feat(logger): pretty-print JSON when POWERTOOLS_DEV is set

aws_lambda_powertools/logging/formatter.py

@@ -111,9 +111,15 @@ def __init__(
             Key-value to be included in log messages
 
         """
+
         self.json_deserializer = json_deserializer or json.loads
         self.json_default = json_default or str
-        self.json_serializer = json_serializer or partial(json.dumps, default=self.json_default, separators=(",", ":"))
+        self.json_indent = (
+            constants.PRETTY_INDENT if os.getenv("POWERTOOLS_DEV", "").lower() == "true" else constants.COMPACT_INDENT
+        )  # indented json serialization when in AWS SAM Local
+        self.json_serializer = json_serializer or partial(
+            json.dumps, default=self.json_default, separators=(",", ":"), indent=self.json_indent
+        )
 
         self.datefmt = datefmt
         self.use_datetime_directive = use_datetime_directive

aws_lambda_powertools/shared/constants.py

@@ -32,3 +32,6 @@
     "cold_start",
     "xray_trace_id",
 ]
+
+PRETTY_INDENT: int = 4
+COMPACT_INDENT = None

docs/core/logger.md

@@ -369,6 +369,9 @@ If you prefer configuring it separately, or you'd want to bring this JSON Format
 | **`log_record_order`**       | set order of log keys when logging                                                                                       | `["level", "location", "message", "timestamp"]`               |
 | **`kwargs`**                 | key-value to be included in log messages                                                                                 | `None`                                                        |
 
+???+ info
+    When `POWERTOOLS_DEV` env var is present and set to `"true"`, Logger's default serializer (`json.dumps`) will pretty-print log messages for easier readability.
+
 ```python hl_lines="2 7-8" title="Pre-configuring Lambda Powertools Formatter"
 --8<-- "examples/logger/src/powertools_formatter_setup.py"
 ```

tests/functional/test_logger_powertools_formatter.py

@@ -1,13 +1,15 @@
 """aws_lambda_logging tests."""
 import io
 import json
+import os
 import random
 import string
 import time
 
 import pytest
 
 from aws_lambda_powertools import Logger
+from aws_lambda_powertools.shared import constants
 
 
 @pytest.fixture
@@ -288,3 +290,22 @@ def test_log_formatting(stdout, service_name):
 
     # THEN the formatting should be applied (NB. this is valid json, but hasn't be parsed)
     assert log_dict["message"] == '["foo bar 123 [1, None]", null]'
+
+
+def test_log_json_indent_compact_indent(stdout, service_name, monkeypatch):
+    # GIVEN a logger with default settings and WHEN POWERTOOLS_DEV is not set
+    if "POWERTOOLS_DEV" in os.environ:
+        monkeypatch.delenv(name="POWERTOOLS_DEV")
+    logger = Logger(service=service_name, stream=stdout)
+    logger.info("Test message")
+    # THEN the json should not be indented using constant.PRETTY_INDENT blank spaces
+    assert " " * constants.PRETTY_INDENT not in stdout.getvalue()
+
+
+def test_log_json_pretty_indent(stdout, service_name, monkeypatch):
+    # GIVEN a logger with default settings and WHEN POWERTOOLS_DEV=="true"
+    monkeypatch.setenv(name="POWERTOOLS_DEV", value="true")
+    logger = Logger(service=service_name, stream=stdout)
+    logger.info("Test message")
+    # THEN the json should contain indentation (of constant.PRETTY_INDENT blank spaces)
+    assert " " * constants.PRETTY_INDENT in stdout.getvalue()