jsonify encodes decimal to str

CHANGES.rst

@@ -15,6 +15,8 @@ Unreleased
 -   Fix registering a blueprint twice with differing names. :issue:`4124`
 -   Fix the type of ``static_folder`` to accept ``pathlib.Path``.
     :issue:`4150`
+-   ``jsonify`` handles ``decimal.Decimal`` by encoding to ``str``.
+    :issue:`4157`
 
 
 Version 2.0.1

src/flask/json/__init__.py

@@ -1,3 +1,4 @@
+import decimal
 import io
 import json as _json
 import typing as t
@@ -47,7 +48,7 @@ class JSONEncoder(_json.JSONEncoder):
         """
         if isinstance(o, date):
             return http_date(o)
-        if isinstance(o, uuid.UUID):
+        if isinstance(o, (decimal.Decimal, uuid.UUID)):
             return str(o)
         if dataclasses and dataclasses.is_dataclass(o):
             return dataclasses.asdict(o)
@@ -117,6 +118,9 @@ def dumps(obj: t.Any, app: t.Optional["Flask"] = None, **kwargs: t.Any) -> str:
         or defaults.
     :param kwargs: Extra arguments passed to :func:`json.dumps`.
 
+    .. versionchanged:: 2.0.2
+        :class:`decimal.Decimal` is supported by converting to a string.
+
     .. versionchanged:: 2.0
         ``encoding`` is deprecated and will be removed in Flask 2.1.
 
@@ -324,6 +328,9 @@ def jsonify(*args: t.Any, **kwargs: t.Any) -> "Response":
     debug mode or if :data:`JSONIFY_PRETTYPRINT_REGULAR` is ``True``,
     the output will be formatted to be easier to read.
 
+    .. versionchanged:: 2.0.2
+        :class:`decimal.Decimal` is supported by converting to a string.
+
     .. versionchanged:: 0.11
         Added support for serializing top-level arrays. This introduces
         a security risk in ancient browsers. See :ref:`security-json`.

tests/test_json.py

@@ -1,4 +1,5 @@
 import datetime
+import decimal
 import io
 import uuid
 
@@ -187,6 +188,11 @@ def test_jsonify_uuid_types(app, client):
     assert rv_uuid == test_uuid
 
 
+def test_json_decimal():
+    rv = flask.json.dumps(decimal.Decimal("0.003"))
+    assert rv == '"0.003"'
+
+
 def test_json_attr(app, client):
     @app.route("/add", methods=["POST"])
     def add():