Problem with my Docker image not running Flask

Question

I am trying to build a Flask docker image. I get the error:

zsh: command not found: flask

I followed this old tutorial to get things working. https://medium.com/@rokinmaharjan/running-a-flask-application-in-docker-80191791e143

In order to just learn how to start flask website with Docker I have made everything simple. My Docker image should just open a Hello world front page.

My example.py:

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
   return 'Hello World'

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

My Dockerfile:

FROM ubuntu:16.04
RUN apt-get update -y
RUN apt-get install python -y
RUN apt-get install python-pip -y
RUN pip install flask
COPY example.py /home/example.py
ENTRYPOINT FLASK_APP=/home/example.py flask run --host=0.0.0.0

I run

sudo docker build . -t flask-app

to build the image.

When I run

docker run -p 8080:5000 flask-app

I get the error:

zsh: command not found: flask

What am I missing here?