Make custom JSON encoder support Decimal (apache#16383)

airflow/utils/json.py

@@ -17,6 +17,7 @@
 # under the License.
 
 from datetime import date, datetime
+from decimal import Decimal
 
 import numpy as np
 from flask.json import JSONEncoder
@@ -37,12 +38,19 @@ def __init__(self, *args, **kwargs):
         self.default = self._default
 
     @staticmethod
-    def _default(obj):
+    def _default(obj):  # pylint: disable=too-many-return-statements
         """Convert dates and numpy objects in a json serializable format."""
         if isinstance(obj, datetime):
             return obj.strftime('%Y-%m-%dT%H:%M:%SZ')
         elif isinstance(obj, date):
             return obj.strftime('%Y-%m-%d')
+        elif isinstance(obj, Decimal):
+            _, _, exponent = obj.as_tuple()
+            if exponent >= 0:  # No digits after the decimal point.
+                return int(obj)
+            # Technically lossy due to floating point errors, but the best we
+            # can do without implementing a custom encode function.
+            return float(obj)
         elif isinstance(
             obj,
             (

tests/utils/test_json.py

@@ -16,11 +16,13 @@
 # specific language governing permissions and limitations
 # under the License.
 
+import decimal
 import json
 import unittest
 from datetime import date, datetime
 
 import numpy as np
+import parameterized
 import pytest
 
 from airflow.utils import json as utils_json
@@ -34,6 +36,12 @@ def test_encode_datetime(self):
     def test_encode_date(self):
         assert json.dumps(date(2017, 5, 21), cls=utils_json.AirflowJsonEncoder) == '"2017-05-21"'
 
+    @parameterized.parameterized.expand(
+        [("1", "1"), ("52e4", "520000"), ("2e0", "2"), ("12e-2", "0.12"), ("12.34", "12.34")],
+    )
+    def test_encode_decimal(self, expr, expected):
+        assert json.dumps(decimal.Decimal(expr), cls=utils_json.AirflowJsonEncoder) == expected
+
     def test_encode_numpy_int(self):
         assert json.dumps(np.int32(5), cls=utils_json.AirflowJsonEncoder) == '5'