Merge pull request #4672 from greyli/return-list

Allow to return list as JSON

CHANGES.rst

@@ -65,6 +65,9 @@ Unreleased
         ``with client`` block. It will be cleaned up when
         ``response.get_data()`` or ``response.close()`` is called.
 
+-   Allow returning a list from a view function, to convert it to a
+    JSON response like a dict is. :issue:`4672`
+
 
 Version 2.1.3
 -------------

docs/quickstart.rst

@@ -681,22 +681,25 @@ The return value from a view function is automatically converted into
 a response object for you. If the return value is a string it's
 converted into a response object with the string as response body, a
 ``200 OK`` status code and a :mimetype:`text/html` mimetype. If the
-return value is a dict, :func:`jsonify` is called to produce a response.
-The logic that Flask applies to converting return values into response
-objects is as follows:
+return value is a dict or list, :func:`jsonify` is called to produce a
+response. The logic that Flask applies to converting return values into
+response objects is as follows:
 
 1.  If a response object of the correct type is returned it's directly
     returned from the view.
 2.  If it's a string, a response object is created with that data and
     the default parameters.
-3.  If it's a dict, a response object is created using ``jsonify``.
-4.  If a tuple is returned the items in the tuple can provide extra
+3.  If it's an iterator or generator returning strings or bytes, it is
+    treated as a streaming response.
+4.  If it's a dict or list, a response object is created using
+    :func:`~flask.json.jsonify`.
+5.  If a tuple is returned the items in the tuple can provide extra
     information. Such tuples have to be in the form
     ``(response, status)``, ``(response, headers)``, or
     ``(response, status, headers)``. The ``status`` value will override
     the status code and ``headers`` can be a list or dictionary of
     additional header values.
-5.  If none of that works, Flask will assume the return value is a
+6.  If none of that works, Flask will assume the return value is a
     valid WSGI application and convert that into a response object.
 
 If you want to get hold of the resulting response object inside the view
@@ -727,8 +730,8 @@ APIs with JSON
 ``````````````
 
 A common response format when writing an API is JSON. It's easy to get
-started writing such an API with Flask. If you return a ``dict`` from a
-view, it will be converted to a JSON response.
+started writing such an API with Flask. If you return a ``dict`` or
+``list`` from a view, it will be converted to a JSON response.
 
 .. code-block:: python
 
@@ -741,20 +744,20 @@ view, it will be converted to a JSON response.
             "image": url_for("user_image", filename=user.image),
         }
 
-Depending on your API design, you may want to create JSON responses for
-types other than ``dict``. In that case, use the
-:func:`~flask.json.jsonify` function, which will serialize any supported
-JSON data type. Or look into Flask community extensions that support
-more complex applications.
-
-.. code-block:: python
-
-    from flask import jsonify
-
     @app.route("/users")
     def users_api():
         users = get_all_users()
-        return jsonify([user.to_json() for user in users])
+        return [user.to_json() for user in users]
+
+This is a shortcut to passing the data to the
+:func:`~flask.json.jsonify` function, which will serialize any supported
+JSON data type. That means that all the data in the dict or list must be
+JSON serializable.
+
+For complex types such as database models, you'll want to use a
+serialization library to convert the data to valid JSON types first.
+There are many serialization libraries and Flask API extensions
+maintained by the community that support more complex applications.
 
 
 .. _sessions:

src/flask/app.py

@@ -1830,6 +1830,9 @@ class Flask(Scaffold):
             ``dict``
                 A dictionary that will be jsonify'd before being returned.
 
+            ``list``
+                A list that will be jsonify'd before being returned.
+
             ``generator`` or ``iterator``
                 A generator that returns ``str`` or ``bytes`` to be
                 streamed as the response.
@@ -1855,6 +1858,7 @@ class Flask(Scaffold):
 
         .. versionchanged:: 2.2
             A generator will be converted to a streaming response.
+            A list will be converted to a JSON response.
 
         .. versionchanged:: 1.1
             A dict will be converted to a JSON response.
@@ -1907,7 +1911,7 @@ class Flask(Scaffold):
                     headers=headers,  # type: ignore[arg-type]
                 )
                 status = headers = None
-            elif isinstance(rv, dict):
+            elif isinstance(rv, (dict, list)):
                 rv = jsonify(rv)
             elif isinstance(rv, BaseResponse) or callable(rv):
                 # evaluate a WSGI callable, or coerce a different response
@@ -1920,15 +1924,17 @@ class Flask(Scaffold):
                     raise TypeError(
                         f"{e}\nThe view function did not return a valid"
                         " response. The return type must be a string,"
-                        " dict, tuple, Response instance, or WSGI"
-                        f" callable, but it was a {type(rv).__name__}."
+                        " dict, list, tuple with headers or status,"
+                        " Response instance, or WSGI callable, but it"
+                        f" was a {type(rv).__name__}."
                     ).with_traceback(sys.exc_info()[2]) from None
             else:
                 raise TypeError(
                     "The view function did not return a valid"
                     " response. The return type must be a string,"
-                    " dict, tuple, Response instance, or WSGI"
-                    f" callable, but it was a {type(rv).__name__}."
+                    " dict, list, tuple with headers or status,"
+                    " Response instance, or WSGI callable, but it was a"
+                    f" {type(rv).__name__}."
                 )
 
         rv = t.cast(Response, rv)

src/flask/typing.py

@@ -7,7 +7,13 @@ if t.TYPE_CHECKING:  # pragma: no cover
 
 # The possible types that are directly convertible or are a Response object.
 ResponseValue = t.Union[
-    "Response", str, bytes, t.Dict[str, t.Any], t.Iterator[str], t.Iterator[bytes]
+    "Response",
+    str,
+    bytes,
+    t.List[t.Any],
+    t.Dict[str, t.Any],
+    t.Iterator[str],
+    t.Iterator[bytes],
 ]
 
 # the possible types for an individual HTTP header

tests/test_basic.py

@@ -1166,6 +1166,10 @@ def test_response_types(app, client):
     def from_dict():
         return {"foo": "bar"}, 201
 
+    @app.route("/list")
+    def from_list():
+        return ["foo", "bar"], 201
+
     assert client.get("/text").data == "Hällo Wörld".encode()
     assert client.get("/bytes").data == "Hällo Wörld".encode()
 
@@ -1205,6 +1209,10 @@ def test_response_types(app, client):
     assert rv.json == {"foo": "bar"}
     assert rv.status_code == 201
 
+    rv = client.get("/list")
+    assert rv.json == ["foo", "bar"]
+    assert rv.status_code == 201
+
 
 def test_response_type_errors():
     app = flask.Flask(__name__)

tests/typing/typing_route.py

@@ -25,7 +25,17 @@ def hello_bytes() -> bytes:
 
 @app.route("/json")
 def hello_json() -> Response:
-    return jsonify({"response": "Hello, World!"})
+    return jsonify("Hello, World!")
+
+
+@app.route("/json/dict")
+def hello_json_dict() -> t.Dict[str, t.Any]:
+    return {"response": "Hello, World!"}
+
+
+@app.route("/json/dict")
+def hello_json_list() -> t.List[t.Any]:
+    return [{"message": "Hello"}, {"message": "World"}]
 
 
 @app.route("/generator")