add celery example

examples/celery/src/task_app/__init__.py

@@ -0,0 +1,39 @@
+from celery import Celery
+from celery import Task
+from flask import Flask
+from flask import render_template
+
+
+def create_app() -> Flask:
+    app = Flask(__name__)
+    app.config.from_mapping(
+        CELERY=dict(
+            broker_url="redis://localhost",
+            result_backend="redis://localhost",
+            task_ignore_result=True,
+        ),
+    )
+    app.config.from_prefixed_env()
+    celery_init_app(app)
+
+    @app.route("/")
+    def index() -> str:
+        return render_template("index.html")
+
+    from . import views
+
+    app.register_blueprint(views.bp)
+    return app
+
+
+def celery_init_app(app: Flask) -> Celery:
+    class FlaskTask(Task):
+        def __call__(self, *args: object, **kwargs: object) -> object:
+            with app.app_context():
+                return self.run(*args, **kwargs)
+
+    celery_app = Celery(app.name, task_cls=FlaskTask)
+    celery_app.config_from_object(app.config["CELERY"])
+    celery_app.set_default()
+    app.extensions["celery"] = celery_app
+    return celery_app