[AP-2998] Handle Decimal objects in format_messages (#167)

* added handler for Decimal

* added handler for Decimal

* fix raising typeerror

* Update CHANGELOG.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* unit tests were missed to push

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: amofakhar

CHANGELOG.md

@@ -1,4 +1,12 @@
 # Changelog
+## 3.0.2 (2026-04-22)
+  * Handle Decimal objects in messages
+
+## 3.0.1 (2026-04-21)
+  * Fixed PyPI publisher
+  
+## 3.0.0 (2026-04-20)
+  * Support for Python 3.12
 
 ## 2.0.1 (2021-11-23)
   * Fixed an issue when `format_message` returned newline character

setup.py

@@ -6,7 +6,7 @@
     long_description = fh.read()
 
 setup(name="pipelinewise-singer-python",
-      version='3.0.1',
+      version='3.0.2',
       description="Singer.io utility library - PipelineWise compatible",
       python_requires=">=3.12, <3.13",
       long_description=long_description,

singer/__init__.py

@@ -35,7 +35,8 @@
     write_schema,
     write_state,
     write_version,
-    write_batch
+    write_batch,
+    handler_for_decimal_object
 )
 
 from singer.transform import (

singer/messages.py

@@ -3,6 +3,7 @@
 import pytz
 import orjson
 import ciso8601
+import decimal
 
 import singer.utils as u
 from .logger import get_logger
@@ -291,9 +292,13 @@ def parse_message(msg):
 
     return None
 
+def handler_for_decimal_object(obj):
+    if isinstance(obj, decimal.Decimal):
+        return float(obj)
+    raise TypeError
 
 def format_message(message, option=0):
-    return orjson.dumps(message.asdict(), option=option)
+    return orjson.dumps(message.asdict(), option=option, default=handler_for_decimal_object)
 
 
 def write_message(message):

tests/test_singer.py

@@ -2,6 +2,9 @@
 import orjson
 import unittest
 import dateutil
+import decimal
+
+from unittest.mock import MagicMock
 
 
 class TestSinger(unittest.TestCase):
@@ -206,6 +209,45 @@ def test_format_message(self):
         self.assertEqual(b'{"type":"RECORD","stream":"users","record":{"name":"foo"}}\n',
                          singer.format_message(record_message, option=orjson.OPT_APPEND_NEWLINE))
 
+    def test_default_handler_decimal(self):
+        """Test that decimal.Decimal is converted to a string."""
+        d = decimal.Decimal("10.50")
+        result = singer.handler_for_decimal_object(d)
+        self.assertEqual(result, 10.50)
+        self.assertIsInstance(result, float)
+
+    def test_default_handler_error(self):
+        """Test that unsupported types still raise a TypeError."""
+        with self.assertRaises(TypeError):
+            singer.handler_for_decimal_object(range(5))
+
+    def test_format_message_with_decimals(self):
+        """Test that format_message correctly serializes a message containing decimals."""
+        # Mocking the message object
+        mock_message = MagicMock()
+        mock_message.asdict.return_value = {
+            "id": 1,
+            "price": decimal.Decimal("99.99"),
+            "status": "active"
+        }
+
+        # We expect the Decimal to become a string in the resulting bytes
+        expected_output = b'{"id":1,"price":99.99,"status":"active"}'
+
+        result = singer.format_message(mock_message)
+        self.assertEqual(result, expected_output)
+
+    def test_format_message_options(self):
+        """Test that orjson options (like appending a newline) work."""
+        mock_message = MagicMock()
+        mock_message.asdict.return_value = {"key": "val"}
+
+        # orjson.OPT_APPEND_NEWLINE is an integer bitmask
+        result = singer.format_message(mock_message, option=orjson.OPT_APPEND_NEWLINE)
+
+        # Should end with a newline byte (10)
+        self.assertTrue(result.endswith(b'\n'))
+
 
 if __name__ == '__main__':
     unittest.main()