before_request() — flask Function Reference

Architecture documentation for the before_request() function in scaffold.py from the flask codebase.

Function python ApplicationCore Scaffolding calls 1

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ApplicationCore→ Scaffolding→ before_request() — flask Function Reference

Dependency Diagram

graph TD
  c81be821_0802_b9e4_55aa_2dfea5badef3["before_request()"]
  a813bd5c_bf41_d926_8dde_6a113d5e0018["Scaffold"]
  c81be821_0802_b9e4_55aa_2dfea5badef3 -->|defined in| a813bd5c_bf41_d926_8dde_6a113d5e0018
  cd459c23_b1c5_45ac_a393_26c2ff268367["get()"]
  c81be821_0802_b9e4_55aa_2dfea5badef3 -->|calls| cd459c23_b1c5_45ac_a393_26c2ff268367
  style c81be821_0802_b9e4_55aa_2dfea5badef3 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

src/flask/sansio/scaffold.py lines 460–484

    def before_request(self, f: T_before_request) -> T_before_request:
        """Register a function to run before each request.

        For example, this can be used to open a database connection, or
        to load the logged in user from the session.

        .. code-block:: python

            @app.before_request
            def load_user():
                if "user_id" in session:
                    g.user = db.session.get(session["user_id"])

        The function will be called without any arguments. If it returns
        a non-``None`` value, the value is handled as if it was the
        return value from the view, and further request handling is
        stopped.

        This is available on both app and blueprint objects. When used on an app, this
        executes before every request. When used on a blueprint, this executes before
        every request that the blueprint handles. To register with a blueprint and
        execute before every request, use :meth:`.Blueprint.before_app_request`.
        """
        self.before_request_funcs.setdefault(None, []).append(f)
        return f