Dockerized Python Development

First, get docker. If you are on a Mac and do not have an XCode, you will need to install that first from the App Store.  The download and install may be lengthy, it took about 15 min for me
After docker installation, you should have a docker-compose utility installed, check that by running docker-compose
which should not error out and look somewhat like this:

$ docker-compose
Define and run multi-container applications with Docker.

Usage:
  docker-compose [-f <arg>...] [options] [--] [COMMAND] [ARGS...]
  docker-compose -h|--help

...

This is what my directory structure looks like:

├──Dockerfile                   defines how to build docker image
├──requirements.txt             requirements file
├──docker-compose.yml           defines how to run the docker image
└──src/                         application code           
    └── flask_app.py            the flask server

 
​
flask_app.py

from flask import Flask, jsonify, request, abort

app=Flask(__name__)

data=[{'fname':'Steve', 'lname':'Jobbs'},{'fname':'Bill', 'lname':'Gates'}]

@app.route('/createperson', methods=['POST'])
def create_person():
	print(request.json)
	if not request.json or not 'person' in request.json:
		abort(400)
	data.append(request.json['person'])
	return jsonify({'data' : data}), 201

@app.route('/data', methods=['GET'])
def get_data():
	return jsonify({'data' : data})

@app.route('/data/', methods=['GET'])
def get_data_byid(id):
	return jsonify({'data' : data[id]})

if __name__ == "__main__":
	app.run(host='0.0.0.0', port=5000)

​
requirements.txt

flask == 1.1.2
markupsafe >=1.0,<2.0

Following file defines how the docker image should be built
Dockerfile

# which base image we will use for the container
#https://hub.docker.com/search?type=image&category=base
FROM python:3.8

# your container will have some folders/files already installed
#this line creates a new folder at the root of the container
#that will be used as a work directory
#after the working directory is created, assume you are inside it
WORKDIR /code

# copy the dependencies file to the working directory
COPY requirements.txt .

# install dependencies
RUN pip install -r requirements.txt

# copy the content of the local src directory to the working directory
COPY src/ .

# command to run on container start
CMD [ "python", "./flask_app.py" ]

​Following file tells Docker how to run your application
docker-compose.yml

# build from Dockerfile
version: "3.8"
services:
  web:
    #build from Dockerfile in the current directory
    build: .
    ports:
      # host:container = 127.0.0.1:5000 in your browser will map to 500 in container
      - "127.0.0.1:5000:5000" 

Now we can build our image:

$ docker-compose build
Building web
Step 1/6 : FROM python:3.8
 ---> 9756fa8d7b9d
Step 2/6 : WORKDIR /code
 ---> Running in 7917f6eb3663
Removing intermediate container 7917f6eb3663
 ---> 41fe8bff45d7
Step 3/6 : COPY requirements.txt .
 ---> d9b9e9eac29f
Step 4/6 : RUN pip install -r requirements.txt
 ---> Running in 9cddfd6b1864
Collecting flask==1.1.2
  Downloading Flask-1.1.2-py2.py3-none-any.whl (94 kB)
Collecting markupsafe<2.0,>=1.0
  Downloading MarkupSafe-1.1.1-cp38-cp38-manylinux1_x86_64.whl (32 kB)
Collecting itsdangerous>=0.24
  Downloading itsdangerous-1.1.0-py2.py3-none-any.whl (16 kB)
Collecting Jinja2>=2.10.1
  Downloading Jinja2-2.11.2-py2.py3-none-any.whl (125 kB)
Collecting click>=5.1
  Downloading click-7.1.2-py2.py3-none-any.whl (82 kB)
Collecting Werkzeug>=0.15
  Downloading Werkzeug-1.0.1-py2.py3-none-any.whl (298 kB)
Installing collected packages: itsdangerous, markupsafe, Jinja2, click, Werkzeug, flask
Successfully installed Jinja2-2.11.2 Werkzeug-1.0.1 click-7.1.2 flask-1.1.2 itsdangerous-1.1.0 markupsafe-1.1.1
Removing intermediate container 9cddfd6b1864
 ---> bf8e35ceea43
Step 5/6 : COPY src/ .
 ---> a58f689d48c6
Step 6/6 : CMD [ "python", "./flask_app.py" ]
 ---> Running in d216702be611
Removing intermediate container d216702be611
 ---> 729c92da104c

Successfully built 729c92da104c
Successfully tagged docker_app_web:latest

If you have the docker dashboard open you will see the new image appear - docker_app_web

Now you can run your image  using following command:
docker-compose up

$ docker-compose up
Creating network "docker_app_default" with the default driver
Creating docker_app_web_1 ... done
Attaching to docker_app_web_1
web_1  |  * Serving Flask app "flask_app" (lazy loading)
web_1  |  * Environment: production
web_1  |    WARNING: This is a development server. Do not use it in a production deployment.
web_1  |    Use a production WSGI server instead.
web_1  |  * Debug mode: off
web_1  |  * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
web_1  | 172.19.0.1 - - [07/Nov/2020 08:18:30] "GET /data HTTP/1.1" 200 -

And you should be able to access the app from your browser

Dockerfile cheatsheet
​docker compose cheatsheet