[PYTHON] Configuration file best practices in Flask

Overview

When creating a configuration file in a Flask application I was studying how to divide each environment and hide the contents.

Read Official Documents and Articles from Overseas I will summarize that. Most of this page is made from the above two Japanese translations.

Config in Flask

Here is a summary of the parts that should be kept in the Flask configuration file.

Basic settings

You can write to the config variable of the Flask instance in dictionary format.

Basic settings

app.config['DEBUG'] = True

Settings from file

You can read the list of settings from the specified file.

Settings from file

#Pattern that directly specifies the file path
app.config.from_pyfile('config_file.cfg')

#A pattern that specifies an environment variable (absolute path) that indicates the location of a file
app.config.from_envvar('FLASK_CONFIG_FILE')

In the file, you can describe the settings in the following INI file format.

config_file.cfg

TESTING=False
DEBUG=True

Settings from object

You can load the settings as a Python object.

Settings from object

app.config.from_object('config.BaseConfig')

I felt that I could see from_json in the source code, but I will ignore it. Within the file you can structure the settings as a Python script as follows:

config.py

class BaseConfig(object):
    DEBUG = False
    TESTING = False


class DevelopmentConfig(BaseConfig):
    DEBUG = True
    TESTING = True


class TestingConfig(BaseConfig):
    DEBUG = False
    TESTING = True

Instance folder

Source version control is essential when developing applications, The configuration file contains passwords, API access keys, etc. There is information that you do not want to include in version control.

In Flask, "instance folder" is This is a function to exclude a specific configuration file from version control.

You can specify an instance folder with an absolute path when initializing Flask.

Specify the path of the instance folder

app = Flask(__name__, instance_path='/path/to/instance/folder')

If this is not specified, the default ʻinstance` directory will be It will be recognized as an instance folder.

If you write as follows, use a relative path from the instance folder You can read the configuration file.

Relative file invocation

app = Flask(__name__, instance_relative_config=True)
app.config.from_pyfile('application.cfg', silent=True)

Here we are referencing ʻinstance / application.cfg. silent = True` suppresses the error when the file is not found.

That doesn't mean it can be excluded from version control, though. Don't forget to put the path of the instance folder in ** .gitignore **. ** **

best practice

There is a section on Best Practices on the official page. The content is short and not very specific. (Due to the problem of English ability, I can only read "It is better to be easy to test" ...)

On the other hand, in the article here, it is stated as follows.

Good practice is to have a default configuration, which is under source control and to override it with sensitive and specific information kept in instance folders. For the default configuration you could use object-based configuration hierarchy(described in Object-based configuration section) and to manage which configuration object to load via environment variables:

• Put the default config file under version control
• Write the default settings as objects and load them using environment variables
• Overwrite sensitive settings with the settings in the instance folder

The last item is to switch between development and production. Writing it as an object should make it easier to test.

As a specific example, it is described as follows.

Best practice (unofficial)

#The basic setting is config under version control.Described as an object in py
config = {
    "development": "bookshelf.config.DevelopmentConfig",
    "testing": "bookshelf.config.TestingConfig",
    "default": "bookshelf.config.DevelopmentConfig"
}

def configure_app(app):
    #Determine the configuration file to read using environment variables
    config_name = os.getenv('FLASK_CONFIGURATION', 'default')
    
    #Read settings as objects
    app.config.from_object(config[config_name])
    
    #Overwrite sensitive settings with the settings in the instance folder
    app.config.from_pyfile('config.cfg', silent=True)

Summary

I think it would be difficult to apply the above settings to all

• If you want to do Hello World !, specify it in ʻapp.config` in solid.
• Set in the config file for smaller applications that you create yourself
• Follow best practices at the level of preparing multiple environments

I had the recognition that.

I've written it for a long time, but in the end it's about whether I can agree with it. Even if the configuration is dirty, there is no problem for the time being as long as the secret file is not leaked.

I hope to find a better shape as the application grows.