Create docker container with the simple flask application

I will try to create a docker container with the simple flask application created some times ago.

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First, I create a shell script for starting the flask application, namely "boot.sh":

boot.sh

#!/bin/sh
export FLASK_APP=simple.py
flask run --host 0.0.0.0

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Second, we need to create a requirements.txt file:

requirements.txt

flask==1.1.1

Actually you can run the following to get the requirements.txt:

pip freeze > requirements.txt

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Third, together with the simple.py file created in the simple flask application, put those 3 files in an "app" directory:

app/

   - boot.sh

   - requirements.txt

   - simple.py

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Forth, create a Docker file outside the app directory:

Dockerfile

FROM python:3.6-alpine
WORKDIR /home/app
COPY app/ ./
RUN chmod +x ./boot.sh
RUN pip install -r requirements.txt
EXPOSE 5000
ENTRYPOINT ["./boot.sh"]

Build the docker image using the Dockerfile:

     docker build -t simple:latest .

Run the docker container with the docker image we just created:

     docker run -d -p 5000:5000 simple:latest

Check "http://localhost:5000" to check the Flask application.

Simple Flask sample

Just wanna to create a very simple Flask application in a single python source file:

simple.py

from flask import Flask

application = Flask("simple")

@application.route("/")

def index():

return "Hello World"

To run this Flask application, run the following:

• export FLASK_APP=simple.py
• flask run

If you want to put this application in a Docker container, you need to bind to 0.0.0.0:

• flask run --host 0.0.0.0

Now, navigate "http://localhost:5000" to see the word "Hello World" displayed on the browser.

Handling table names with underscore ("_") in flask_sqlalchemy / Python

When you create table class using flask_sqlalchemy (the Flask extension for SQLAlchemy), it can maps the modal class to a proper table automatically. This is cool but if you have a table name with underscore (e.g. MY_SAMPLE_TABLE) and you name your model class with the underscore ('_') as usual, you will find SQLAlchemy will map your table name as something the following:

"MY__SAMPLE__TABLE"

Each single underscore (_) with becomes a double underscores (__). This is annoying and you might believe this is a bug, but in fact you can resolve this issues by naming your table class using the PEP8 naming convention, and named your class as:

class MySampleTable(db.Model):
     field_id = db.Column(db.Integer, primary_key = True)
     field_data = db.Column(db.String(200))

The the SQLAlchemy will map the MySampleTable class to table name as "MY_SAMPLE_TABLE" correctly.

For more information about PEP8, click here for details.