FLASK WEB DEVELOPMENT

Web development In Python

So one of the application domains of Python is Web development. You can use it to make powerful and fast web applications. In so making, a number of tools and frameworks have been developed to aid web development in Python.

Some of these are but not limited to;

Django
Flask
Pyramid

web-frameworks-python

Our focus will be on the Flask framework.
And for a quick overview on how to get started with Python Web development, consider looking into, Getting Started with Python Web Development using ###FLASK

Once you have mastered the basic overview of flask, we will dive into the topic of the day.
What an introduction !!! Hope you are enjoying the article. Let us refocus now.

refocus-image

Given a minimal Flask application, such as;

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello World, dear Friend!'


@app.route('/page/<int:page_num>')
def content(page_num):
    return f'<h1>Yoo.. It is your page {page_num}</h1>'

`if __name__ == '__main__':
    app.run(host='',port='',debug=True)

The minimal application can be run following the steps below, (as you might be familiar),

On Bash

export FLASK_APP=app.py
flask run

Other scenarios you might want to specify the host and port number, environment, debug mode etc. for which you want your flask application to run, you would have to include all that into the export command above.
That can become tedious over time as you develop your cool project, pressing up arrow key many times to retrace the export command (bash users, you know what I mean).

On Bash
flask run

The variables that we add to the export command are known as environment variables. These variables are used by your flask application to serve your project.

Examples of environment variables include;

FLASK_ENV
FLASK_DEBUG.
FLASK_RUN_EXTRA_FILES
FLASK_RUN_HOST
FLASK_RUN_PORT
FLASK_RUN_CERT
FLASK_RUN_KEY

Those are default flask environment variables defined by the framework. If not specified, they use their default values.

User defined variables
Also, if you wanted to connect your application to a database, you would have to hard code your credentials into your python code, which is not recommended.
An example

from flask import Flask
app = Flask(__name__)

app.config[MYSQL_USER]="your_username"
app.config[MYSQL_HOST]="localhost"
app.config[MYSQL_DB]="my_appdb"
app.config[MYSQL_PASSWORD]="your_password"

@app.route('/')
def index():
    return {'Message': 'Hello World'}

That kind of hard coding credentials is not ideal if you are working on a large project with other people

Incase you do not follow Strict password policies and use one password everywhere....You are hacked!!!. You just shared your password with the world.

So how do we deal with the flask environment variables?
We are going to see how to load flask environment variables automatically. You are here because you're tired of setting environment variables every time you are running your flask app? Variables like FLASK_APP or FLASK_ENV using export command. Am going to help you do just that.

Step 1: Install python-dotenv
In your virtual environment, run;
pip install python-dotenv

I emphasize, always use virtual environments on your system to prevent corrupting your main Python installation. In case you want a recap on how to create virtual environments, refer to this guide. Creation of Virtual Environments

Step 2: Create .env and .flaskenv files in your project root folder

On Bash

touch .env
touch .flaskenv

Step 3: Place your flask environment variables in .flaskenv
Depending on your use case, this will guide you on what to include.

In .flaskenv

//this is the .flaskenv file
FLASK_ENV - Controls the environment.
FLASK_DEBUG - Enables debug mode.
FLASK_RUN_EXTRA_FILES - A list of files that will be watched by the re-loader in addition to the Python modules.
FLASK_RUN_HOST - The host you want to bind your app to.
FLASK_RUN_PORT - The port you want to use.
FLASK_RUN_CERT - A certificate file for so your app can be run with HTTPS.
FLASK_RUN_KEY - The key file for your cert.
for example; FLASK_APP=app.py

Boom, great work done. To run your app now, Simply do run;

flask-run

That was fast,.... right?? Yes so you can now focus on programming instead of looking for which flask environment variable is missing.

So how about my-secretly-defined environment variables?
Yes getting to that now. Follow this guide.

Step 1. Place your-secretly-defined environment variables in .env
These can include;

Login credentials to the database
API keys
SECRET_KEY (among others)

In .env
//This is the .env file
MYSQL_USER=root
MYSQL_PASSWORD=my_mysql_password
MYSQL_DB=userdb
MYSQL_HOST=localhost
SECRET_KEY=topsecretkey
API_KEY=donotsharethisapikeywithanyone

Step 2: Create a settings.py file
(Since these variables are not served automatically, we have to load them through this settings.py file)

In settings.py
//This is the settings.py file

from os import environ
SECRET_KEY=environ.get('SECRET_KEY)
API_KEY=environ.get('API_KEY')
MYSQL_USER=environ.get('MYSQL_USER')
//add any more variables you have

Note: For consistency, it is good to keep the same variable name as the environment variable.

Step 3: Add the configurations to our app
In your app.py , the file that has your flask object.
app.config.from_pyfile('settings.py')

loading all environment variables from settings.py

So what happens is that the settings.py will read the values you placed in your .env file and store them in variables as you defined them in settings.py.

When you use the flask object's config method, together with the from_pyfile sub-method, the app will have access to the secretly defined variables in a secure way.

Good lck in coding