Defaults added

docs/changelog.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [3.2.0](https://github.com/nhairs/python-json-logger/compare/v3.1.0...v3.2.0) - 2024-09-10
+
+### Changed
+- `defaults` parameter is no longer ignored and now conforms to the standard library. Setting a defaults dictionary will add the specified keys if the those keys do not exist in a record or weren't passed by the `extra` parameter when logging a message.
+
 ## [3.1.0](https://github.com/nhairs/python-json-logger/compare/v3.0.1...v3.1.0) - 2023-05-28
 
 This splits common funcitonality out to allow supporting other JSON encoders. Although this is a large refactor, backwards compatibility has been maintained.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "python-json-logger"
-version = "3.1.0"
+version = "3.2.0"
 description = "JSON Log Formatter for the Python Logging Package"
 authors = [
     {name = "Zakaria Zajac", email = "zak@madzak.com"},

src/pythonjsonlogger/core.py

@@ -102,6 +102,7 @@ def merge_record_extra(
     target: Dict,
     reserved: Container[str],
     rename_fields: Optional[Dict[str, str]] = None,
+    defaults: Optional[Dict[str, Any]] = None,
 ) -> Dict:
     """
     Merges extra attributes from LogRecord object into target dictionary
@@ -117,7 +118,8 @@ def merge_record_extra(
     """
     if rename_fields is None:
         rename_fields = {}
-    for key, value in record.__dict__.items():
+    record_dict = record.__dict__ if not defaults else (defaults | record.__dict__)
+    for key, value in record_dict.items():
         # this allows to have numeric keys
         if key not in reserved and not (hasattr(key, "startswith") and key.startswith("_")):
             target[rename_fields.get(key, key)] = value
@@ -161,7 +163,9 @@ def __init__(
             style: how to extract log fields from `fmt`
             validate: validate `fmt` against style, if implementing a custom `style` you
                 must set this to `False`.
-            defaults: ignored - kept for compatibility with python 3.10+
+            defaults: a dictionary containing default values for unspecified
+                extras. {"key": 1234} will add the key to the json if
+                unspecified in the extras while logging a message.
             prefix: an optional string prefix added at the beginning of
                 the formatted string
             rename_fields: an optional dict, used to rename field names in the output.
@@ -215,6 +219,7 @@ def __init__(
         self._required_fields = self.parse()
         self._skip_fields = set(self._required_fields)
         self._skip_fields.update(self.reserved_attrs)
+        self.defaults = defaults
         return
 
     def format(self, record: logging.LogRecord) -> str:
@@ -322,6 +327,7 @@ def add_fields(
             log_record,
             reserved=self._skip_fields,
             rename_fields=self.rename_fields,
+            defaults=self.defaults,
         )
 
         if self.timestamp:

tests/test_formatters.py

@@ -174,6 +174,18 @@ def test_percentage_format(env: LoggingEnvironment, class_: type[BaseJsonFormatt
     return
 
 
+@pytest.mark.parametrize("class_", ALL_FORMATTERS)
+def test_defaults_field(env: LoggingEnvironment, class_: type[BaseJsonFormatter]):
+    env.set_formatter(class_(defaults={"first": 1, "second": 2}))
+
+    env.logger.info("testing defaults field", extra={"first": 1234})
+    log_json = env.load_json()
+
+    assert log_json["first"] == 1234
+    assert log_json["second"] == 2
+    return
+
+
 @pytest.mark.parametrize("class_", ALL_FORMATTERS)
 def test_rename_base_field(env: LoggingEnvironment, class_: type[BaseJsonFormatter]):
     env.set_formatter(class_(rename_fields={"message": "@message"}))
@@ -186,6 +198,19 @@ def test_rename_base_field(env: LoggingEnvironment, class_: type[BaseJsonFormatt
     return
 
 
+@pytest.mark.parametrize("class_", ALL_FORMATTERS)
+def test_rename_with_defaults(env: LoggingEnvironment, class_: type[BaseJsonFormatter]):
+    """Make sure that the default fields are also renamed."""
+    env.set_formatter(class_(rename_fields={"custom": "@custom"}, defaults={"custom": 1234}))
+
+    msg = "testing rename with defaults"
+    env.logger.info(msg)
+    log_json = env.load_json()
+
+    assert log_json["@custom"] == 1234
+    return
+
+
 @pytest.mark.parametrize("class_", ALL_FORMATTERS)
 def test_rename_missing(env: LoggingEnvironment, class_: type[BaseJsonFormatter]):
     env.set_formatter(class_(rename_fields={"missing_field": "new_field"}))