Merge pull request #3195 from eruvanos/json_support_dataclass

Support dataclass in JSONEncoder (if available)

CHANGES.rst

@@ -38,6 +38,8 @@ Unreleased
     dependency to >= 0.15. :issue:`3022`
 -   Support ``static_url_path`` that ends with a forward slash.
     :issue:`3134`
+-   :meth:`jsonify` supports :class:`dataclasses.dataclass` objects.
+    :pr:`3195`
 
 .. _#2935: https://github.com/pallets/flask/issues/2935
 .. _#2957: https://github.com/pallets/flask/issues/2957

flask/json/__init__.py

@@ -20,6 +20,10 @@ from jinja2 import Markup
 # depend anyways.
 from itsdangerous import json as _json
 
+try:
+    import dataclasses
+except ImportError:
+    dataclasses = None
 
 # Figure out if simplejson escapes slashes.  This behavior was changed
 # from one version to another without reason.
@@ -54,11 +58,15 @@ def _wrap_writer_for_text(fp, encoding):
 
 
 class JSONEncoder(_json.JSONEncoder):
-    """The default Flask JSON encoder.  This one extends the default simplejson
-    encoder by also supporting ``datetime`` objects, ``UUID`` as well as
-    ``Markup`` objects which are serialized as RFC 822 datetime strings (same
-    as the HTTP date format).  In order to support more data types override the
-    :meth:`default` method.
+    """The default Flask JSON encoder. This one extends the default
+    encoder by also supporting ``datetime``, ``UUID``, ``dataclasses``,
+    and ``Markup`` objects.
+
+    ``datetime`` objects are serialized as RFC 822 datetime strings.
+    This is the same as the HTTP date format.
+
+    In order to support more data types, override the :meth:`default`
+    method.
     """
 
     def default(self, o):
@@ -84,6 +92,8 @@ class JSONEncoder(_json.JSONEncoder):
             return http_date(o.timetuple())
         if isinstance(o, uuid.UUID):
             return str(o)
+        if dataclasses and dataclasses.is_dataclass(o):
+            return dataclasses.asdict(o)
         if hasattr(o, "__html__"):
             return text_type(o.__html__())
         return _json.JSONEncoder.default(self, o)

tests/test_basic.py

@@ -10,6 +10,7 @@
 """
 
 import re
+import sys
 import time
 import uuid
 from datetime import datetime
@@ -1289,6 +1290,14 @@ def test_jsonify_mimetype(app, req_ctx):
     assert rv.mimetype == "application/vnd.api+json"
 
 
+@pytest.mark.skipif(sys.version_info < (3, 7), reason="requires Python >= 3.7")
+def test_json_dump_dataclass(app, req_ctx):
+    from dataclasses import make_dataclass
+    Data = make_dataclass("Data", [("name", str)])
+    value = flask.json.dumps(Data("Flask"), app=app)
+    value = flask.json.loads(value, app=app)
+    assert value == {"name": "Flask"}
+
 def test_jsonify_args_and_kwargs_check(app, req_ctx):
     with pytest.raises(TypeError) as e:
         flask.jsonify("fake args", kwargs="fake")