Extensions¶

Extensions provide additional functionality to applications. Configuration management is shared between applications and extensions in a central location.

Using Extensions¶

from henson import Application
from henson_sqlite import SQLite

app = Application(__name__)
db = SQLite(app)

db.connection.execute('SELECT 1;')

Developing Extensions¶

Henson provides an Extension base class to make extension development easier.

from henson import Extension

class SQLite(Extension):
    DEFAULT_SETTINGS = {'SQLITE_CONNECTION_STRING': ':memory:'}

    def __init__(self, app=None):
        self._connection = None
        super().__init__(app)

    @property
    def connection(self):
        if not self._connection:
            conn_string = self.app.settings['SQLITE_CONNECTION_STRING']
            self._connection = sqlite3.connect(conn_string)
        return self._connection

The Extension class provides two special attributes that are meant to be overridden:

DEFAULT_SETTINGS provides default values for an extension’s settings during the init_app() step. When a value is used by an extension and has a sensible default, it should be stored here (e.g., a database hostname).
REQUIRED_SETTINGS provides a list of keys that are checked for existence during the init_app() step. If one or more required settings are not set on the application instance assigned to the extension, a KeyError is raised. Extensions should set this when a value is required but has no default (e.g., a database password).

Available Extensions¶

Several extensions are available for use: