feat: add support for logger inheritance (#99)

* chore: uppercase env var log level value Signed-off-by: heitorlessa <lessa@amazon.co.uk> * feat: add keys to existing formatter Signed-off-by: heitorlessa <lessa@amazon.co.uk> * chore: remove duplicate parameters docstring Signed-off-by: heitorlessa <lessa@amazon.co.uk> * feat: add name parameter Signed-off-by: heitorlessa <lessa@amazon.co.uk> * feat: support logging inheritance * chore: spelling Signed-off-by: heitorlessa <lessa@amazon.co.uk> * improv: make handler prop private Signed-off-by: heitorlessa <lessa@amazon.co.uk> * feat: fetch random logger; remove dead loc * improv: cover child logger independence * improv: addresses nico feedback on missing test Signed-off-by: heitorlessa <lessa@amazon.co.uk> * fix: docstring name parameter short description Signed-off-by: heitorlessa <lessa@amazon.co.uk> * improv: logger inheritance via child param Signed-off-by: heitorlessa <lessa@amazon.co.uk> * improv: update tests Signed-off-by: heitorlessa <lessa@amazon.co.uk> * improv: logger test utility no longer necessary Signed-off-by: heitorlessa <lessa@amazon.co.uk> * improv: make test name more descriptive Signed-off-by: heitorlessa <lessa@amazon.co.uk> * fix: remove logger utility as it's no longer used Signed-off-by: heitorlessa <lessa@amazon.co.uk> * fix: address feedback on consistency Signed-off-by: heitorlessa <lessa@amazon.co.uk> * improv: turn log_level input case insensitive * chore: add unreleased changes to Logger * docs: adds reusing logger across your code section Documents new Logger feature to support logging inheritance using the new `child` parameter.
aws-powertools · Aug 14, 2020 · b808b1a · b808b1a
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -5,6 +5,11 @@ 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).
 
 ## [Unreleased]
+### Added
+- **Logger**: Support for logger inheritance with `child` parameter
+
+### Fixed
+- **Logger**: Log level is now case insensitive via params and env var
 
 ## [1.0.2] - 2020-07-16
 ### Fixed

diff --git a/aws_lambda_powertools/logging/formatter.py b/aws_lambda_powertools/logging/formatter.py
@@ -56,6 +56,9 @@ def __init__(self, **kwargs):
         self.format_dict.update(kwargs)
         self.default_json_formatter = kwargs.pop("json_default", json_formatter)
 
+    def update_formatter(self, **kwargs):
+        self.format_dict.update(kwargs)
+
     def format(self, record):  # noqa: A003
         record_dict = record.__dict__.copy()
         record_dict["asctime"] = self.formatTime(record, self.datefmt)

diff --git a/aws_lambda_powertools/logging/logger.py b/aws_lambda_powertools/logging/logger.py
@@ -1,5 +1,5 @@
-import copy
 import functools
+import inspect
 import logging
 import os
 import random
@@ -34,7 +34,7 @@ def _is_cold_start() -> bool:
     return cold_start
 
 
-class Logger(logging.Logger):
+class Logger:
     """Creates and setups a logger to format statements in JSON.
 
     Includes service name and any additional key=value into logs
@@ -55,6 +55,8 @@ class Logger(logging.Logger):
         service name to be appended in logs, by default "service_undefined"
     level : str, optional
         logging.level, by default "INFO"
+    child: bool, optional
+        create a child Logger named <service>.<caller_file_name>, False by default
     sample_rate: float, optional
         sample rate for debug calls within execution context defaults to 0.0
     stream: sys.stdout, optional
@@ -80,7 +82,7 @@ class Logger(logging.Logger):
         >>> def handler(event, context):
                 logger.info("Hello")
 
-    **Append payment_id to previously setup structured log logger**
+    **Append payment_id to previously setup logger**
 
         >>> from aws_lambda_powertools import Logger
         >>> logger = Logger(service="payment")
@@ -89,18 +91,16 @@ class Logger(logging.Logger):
                 logger.structure_logs(append=True, payment_id=event["payment_id"])
                 logger.info("Hello")
 
-    Parameters
-    ----------
-    logging : logging.Logger
-        Inherits Logger
-    service: str
-        name of the service to create the logger for, "service_undefined" by default
-    level: str, int
-        log level, INFO by default
-    sampling_rate: float
-        debug log sampling rate, 0.0 by default
-    stream: sys.stdout
-        log stream, stdout by default
+    **Create child Logger using logging inheritance via child param**
+
+        >>> # app.py
+        >>> import another_file
+        >>> from aws_lambda_powertools import Logger
+        >>> logger = Logger(service="payment")
+        >>>
+        >>> # another_file.py
+        >>> from aws_lambda_powertools import Logger
+        >>> logger = Logger(service="payment", child=True)
 
     Raises
     ------
@@ -112,19 +112,72 @@ def __init__(
         self,
         service: str = None,
         level: Union[str, int] = None,
+        child: bool = False,
         sampling_rate: float = None,
         stream: sys.stdout = None,
         **kwargs,
     ):
         self.service = service or os.getenv("POWERTOOLS_SERVICE_NAME") or "service_undefined"
         self.sampling_rate = sampling_rate or os.getenv("POWERTOOLS_LOGGER_SAMPLE_RATE") or 0.0
-        self.log_level = level or os.getenv("LOG_LEVEL") or logging.INFO
-        self.handler = logging.StreamHandler(stream) if stream is not None else logging.StreamHandler(sys.stdout)
+        self.log_level = self._get_log_level(level)
+        self.child = child
+        self._handler = logging.StreamHandler(stream) if stream is not None else logging.StreamHandler(sys.stdout)
         self._default_log_keys = {"service": self.service, "sampling_rate": self.sampling_rate}
-        self.log_keys = copy.copy(self._default_log_keys)
-
-        super().__init__(name=self.service, level=self.log_level)
-
+        self._logger = self._get_logger()
+
+        self._init_logger(**kwargs)
+
+    def __getattr__(self, name):
+        # Proxy attributes not found to actual logger to support backward compatibility
+        # https://github.com/awslabs/aws-lambda-powertools-python/issues/97
+        return getattr(self._logger, name)
+
+    def _get_log_level(self, level: str):
+        """ Returns preferred log level set by the customer in upper case """
+        log_level: str = level or os.getenv("LOG_LEVEL")
+        log_level = log_level.upper() if log_level is not None else logging.INFO
+
+        return log_level
+
+    def _get_logger(self):
+        """ Returns a Logger named {self.service}, or {self.service.filename} for child loggers"""
+        logger_name = self.service
+        if self.child:
+            logger_name = f"{self.service}.{self._get_caller_filename()}"
+
+        return logging.getLogger(logger_name)
+
+    def _get_caller_filename(self):
+        """ Return caller filename by finding the caller frame """
+        # Current frame         => _get_logger()
+        # Previous frame        => logger.py
+        # Before previous frame => Caller
+        frame = inspect.currentframe()
+        caller_frame = frame.f_back.f_back.f_back
+        filename = caller_frame.f_globals["__name__"]
+
+        return filename
+
+    def _init_logger(self, **kwargs):
+        """Configures new logger"""
+
+        # Skip configuration if it's a child logger to prevent
+        # multiple handlers being attached as well as different sampling mechanisms
+        # and multiple messages from being logged as handlers can be duplicated
+        if not self.child:
+            self._configure_sampling()
+            self._logger.setLevel(self.log_level)
+            self._logger.addHandler(self._handler)
+            self.structure_logs(**kwargs)
+
+    def _configure_sampling(self):
+        """Dynamically set log level based on sampling rate
+
+        Raises
+        ------
+        InvalidLoggerSamplingRateError
+            When sampling rate provided is not a float
+        """
         try:
             if self.sampling_rate and random.random() <= float(self.sampling_rate):
                 logger.debug("Setting log level to Debug due to sampling rate")
@@ -134,12 +187,8 @@ def __init__(
                 f"Expected a float value ranging 0 to 1, but received {self.sampling_rate} instead. Please review POWERTOOLS_LOGGER_SAMPLE_RATE environment variable."  # noqa E501
             )
 
-        self.setLevel(self.log_level)
-        self.structure_logs(**kwargs)
-        self.addHandler(self.handler)
-
     def inject_lambda_context(self, lambda_handler: Callable[[Dict, Any], Any] = None, log_event: bool = False):
-        """Decorator to capture Lambda contextual info and inject into struct logging
+        """Decorator to capture Lambda contextual info and inject into logger
 
         Parameters
         ----------
@@ -216,21 +265,24 @@ def structure_logs(self, append: bool = False, **kwargs):
         append : bool, optional
             [description], by default False
         """
-        self.handler.setFormatter(JsonFormatter(**self._default_log_keys, **kwargs))
-
-        if append:
-            new_keys = {**self.log_keys, **kwargs}
-            self.handler.setFormatter(JsonFormatter(**new_keys))
 
-        self.log_keys.update(**kwargs)
+        # Child loggers don't have handlers attached, use its parent handlers
+        handlers = self._logger.parent.handlers if self.child else self._logger.handlers
+        for handler in handlers:
+            if append:
+                # Update existing formatter in an existing logger handler
+                handler.formatter.update_formatter(**kwargs)
+            else:
+                # Set a new formatter for a logger handler
+                handler.setFormatter(JsonFormatter(**self._default_log_keys, **kwargs))
 
 
 def set_package_logger(
     level: Union[str, int] = logging.DEBUG, stream: sys.stdout = None, formatter: logging.Formatter = None
 ):
     """Set an additional stream handler, formatter, and log level for aws_lambda_powertools package logger.
 
-    **Package log by default is supressed (NullHandler), this should only used for debugging.
+    **Package log by default is suppressed (NullHandler), this should only used for debugging.
     This is separate from application Logger class utility**
 
     Example

diff --git a/docs/content/core/logger.mdx b/docs/content/core/logger.mdx
@@ -183,6 +183,41 @@ def handler(event, context):
 ```
 </details>
 
+## Reusing Logger across your code
+
+Logger supports inheritance via `child` parameter. This allows you to create multiple Loggers across your code base, and propagate changes such as new keys to all Loggers.
+
+```python:title=collect.py
+# POWERTOOLS_SERVICE_NAME: "payment"
+import shared # Creates a child logger named "payment.shared"
+from aws_lambda_powertools import Logger
+
+logger = Logger()
+
+def handler(event, context):
+  shared.inject_payment_id(event) # highlight-line
+  logger.structure_logs(append=True, order_id=event["order_id"]) # highlight-line
+      ...
+```
+
+```python:title=shared.py
+# POWERTOOLS_SERVICE_NAME: "payment"
+from aws_lambda_powertools import Logger
+
+logger = Logger(child=True) # highlight-line
+
+def inject_payment_id(event):
+    logger.structure_logs(append=True, payment_id=event["payment_id"])
+```
+
+In this example, `Logger` will create a parent logger named `payment` and a child logger named `payment.shared`. Any changes in the parent and child `Loggers` will be propagated among them.
+
+If you ever forget to use `child` param, we will return an existing `Logger` with the same `service` name.
+
+<Note type="info">
+	Child loggers will be named after the following convention <code>service.filename</code>.
+</Note><br/>
+
 ## Sampling debug logs
 
 You can dynamically set a percentage of your logs to **DEBUG** level using `sample_rate` param or via env var `POWERTOOLS_LOGGER_SAMPLE_RATE`.

diff --git a/tests/functional/test_aws_lambda_logging.py b/tests/functional/test_aws_lambda_logging.py
@@ -1,7 +1,6 @@
 """aws_lambda_logging tests."""
 import io
 import json
-import logging
 
 import pytest
 
@@ -13,25 +12,8 @@ def stdout():
     return io.StringIO()
 
 
-@pytest.fixture
-def handler(stdout):
-    return logging.StreamHandler(stdout)
-
-
-@pytest.fixture
-def logger():
-    return logging.getLogger(__name__)
-
-
-@pytest.fixture
-def root_logger(handler):
-    logging.root.addHandler(handler)
-    yield logging.root
-    logging.root.removeHandler(handler)
-
-
 @pytest.mark.parametrize("level", ["DEBUG", "WARNING", "ERROR", "INFO", "CRITICAL"])
-def test_setup_with_valid_log_levels(root_logger, stdout, level):
+def test_setup_with_valid_log_levels(stdout, level):
     logger = Logger(level=level, stream=stdout, request_id="request id!", another="value")
     msg = "This is a test"
     log_command = {
@@ -55,7 +37,7 @@ def test_setup_with_valid_log_levels(root_logger, stdout, level):
     assert "exception" not in log_dict
 
 
-def test_logging_exception_traceback(root_logger, stdout):
+def test_logging_exception_traceback(stdout):
     logger = Logger(level="DEBUG", stream=stdout, request_id="request id!", another="value")
 
     try:
@@ -69,7 +51,7 @@ def test_logging_exception_traceback(root_logger, stdout):
     assert "exception" in log_dict
 
 
-def test_setup_with_invalid_log_level(root_logger, logger, stdout):
+def test_setup_with_invalid_log_level(stdout):
     with pytest.raises(ValueError) as e:
         Logger(level="not a valid log level")
         assert "Unknown level" in e.value.args[0]
@@ -82,11 +64,7 @@ def check_log_dict(log_dict):
     assert "message" in log_dict
 
 
-def test_setup_with_bad_level_does_not_fail():
-    Logger("DBGG", request_id="request id!", another="value")
-
-
-def test_with_dict_message(root_logger, stdout):
+def test_with_dict_message(stdout):
     logger = Logger(level="DEBUG", stream=stdout)
 
     msg = {"x": "isx"}
@@ -97,7 +75,7 @@ def test_with_dict_message(root_logger, stdout):
     assert msg == log_dict["message"]
 
 
-def test_with_json_message(root_logger, stdout):
+def test_with_json_message(stdout):
     logger = Logger(stream=stdout)
 
     msg = {"x": "isx"}
@@ -108,7 +86,7 @@ def test_with_json_message(root_logger, stdout):
     assert msg == log_dict["message"]
 
 
-def test_with_unserialisable_value_in_message(root_logger, stdout):
+def test_with_unserialisable_value_in_message(stdout):
     logger = Logger(level="DEBUG", stream=stdout)
 
     class X: