Summary of some techniques for deeply customizing Python's Flask framework development environment

Flask environment configuration
Your application may require a large number of packages to work properly. If you don't need the Flask package, you may have read the wrong tutorial. Your application's environment is basically the foundation for everything that happens when your application is running. We are lucky because there are many ways in which we can easily manage our environment.
Use virtualenv to manage your environment
virtualenv is a tool for isolating your applications in so-called virtual environments. A virtual environment is a directory that contains software that your application depends on. A virtual environment can also change your environment variables to maintain the environment variables contained in your development environment. Instead of downloading packages, like Flask, into your system-level or user-level packages directory, we can download them into a separate directory that is only used by our application. This makes it easy to specify the version of Python used and the packages each project depends on.
Virtualenv also allows you to use different versions of the same package in different projects. This flexibility can be important if you are using an older system and have several projects on it that require different versions.
When using virtualenv, you usually only need to install a few Python packages on your system. One of them is virtualenv itself. You can use Pip to install virtualenv packages.
Once virtualenv is installed on your system, you can start creating virtual environments. Go to the directory where your project is located and run the virtualenv command. It requires one parameter, which is the target directory of the virtual environment. Here's an overview of what it looks like.

$ virtualenv venv
New python executable in venv/bin/python
Installing Setuptools...........[...].....done.
Installing Pip..................[...].....done.

$ which python
/usr/local/bin/python
$ source venv/bin/activate
(venv)$ which python
/Users/robert/Code/myapp/venv/bin/python

(venv)$ deactivate

$ mkvirtualenv rocket
New python executable in rocket/bin/python
Installing setuptools...........[...].....done.
Installing pip..................[...].....done.
(rocket)$

(rocket)$ pip freeze > requirements.txt
$ workon fresh-env
(fresh-env)$ pip install -r requirements.txt
[...]
Successfully installed flask Werkzeug Jinja2 itsdangerous markupsafe
Cleaning up...
(fresh-env)$

*.pyc
instance/

DEBUG = True # Turns on debugging features in Flask
BCRYPT_LEVEL = 12 # Configuration for the Flask-Bcrypt extension
MAIL_FROM_EMAIL = "robert@example.com" # For use in application emails

# app.py or app/__init__.pyfrom flask import Flask
app = Flask(__name__)
app.config.from_object('config')
# Now we can access the configuration variables via app.config["VAR_NAME"].

config.py
requirements.txt
run.py
instance/
 config.py
yourapp/
 __init__.py
 models.py
 views.py
 templates/
 static/

# app.py or app/__init__.py
app = Flask(__name__, instance_relative_config=True)
app.config.from_object('config')
app.config.from_pyfile('config.py')

# instance/config.py
SECRET_KEY = 'Sm9obiBTY2hyb20ga2lja3MgYXNz'
STRIPE_API_KEY = 'SmFjb2IgS2FwbGFuLU1vc3MgaXMgYSBoZXJv'
SQLALCHEMY_DATABASE_URI= \\"postgresql://user:TWljaGHFgiBCYXJ0b3N6a2lld2ljeiEh@localhost/databasename"

# config.py
DEBUG = False
SQLALCHEMY_ECHO = False
# instance/config.py
DEBUG = True
SQLALCHEMY_ECHO = True

requirements.txt
run.py
config/
 __init__.py # Empty, just here to tell Python that it's a package.
 default.py
 production.py
 development.py
 staging.py
instance/
 config.py
yourapp/
 __init__.py
 models.py
 views.py
 static/
 templates/

# yourapp/\\_\\_init\\_\\_.py
app = Flask(__name__, instance_relative_config=True)
# Load the default configuration
app.config.from_object('config.default')
# Load the configuration from the instance folder
app.config.from_pyfile('config.py')
# Load the file specified by the APP\\_CONFIG\\_FILE environment variable# Variables defined here will override those in the default configuration
app.config.from_envvar('APP_CONFIG_FILE')

# start.sh
APP\\_CONFIG\\_FILE=/var/www/yourapp/config/production.py
python run.py