Extending Flask using the Flask Plugins API 

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About One of the organizer of Python Mauritius Usergroup (pymug) / FlaskCon / PyCon Africa OpenSource https://www.compileralchemy.com or Qr 3 

so, about handles twitter @osdotsystem https://fosstodon.org/@osdotsystem linkedin.com/in/appinv/ 4 

Extending Flask using the Flask Plugins API 5 

Why this talk? 6 

encourage people to maintain Flask projects Pallets Eco 7 

encourage people to write extensions give users SUPER powers improve Flask dev experience contributes to make Flask a compelling choice saves time 8 

understand extensions the seed to muster the courage to dive into codebases 9 

Approaches to plugins in Python 10 

The auto-load method python ---> find packages start with fruit_ | V iterate find attributes 11 

Plugins list method python ---> developers specify plugins | V load iterate find attributes 12 

Plugin manager python ---> plugin manager | V find plugin load extract info pass back 13 

Flask app = create_app() | app ---. | V .---------. | plugin1 | plugin1.init_app(app) .---------. | app <--. // modified | app ---. | V .---------. | plugin2 | plugin2.init_app(app) .---------. | app <--. // modified | 14 

Order of plugins matter sometimes 15 

Not always need to be named .init_app 16 

Really? 17 

Yes, docs says The most common pattern is to create a class that represents the extension’s configuration and behavior, with an init_app method to apply the extension instance to the given application instance. 18 

Also The only time the extension should have direct access to an app is during init_app, otherwise it should use current_app. 19 

class HelloExtension: def __init__(self, app=None): if app is not None: self.init_app(app) def init_app(self, app): app.before_request(...) 20 

before_request(f) Register a function to run before each request. @app.before_request def load_user(): if "user_id" in session: g.user = db.session.get(session["user_id"]) # ... def init_app(self, app): app.before_request(greet_user) def greet_user(self): print('Welcome to FlaskCon') 21 

So, building extensions is about 22 

knowing Flask internals well ... 23 

Useful tips 24 

current_app g global variables, during request, per thread 25 

Real app current_app._get_current_object() 26 

blueprint also has cli.group 27 

Common ideas 28 

Configs -> Flask app config 29 

flask-tabler-icons 30 

from typing import Any from flask import Blueprint, Flask # version is same as tabler-icons __version__ = "3.3.0" class TablerIcons: def __init__(self, app: Any = None) -> None: if app is not None: self.init_app(app) def init_app(self, app: Flask) -> None: if not hasattr(app, "extensions"): app.extensions = {} app.extensions["tabler_icons"] = self bp = Blueprint( "tabler_icons", __name__, static_folder="static", static_url_path=f"/tabler-icons{app.static_url_path}", template_folder="templates", ) app.register_blueprint(bp) app.jinja_env.globals["tabler_icons"] = self app.config.setdefault("TABLER_ICON_SIZE", 24) 31 

{% macro fill_css(value="", prefix="", yes_value="", postfix="") %} ... {% endmacro %} {% macro render_icon(icon, color="", bold=false, class="", style="", animation="", css_color="", size=0) %} {% if css_color %} {% set css_color = "color: %s;"|format(css_color) %} {% endif %} {% set bold = " font-weight: bold;" if bold else "" %} {% set animation_css = fill_css(animation, ' icon-') %} {% if color or class %} {% set class = "%s %s"|format(class, ("text-" + color) if color else "") %} {% endif %} {% endmacro %} 32 

static/tabler-icon.svg 33 

flask-MonitoringDashboard 34 

from flask import Flask import flask_monitoringdashboard as dashboard app = Flask(__name__) @app.route("/test") def test(): return 'ok' dashboard.bind(app) // here app.run() 35 

Flask-sqlalchemy 36 

def init_app(self, app: Flask) -> None: if "sqlalchemy" in app.extensions: raise RuntimeError( "A 'SQLAlchemy' instance has already been registered on this Flask app." " Import and use that instance instead." ) app.extensions["sqlalchemy"] = self app.teardown_appcontext(self._teardown_session) if self._add_models_to_shell: from .cli import add_models_to_shell app.shell_context_processor(add_models_to_shell) basic_uri: str | sa.engine.URL | None = app.config.setdefault( "SQLALCHEMY_DATABASE_URI", None ) basic_engine_options = self._engine_options.copy() basic_engine_options.update( app.config.setdefault("SQLALCHEMY_ENGINE_OPTIONS", {}) ) echo: bool = app.config.setdefault("SQLALCHEMY_ECHO", False) config_binds: dict[str | None, str | sa.engine.URL | dict[str, t.Any]] = ( app.config.setdefault("SQLALCHEMY_BINDS", {}) ) engine_options: dict[str | None, dict[str, t.Any]] = {} 37 

# Build the engine config for each bind key. for key, value in config_binds.items(): engine_options[key] = self._engine_options.copy() if isinstance(value, (str, sa.engine.URL)): engine_options[key]["url"] = value else: engine_options[key].update(value) # Build the engine config for the default bind key. if basic_uri is not None: basic_engine_options["url"] = basic_uri if "url" in basic_engine_options: engine_options.setdefault(None, {}).update(basic_engine_options) if not engine_options: raise RuntimeError( "Either 'SQLALCHEMY_DATABASE_URI' or 'SQLALCHEMY_BINDS' must be set." ) 38 

engines = self._app_engines.setdefault(app, {}) # Dispose existing engines in case init_app is called again. if engines: for engine in engines.values(): engine.dispose() engines.clear() # Create the metadata and engine for each bind key. for key, options in engine_options.items(): self._make_metadata(key) options.setdefault("echo", echo) options.setdefault("echo_pool", echo) self._apply_driver_defaults(options, app) engines[key] = self._make_engine(key, options, app) if app.config.setdefault("SQLALCHEMY_RECORD_QUERIES", False): from . import record_queries for engine in engines.values(): record_queries._listen(engine) if app.config.setdefault("SQLALCHEMY_TRACK_MODIFICATIONS", False): from . import track_modifications track_modifications._listen(self.session) 39 

Plugins reaching EOL 40 

See pallets-eco 41 

That's all folks 42