirname(os.path.realpath(sys.argv[0]))
app.config["uploadFolder"] = folderLocation + "/static/uploads/"

imagePage = '''
<form action="/upload" method="post" enctype="multipart/form-data">
  <input type="file" name="fileToUpload" id="fileToUpload"><br>
  <input type="submit" value="upload file" name="submit">
</form><br>
{% for eachImage in imageList %}
  <img src="{{ url_for("static", filename="uploads/"+eachImage) }}"><br>
{% endfor %}
'''

@app.route("/upload", methods=["POST"])
def upload():
    file = request.files["fileToUpload"]
    file.save(os.path.join(app.config["uploadFolder"],file.filename))
    return redirect("/")

@app.route("/")
def start():
    return render_template_string(imagePage, imageList=getImages())

def getImages():
    dirListing = os.listdir(app.config["uploadFolder"])
    imageList = []
    for file in dirListing:
        imageList.append(file)
    return imageList

app.run(debug=True)

imageUploader.py

from flask import *
import os, sys
app = Flask(__name__)

folderLocation = os.path.dirname(os.path.realpath(sys.argv[0]))
app.config["uploadFolder"] = folderLocation + "/static/uploads/"

fileUploader = '''
<form action="/upload" method="post" enctype="multipart/form-data">
  <input type="file" name="fileToUpload" id="fileToUpload"><br>
  <input type="submit" value="upload file" name="submit">
</form>
'''

@app.route("/upload", methods=["POST"])
def upload():
    file = request.files["fileToUpload"]
    file.save(os.path.join(app.config["uploadFolder"],file.filename))
    return redirect("/")

@app.route("/")
def start():
    return render_template_string(fileUploader)

app.run(debug=True)