CodeVetter · Repo Unpack · Feature catalog
pallets/flask
As a framework, Flask's user-facing features are its decorator registries, its CLI subcommands, and its request/response conveniences. Route registration spans `@route` plus seven method shortcuts including the newly added `@app.query` for HTTP QUERY; class-based views come via `View`/`MethodView`. The `flask` CLI ships `run`, `shell` and `routes` built in, discovers app-provided commands through `app.cli`/`blueprint.cli`, and loads third-party commands from the `flask.commands` entry point group. Response handling covers strings, bytes, dicts, lists, generators, tuples, WSGI callables and Response objects; JSON is routed through a swappable `JSONProvider`. Sessions, flashing, file sending, streaming, signals and blueprint nesting round out the surface.
- Seven HTTP-method route shortcuts are generated through `Scaffold._method_route`: `get`, `query`, `post`, `put`, `delete`, `patch` (plus `route`); `query` is new in 3.2 for the HTTP QUERY method and is also listed in `views.http_method_funcs`.
- `flask run` exposes `--host/-h` (default 127.0.0.1), `--port/-p` (5000), `--cert`/`--key`, `--reload/--no-reload`, `--debugger/--no-debugger`, `--with-threads/--without-threads`, `--extra-files` and `--exclude-patterns`, and inserts `--debug` as its first parameter after definition.
- `flask shell` builds an interactive REPL banner from `current_app.import_name` and `instance_path`, honours `PYTHONSTARTUP`, wires `rlcompleter.Completer` against the shell context rather than `__main__`, then calls `code.interact`.
- `flask routes` supports `--sort` over `endpoint|methods|domain|rule|match` and `--all-methods`, hides HEAD/OPTIONS by default, and renders a padded ASCII table computed from per-column max widths.
- The root CLI group is `FlaskGroup`, which registers three eager options in order (`--env-file`, `--app`, `--debug`) so dotenv loading happens before app import, and sets `auto_envvar_prefix="FLASK"` so every option is also settable via `FLASK_*` env vars.
- App discovery supports four forms: explicit `module:name`, `module:factory(args)` with `ast.literal_eval`-parsed arguments, auto-detection of `app`/`application`/`create_app`/`make_app`, and implicit `wsgi.py` then `app.py` in the CWD.
- `Flask.make_response` accepts str/bytes/bytearray, any iterator (streaming), dict and list (auto-JSON via `self.json.response`), `BaseResponse` subclasses, arbitrary WSGI callables, and 2- or 3-tuples of `(body, status)`, `(body, headers)` or `(body, status, headers)`.
- Class-based views: `View.as_view` supports `init_every_request=False` for a shared instance, applies `cls.decorators` in order, and copies `methods`/`provide_automatic_options` onto the generated function; `MethodView.__init_subclass__` auto-derives `methods` from defined handler names and falls back from HEAD to GET.
- Message flashing writes `session["_flashes"]` via a read-append-reassign pattern (deliberately not `setdefault`, so external session backends stay in sync) and emits the `message_flashed` signal; `get_flashed_messages` caches into `app_ctx._flashes` so repeat calls in one request are stable.
- Ten Blinker signals are defined in one namespace: template-rendered, before-render-template, request-started, request-finished, request-tearing-down, got-request-exception, appcontext-tearing-down, appcontext-pushed, appcontext-popped and message-flashed.
- Async views are opt-in: `ensure_sync` returns plain functions unchanged and wraps coroutine functions via `async_to_sync`, which imports `asgiref.sync.async_to_sync` and raises "Install Flask with the 'async' extra" if asgiref is missing.
- Config can be populated six ways: `from_envvar`, `from_prefixed_env` (JSON-decoded `FLASK_*` vars with `__` nesting), `from_pyfile` (exec'd as a module), `from_object` (uppercase attrs only), `from_file` (pluggable loader, text or binary) and `from_mapping`; `get_namespace` extracts prefixed subsets.
- Three runnable example apps ship in-repo: `examples/tutorial` (flaskr — sqlite blog with auth blueprint, `init-db` CLI command, 4 test modules), `examples/javascript` (fetch/jQuery/XHR templates) and `examples/celery` (`celery_init_app` subclasses `Task` to push an app context around every job).
- `jsonify` and the module-level `flask.json.dumps/dump/loads/load` all delegate to `current_app.json` when an app context is active, falling back to stdlib `json` otherwise, so provider swaps apply globally.