[simplejson,ultrajson] Implement formatters for simplejson and ultrajson (ujson)

Author: nhairs

docs/changelog.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 - Add support for Python 3.14, PyPy 3.11
+- Add support for [simplejson](https://github.com/simplejson/simplejson)
+- Add support for [ultrajson](https://github.com/ultrajson/ultrajson/tree/main?tab=readme-ov-file#project-status) (`ujson`)
 
 ## [4.0.0](https://github.com/nhairs/python-json-logger/compare/v3.3.3...v4.0.0) - 2025-10-06
 

pylintrc

@@ -3,7 +3,7 @@
 # A comma-separated list of package or module names from where C extensions may
 # be loaded. Extensions are loading into the active Python interpreter and may
 # run arbitrary code.
-extension-pkg-whitelist=orjson
+extension-pkg-whitelist=orjson,ujson
 
 # Add files or directories to the blacklist. They should be base names, not
 # paths.

pyproject.toml

@@ -47,8 +47,11 @@ GitHub = "https://github.com/nhairs/python-json-logger"
 [project.optional-dependencies]
 dev = [
     ## Optional but required for dev
-    "orjson;implementation_name!='pypy'",
     "msgspec;implementation_name!='pypy'",
+    "orjson;implementation_name!='pypy'",
+    "simplejson",
+    "types-simplejson",
+    "ujson",
     ## Lint
     "validate-pyproject[all]",
     "black",

src/pythonjsonlogger/__init__.py

@@ -13,5 +13,7 @@
 
 ### CONSTANTS
 ### ============================================================================
-ORJSON_AVAILABLE = utils.package_is_available("orjson")
 MSGSPEC_AVAILABLE = utils.package_is_available("msgspec")
+ORJSON_AVAILABLE = utils.package_is_available("orjson")
+SIMPLEJSON_AVAILABLE = utils.package_is_available("simplejson")
+ULTRAJSON_AVAILABLE = utils.package_is_available("ujson")

src/pythonjsonlogger/simplejson.py

@@ -0,0 +1,86 @@
+"""JSON Formatter using [simplejson](https://github.com/simplejson/simplejson/tree/master)"""
+
+### IMPORTS
+### ============================================================================
+## Future
+from __future__ import annotations
+
+## Standard Library
+from typing import Any, Optional, Union, Callable
+
+## Installed
+
+## Application
+from . import core
+from . import defaults as d
+from .utils import package_is_available
+
+# We import simplejson after checking it is available
+package_is_available("simplejson", throw_error=True)
+import simplejson  # pylint: disable=wrong-import-position,wrong-import-order
+
+
+### FUNCTIONS
+### ============================================================================
+def simplejson_default(obj: Any) -> Any:
+    """simplejson default encoder function for non-standard types"""
+    if d.use_exception_default(obj):
+        return d.exception_default(obj)
+
+    if d.use_traceback_default(obj):
+        return d.traceback_default(obj)
+
+    if d.use_enum_default(obj):
+        return d.enum_default(obj)
+
+    if d.use_dataclass_default(obj):
+        return d.dataclass_default(obj)
+
+    if d.use_type_default(obj):
+        return d.type_default(obj)
+
+    return d.unknown_default(obj)
+
+
+### CLASSES
+### ============================================================================
+class SimpleJsonFormatter(core.BaseJsonFormatter):
+    """JSON formatter using [simplejson](https://github.com/simplejson/simplejson/tree/master) for encoding.
+
+    !!! warning "Note that simplejson handles certain input different to other encoders in python-json-logger."
+
+        `datetime.datetime` objects use `' '` as the delimiter instead of `'T'`.
+
+        `bytes` can only be encoded if they are valid `utf-8`.
+
+
+    """
+
+    def __init__(
+        self,
+        *args,
+        json_default: Optional[Callable] = simplejson_default,
+        json_indent: Optional[Union[int, str]] = None,
+        **kwargs,
+    ) -> None:
+        """
+        Args:
+            args: see [BaseJsonFormatter][pythonjsonlogger.core.BaseJsonFormatter]
+            json_default: a function for encoding non-standard objects
+            json_indent: indent output with this number of spaces or with the given string.
+            kwargs: see [BaseJsonFormatter][pythonjsonlogger.core.BaseJsonFormatter]
+        """
+        super().__init__(*args, **kwargs)
+
+        # TODO: consider supporting for_json
+        # REF: https://github.com/simplejson/simplejson/blob/master/simplejson/encoder.py#L220
+
+        self.json_encoder = simplejson.JSONEncoder(
+            default=json_default,
+            indent=json_indent,
+        )
+        return
+
+    def jsonify_log_record(self, log_data: core.LogData) -> str:
+        """Returns a json string of the log data."""
+        return self.json_encoder.encode(log_data)

src/pythonjsonlogger/ultrajson.py

@@ -0,0 +1,89 @@
+"""JSON Formatter using [ultrajson](https://github.com/ultrajson/ultrajson)"""
+
+### IMPORTS
+### ============================================================================
+## Future
+from __future__ import annotations
+
+## Standard Library
+from typing import Any, Optional, Callable
+
+## Installed
+
+## Application
+from . import core
+from . import defaults as d
+from .utils import package_is_available
+
+# We import ujson after checking it is available
+package_is_available("ujson", throw_error=True)
+import ujson  # pylint: disable=wrong-import-position,wrong-import-order
+
+
+### FUNCTIONS
+### ============================================================================
+def ujson_default(obj: Any) -> Any:
+    """ujson default encoder function for non-standard types"""
+
+    if d.use_exception_default(obj):
+        return d.exception_default(obj)
+
+    if d.use_traceback_default(obj):
+        return d.traceback_default(obj)
+
+    if d.use_enum_default(obj):
+        return d.enum_default(obj)
+
+    if d.use_dataclass_default(obj):
+        return d.dataclass_default(obj)
+
+    if d.use_type_default(obj):
+        return d.type_default(obj)
+
+    return d.unknown_default(obj)
+
+
+### CLASSES
+### ============================================================================
+class UltraJsonFormatter(core.BaseJsonFormatter):
+    """JSON formatter using [ultrajson](https://github.com/ultrajson/ultrajson) (`ujson`) for encoding.
+
+    !!! warning "UltraJSON is in maintenance mode"
+        [Per README](https://github.com/ultrajson/ultrajson/tree/main?tab=readme-ov-file#project-status) users
+        are encouraged to move to another JSON encoder such as `orjson`.
+
+    !!! warning "Note that ultrajson handles certain input different to other encoders in python-json-logger."
+
+        `datetime.datetime` objects use `' '` as the delimiter instead of `'T'`.
+
+        `bytes` can only be encoded if they are valid `utf-8`.
+
+
+    """
+
+    def __init__(
+        self,
+        *args,
+        json_default: Optional[Callable] = ujson_default,
+        json_indent: int = 0,
+        **kwargs,
+    ) -> None:
+        """
+        Args:
+            args: see [BaseJsonFormatter][pythonjsonlogger.core.BaseJsonFormatter]
+            json_default: a function for encoding non-standard objects
+            json_indent: indent output with this number of spaces.
+            kwargs: see [BaseJsonFormatter][pythonjsonlogger.core.BaseJsonFormatter]
+        """
+        super().__init__(*args, **kwargs)
+
+        self.json_default = json_default
+        self.json_indent = json_indent
+
+        return
+
+    def jsonify_log_record(self, log_data: core.LogData) -> str:
+        """Returns a json string of the log data."""
+        return ujson.dumps(
+            log_data, indent=self.json_indent, default=self.json_default, reject_bytes=False
+        )

tests/test_formatters.py

@@ -31,20 +31,34 @@
 from pythonjsonlogger.core import RESERVED_ATTRS, BaseJsonFormatter, merge_record_extra
 from pythonjsonlogger.json import JsonFormatter
 
+if pythonjsonlogger.MSGSPEC_AVAILABLE:
+    from pythonjsonlogger.msgspec import MsgspecFormatter
+
 if pythonjsonlogger.ORJSON_AVAILABLE:
     from pythonjsonlogger.orjson import OrjsonFormatter
 
-if pythonjsonlogger.MSGSPEC_AVAILABLE:
-    from pythonjsonlogger.msgspec import MsgspecFormatter
+if pythonjsonlogger.SIMPLEJSON_AVAILABLE:
+    from pythonjsonlogger.simplejson import SimpleJsonFormatter
+
+if pythonjsonlogger.ULTRAJSON_AVAILABLE:
+    from pythonjsonlogger.ultrajson import UltraJsonFormatter
 
 ### SETUP
 ### ============================================================================
 ALL_FORMATTERS: list[type[BaseJsonFormatter]] = [JsonFormatter]
-if pythonjsonlogger.ORJSON_AVAILABLE:
-    ALL_FORMATTERS.append(OrjsonFormatter)
+
 if pythonjsonlogger.MSGSPEC_AVAILABLE:
     ALL_FORMATTERS.append(MsgspecFormatter)
 
+if pythonjsonlogger.ORJSON_AVAILABLE:
+    ALL_FORMATTERS.append(OrjsonFormatter)
+
+if pythonjsonlogger.SIMPLEJSON_AVAILABLE:
+    ALL_FORMATTERS.append(SimpleJsonFormatter)
+
+if pythonjsonlogger.ULTRAJSON_AVAILABLE:
+    ALL_FORMATTERS.append(UltraJsonFormatter)
+
 _LOGGER_COUNT = 0
 
 
@@ -543,7 +557,15 @@ def json_default(obj: Any) -> Any:
     env.logger.info("Hello")
     log_json = env.load_json()
 
-    assert log_json["timestamp"] == "2017-07-14T02:40:00+00:00"
+    expected = "2017-07-14T02:40:00+00:00"
+
+    if (pythonjsonlogger.SIMPLEJSON_AVAILABLE and class_ is SimpleJsonFormatter) or (
+        pythonjsonlogger.ULTRAJSON_AVAILABLE and class_ is UltraJsonFormatter
+    ):
+        # simplejson and ujson do not use sep=T
+        expected = expected.replace("T", " ")
+
+    assert log_json["timestamp"] == expected
     return
 
 
@@ -616,6 +638,29 @@ def test_common_types_encoded(
         ):
             pytest.xfail()
 
+    if (pythonjsonlogger.SIMPLEJSON_AVAILABLE and class_ is SimpleJsonFormatter) or (
+        pythonjsonlogger.ULTRAJSON_AVAILABLE and class_ is UltraJsonFormatter
+    ):
+        if obj == b"fancy-bytes-\xf0\xf1":
+            # simplejson attempts to encode using `utf-8` and thus does not support arbitrary bytes
+            # ultrajson prevents bytes or errors when receiving non `utf-8` bytes
+            pytest.xfail()
+
+    ## Overrides
+    if (pythonjsonlogger.SIMPLEJSON_AVAILABLE and class_ is SimpleJsonFormatter) or (
+        pythonjsonlogger.ULTRAJSON_AVAILABLE and class_ is UltraJsonFormatter
+    ):
+        if isinstance(obj, datetime.datetime):
+            # simplejson and ujson do not use sep=T
+            expected = expected.replace("T", " ")
+
+        elif obj is MultiEnum.BYTES or obj == b"some-bytes":
+            expected = "some-bytes"
+
+        elif obj is MultiEnum:
+            expected = list(expected)
+            expected[4] = "some-bytes"
+
     ## Test
     env.set_formatter(class_())
     extra = {