Develop Reference

Trying to run a python file in flask

I am trying to learn flask. I created a venv and installed flask. I set the flaskblog.py as FLASK_APP. But it says serving flask app 'app.py' and it fails. why is this?
I'm not sure if the image is visible. So, I'll write what I've tried below,
In the windows powershell, I cd to the directory where my venv and python script is, then
$ . vnev\Scripts\activate
$ pip install flask
$ set FLASK_APP=flaskblog.py
$ flask run
it gives me the error saying,
Serving Flask app 'app.py' (lazy loading)
Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
Debug mode: off
Usage: flask run [OPTIONS]
Try 'flask run --help' for help.
Error: Could not import 'app'.
What is wrong here? I have also tried $ setx FLASK_APP "flaskblog.py and still get the same result. I think i created this app.py using pycharm's virtual environment and now, I cannot set other files to FLASK_APP.
What should I do?

WSL2 Docker Flask container doesn't connects

I'm trying to create a simple web application container within Ubuntu-WSL2 with the help of the Docker. So I've built my container creating my-simple-webapp folder and within that folder, I've created Dockerfile and app.py files;
Dockerfile
FROM ubuntu:16.04
RUN apt-get update && apt-get install -y python python-pip
RUN pip install flask
COPY app.py /opt/
ENTRYPOINT FLASK_APP=/opt/app.py flask run --host=0.0.0.0 --port=8080
app.py
import os
from flask import Flask
app = Flask(__name__)
#app.route("/")
def main():
return "Welcome!"
#app.route('/how are you')
def hello():
return 'I am good, how about you?'
if __name__ == "__main__":
app.run(host="0.0.0.0", port=8080)
When I run the command docker build ./my-simple-webapp it works without error. However when I use my browser to connect my container typing 172.17.0.2:8080, o.o.o.o:8080 or localhost:8080 connection times out.
Resource : https://github.com/mmumshad/simple-webapp-flask

If all you run is docker build... then you still need to start your container with docker run....
You can open the docker dashboard (in your Windows tray) to see if your container is actually running.

To actually run your app you need to start a container. First, build the image:
docker build -t simple-webapp-flask .
Then start a container using the image, with 8080:8080 mapping from container to your host:
docker run -p 8080:8080 simple-webapp-flask

If you want to deploy your flask application, you need to choose from the following options:
https://flask.palletsprojects.com/en/1.1.x/deploying/
The way you are trying to do it, can be used only for development purposes.

Running Flask in Docker Using Volumes Causes Error on Reload

I'm setting up my dev environment for a flask app in a docker container and during dev I want to be able to put Flask in development mode so that I can get live reloads when I change a file. I'm using volumes so that I can edit the files outside of docker. I am getting the desired behavior from Flask, on editing the flask test file it detects the file change, however, it appears to be attempting to serve trunkated files instead of the files as edited resulting in errors from the app.
Dockerfile:
FROM python:3.8.1-alpine3.11
RUN apk update && apk upgrade && apk add bash
#Set ENV Variables
ENV FLASK_APP hello.py
#Add user.
RUN adduser -D eskimotv
USER eskimotv
#Set Work directory
WORKDIR /home/eskimotv
#Install Dependencies
COPY requirements requirements
RUN python -m venv venv
RUN venv/bin/pip install --upgrade pip
RUN venv/bin/pip install -r requirements/docker.txt
#Copy project files
COPY frontend frontend
COPY migrations migrations
COPY boot.sh ./
#Deploy Project
EXPOSE 5000
#ENTRYPOINT ["./boot.sh"]
Docker-compose.yml:
version: '3'
services:
frontend:
image: bentsea/eskimotv-frontend:latest
build:
dockerfile: frontend.dockerfile
context: .
ports:
- "8000:5000"
env_file: .env
volumes:
- './boot.sh:/home/eskimotv/boot.sh'
- './hello.py:/home/eskimotv/hello.py'
- './frontend:/home/eskimotv/frontend'
#entrypoint: ./boot.sh
restart: always
Simple flask app, hello.py:
from flask import Flask
app = Flask(__name__)
#app.route('/')
def index():
return '<h1>Hello World!</h1><p> Please work!</p>'
#app.route('/user/<name>')
def user(name):
return '<h1>Hello, {}!</h1>'.format(name)
Environtment variable FLASK_ENV is set to development. When starting up the app for the first time all my changes are displayed correctly:
If I make a very simple edit, such as changing line 10 of hello.py with a cosmetic change, such as the following:
return '<h1>Hello, {}, I made a small change to the text!</h1>'.format(name)
Flask will appropriately reload:
* Detected change in '/home/eskimotv/hello.py', reloading
* Restarting with stat
* Debugger is active!
* Debugger PIN: 234-654-899
172.21.0.1 - - [31/Dec/2019 20:00:20] "GET /user/David HTTP/1.1" 200 -
* Detected change in '/home/eskimotv/hello.py', reloading
* Restarting with stat
* Debugger is active!
* Debugger PIN: 234-654-899
However, the page will begin to produce an error rather than correctly display the page:
Sometimes it's just an EOL error that indicates that the file is truncated, sometimes it indicates this null error. Either restarting the Flask server or undoing the edits made to the file resolves the issue and the app will function normally. Restarting the server every time I make an edit is the action I was wanting to avoid.
Does anyone have any ideas what would cause the files in this volume configuration to load incorrectly and what I can do to resolve the issue to get the intended behavior of having the reload display the file as it is edited?

I don't know why the error is occurring, however it does appear to be caused by mounting a single file instead of a directory. By restructuring my app to mount only entire directories that include the files that need to be updated I was able to successfully use a workflow that allows for automatic Flask reload through Docker on file change.
For whatever reason Docker does not accurately update individual files that are mounted if they are outside of a mounted directory.

Try after you change your code to rebuild your docker.
Before making the change do
docker-compose stop
Then make the change by editing the line
return '<h1>Hello, {}, I made a small change to the text!</h1>'.format(name)
after making your change above, now do
docker-compose build
And finally
docker-compose up

Containerized flask app does not load if port is Changed

I have created a simple flask app that is running on a this is the skeleton o the flask app, which by default runs at port 5000:
# Create the application instance
app = connexion.App(__name__, specification_dir="./")
# read the swagger.yml file to configure the endpoints
app.add_api("swagger.yml")
# Create a URL route in our application for "/"
#app.route("/")
def home():
"""
This function just responds to the browser URL
localhost:5000/
:return: the rendered template "home.html"
"""
return render_template("home.html")
if __name__ == "__main__":
app.run(debug=True)
In the Dockerfile I'm exposing the same port:
RUN python3 -m pip install -r requirements.txt
COPY . /app
EXPOSE 5000
Then I run the container as:
sudo docker run -d -p 5000:5000 my_app:latest
and once the container is up, I'm able to acces to app at:
http://localhost:5000
Now, I'm trying to change to port 5100, for that I'm changing:
a) In the Dockerfile:
COPY . /app
EXPOSE 5100
...
b) When I run the container:
sudo docker run -d -p 5100:5100 my_app:latest
But when I try to visit: http://localhost:5100/
The app is not running there
When I do Docker ps this is shown:
EDIT:
I tried changing the flask app:
app.run(host='0.0.0.0', port=5100)
Still not working, this is the screenshot from docker ps:
Not sure if the error is because still says 5000: at the begining:
5000/tcp, 0.0.0.0:5100->5100/tcp romantic_fermi
This is what I get from docker logs...
* Serving Flask app "server" (lazy loading)
* Environment: production
WARNING: Do not use the development server in a production environment.
Use a production WSGI server instead.
* Debug mode: on
* Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)

You could technically change the default port assigned to the Flask object, but it's simpler to just change the docker mapping.
When you run a command like this:
$ docker run -d -p 5100:5100 my_app:latest
You are saying that you want to forward a port from inside the container (on the right) to your host machine (on the left).
# Left side is your host machine
# Right side is inside of the container
5100:5100
So you could update your run to map to 5000 inside of the container:
$ docker run -d -p 5100:5000 my_app:latest
Then you'll be able to access via http://localhost:5100
PS: If you haven't used docker-compose before, I would highly recommend setting it up after you've worked through this issue. It'll make your life easier in general.

On your .py script ou need to set 5100 port with:
app.run(debug=True,host='0.0.0.0', port=5100)
Everything else you did is correct!
If still your python are listening on port 5000, probably it's the old version.

flask.cli.NoAppException: The file/path provided (new_app.py) does not appear to exist

I keep getting this error flask.cli.NoAppException: The file/path provided (new_app.py) does not appear to exist. Please verify the path is correct. If app is not on PYTHONPATH, ensure the extension is .py it goes away after I restart the Flask server.
I am running flask run in the correct directory where my app is. This just started happening after working for 2 weeks. I've read that it could be due to an import error, but I am not finding any modules that are not installed on my virutalenv.
from flask import Flask
app = Flask(__name__)
app.debug=True

Most likely you haven't set the FLASK_APP environment variable.
To run the application you can either use the flask command or
python’s -m switch with Flask. Before you can do that you need to tell
your terminal the application to work with by exporting the FLASK_APP
environment variable:
$ export FLASK_APP=hello.py
$ flask run * Running on http://127.0.0.1:5000/
If you are on Windows you need to use set
instead of export.
Alternatively you can use python -m flask:
$ export FLASK_APP=hello.py
$ python -m flask run * Running on http://127.0.0.1:5000/
EDIT
If you have FLASK_APP set then try adding this to new_app.py
app.run(debug=True, port=8800)
Or if you're on Windows:
if __name__ == '__main__':
app.run(debug=True, port=8800)
And then just execute the app with python new_app.py.