Logger

Logger utility

Usage Documentation

Logger

CLASS	DESCRIPTION
Logger	Creates and setups a logger to format statements in JSON.

FUNCTION	DESCRIPTION
log_uncaught_exception_hook	Callback function for sys.excepthook to use Logger to log uncaught exceptions
set_package_logger	Set an additional stream handler, formatter, and log level for aws_lambda_powertools package logger.

Logger

Logger(
    service: str | None = None,
    level: str | int | None = None,
    child: bool = False,
    sampling_rate: float | None = None,
    stream: IO[str] | None = None,
    logger_formatter: PowertoolsFormatter | None = None,
    logger_handler: Handler | None = None,
    log_uncaught_exceptions: bool = False,
    json_serializer: Callable[[dict], str] | None = None,
    json_deserializer: (
        Callable[[dict | str | bool | int | float], str]
        | None
    ) = None,
    json_default: Callable[[Any], Any] | None = None,
    datefmt: str | None = None,
    use_datetime_directive: bool = False,
    log_record_order: list[str] | None = None,
    utc: bool = False,
    use_rfc3339: bool = False,
    serialize_stacktrace: bool = True,
    **kwargs
)

Creates and setups a logger to format statements in JSON.

Includes service name and any additional key=value into logs It also accepts both service name or level explicitly via env vars

Environment variables

POWERTOOLS_SERVICE_NAME : str service name POWERTOOLS_LOG_LEVEL: str logging level (e.g. INFO, DEBUG) POWERTOOLS_LOGGER_SAMPLE_RATE: float sampling rate ranging from 0 to 1, 1 being 100% sampling

PARAMETER	DESCRIPTION
service	service name to be appended in logs, by default "service_undefined" TYPE: str DEFAULT: None
level	The level to set. Can be a string representing the level name: 'DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL' or an integer representing the level value: 10 for 'DEBUG', 20 for 'INFO', 30 for 'WARNING', 40 for 'ERROR', 50 for 'CRITICAL'. by default "INFO" TYPE: str, int optional DEFAULT: None
child	create a child Logger named ., False by default TYPE: bool DEFAULT: False
sampling_rate	sample rate for debug calls within execution context defaults to 0.0 TYPE: float | None DEFAULT: None
stream	valid output for a logging stream, by default sys.stdout TYPE: IO[str] | None DEFAULT: None
logger_formatter	custom logging formatter that implements PowertoolsFormatter TYPE: PowertoolsFormatter | None DEFAULT: None
logger_handler	custom logging handler e.g. logging.FileHandler("file.log") TYPE: Handler | None DEFAULT: None
log_uncaught_exceptions	logs uncaught exception using sys.excepthook See: https://docs.python.org/3/library/sys.html#sys.excepthook TYPE: bool DEFAULT: False

Parameters propagated to LambdaPowertoolsFormatter

json_serializer : Callable, optional function to serialize obj to a JSON formatted str, by default json.dumps json_deserializer : Callable, optional function to deserialize str, bytes, bytearraycontaining a JSON document to a Pythonobj, by default json.loads json_default : Callable, optional function to coerce unserializable values, by defaultstr()` Only used when no custom formatter is set utc : bool, optional set logging timestamp to UTC, by default False to continue to use local time as per stdlib log_record_order : list, optional set order of log keys when logging, by default ["level", "location", "message", "timestamp"]

Example

Setups structured logging in JSON for Lambda functions with explicit service name

>>> from aws_lambda_powertools import Logger
>>> logger = Logger(service="payment")
>>>
>>> def handler(event, context):
        logger.info("Hello")

Setups structured logging in JSON for Lambda functions using env vars

$ export POWERTOOLS_SERVICE_NAME="payment"
$ export POWERTOOLS_LOGGER_SAMPLE_RATE=0.01 # 1% debug sampling
>>> from aws_lambda_powertools import Logger
>>> logger = Logger()
>>>
>>> def handler(event, context):
        logger.info("Hello")

Append payment_id to previously setup logger

>>> from aws_lambda_powertools import Logger
>>> logger = Logger(service="payment")
>>>
>>> def handler(event, context):
        logger.append_keys(payment_id=event["payment_id"])
        logger.info("Hello")

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)

Logging in UTC timezone

>>> # app.py
>>> import logging
>>> from aws_lambda_powertools import Logger
>>>
>>> logger = Logger(service="payment", utc=True)

Brings message as the first key in log statements

>>> # app.py
>>> import logging
>>> from aws_lambda_powertools import Logger
>>>
>>> logger = Logger(service="payment", log_record_order=["message"])

Logging to a file instead of standard output for testing

>>> # app.py
>>> import logging
>>> from aws_lambda_powertools import Logger
>>>
>>> logger = Logger(service="payment", logger_handler=logging.FileHandler("log.json"))

RAISES	DESCRIPTION
InvalidLoggerSamplingRateError	When sampling rate provided is not a float

METHOD	DESCRIPTION
append_context_keys	Context manager to temporarily add logging keys.
clear_state	Removes all custom keys that were appended to the Logger.
get_correlation_id	Gets the correlation_id in the logging json
inject_lambda_context	Decorator to capture Lambda contextual info and inject into logger
set_correlation_id	Sets the correlation_id in the logging json
structure_logs	Sets logging formatting to JSON.

ATTRIBUTE	DESCRIPTION
handlers	List of registered logging handlers TYPE: list[Handler]
registered_formatter	Convenience property to access the first logger formatter TYPE: BasePowertoolsFormatter
registered_handler	Convenience property to access the first logger handler TYPE: Handler

Source code in aws_lambda_powertools/logging/logger.py

def __init__(
    self,
    service: str | None = None,
    level: str | int | None = None,
    child: bool = False,
    sampling_rate: float | None = None,
    stream: IO[str] | None = None,
    logger_formatter: PowertoolsFormatter | None = None,
    logger_handler: logging.Handler | None = None,
    log_uncaught_exceptions: bool = False,
    json_serializer: Callable[[dict], str] | None = None,
    json_deserializer: Callable[[dict | str | bool | int | float], str] | None = None,
    json_default: Callable[[Any], Any] | None = None,
    datefmt: str | None = None,
    use_datetime_directive: bool = False,
    log_record_order: list[str] | None = None,
    utc: bool = False,
    use_rfc3339: bool = False,
    serialize_stacktrace: bool = True,
    **kwargs,
) -> None:
    self.service = resolve_env_var_choice(
        choice=service,
        env=os.getenv(constants.SERVICE_NAME_ENV, "service_undefined"),
    )
    self.sampling_rate = resolve_env_var_choice(
        choice=sampling_rate,
        env=os.getenv(constants.LOGGER_LOG_SAMPLING_RATE),
    )
    self._default_log_keys: dict[str, Any] = {"service": self.service, "sampling_rate": self.sampling_rate}
    self.child = child
    self.logger_formatter = logger_formatter
    self._stream = stream or sys.stdout

    self.log_uncaught_exceptions = log_uncaught_exceptions

    self._is_deduplication_disabled = resolve_truthy_env_var_choice(
        env=os.getenv(constants.LOGGER_LOG_DEDUPLICATION_ENV, "false"),
    )
    self._logger = self._get_logger()
    self.logger_handler = logger_handler or self._get_handler()

    # NOTE: This is primarily to improve UX, so IDEs can autocomplete LambdaPowertoolsFormatter options
    # previously, we masked all of them as kwargs thus limiting feature discovery
    formatter_options = {
        "json_serializer": json_serializer,
        "json_deserializer": json_deserializer,
        "json_default": json_default,
        "datefmt": datefmt,
        "use_datetime_directive": use_datetime_directive,
        "log_record_order": log_record_order,
        "utc": utc,
        "use_rfc3339": use_rfc3339,
        "serialize_stacktrace": serialize_stacktrace,
    }

    self._init_logger(formatter_options=formatter_options, log_level=level, **kwargs)

    if self.log_uncaught_exceptions:
        logger.debug("Replacing exception hook")
        sys.excepthook = functools.partial(log_uncaught_exception_hook, logger=self)

handlers property

handlers: list[Handler]

List of registered logging handlers

Notes

Looking for the first configured handler? Use registered_handler property instead.

registered_formatter property

registered_formatter: BasePowertoolsFormatter

Convenience property to access the first logger formatter

registered_handler property

registered_handler: Handler

Convenience property to access the first logger handler

append_context_keys

append_context_keys(
    **additional_keys: Any,
) -> Generator[None, None, None]

Context manager to temporarily add logging keys.

PARAMETER	DESCRIPTION
**additional_keys	Key-value pairs to include in the log context during the lifespan of the context manager. TYPE: Any DEFAULT: {}

Example

Logging with contextual keys

logger = Logger(service="example_service")
with logger.append_context_keys(user_id="123", operation="process"):
    logger.info("Log with context")
logger.info("Log without context")

Source code in aws_lambda_powertools/logging/logger.py

@contextmanager
def append_context_keys(self, **additional_keys: Any) -> Generator[None, None, None]:
    """
    Context manager to temporarily add logging keys.

    Parameters
    -----------
    **additional_keys: Any
        Key-value pairs to include in the log context during the lifespan of the context manager.

    Example
    --------
    **Logging with contextual keys**

        logger = Logger(service="example_service")
        with logger.append_context_keys(user_id="123", operation="process"):
            logger.info("Log with context")
        logger.info("Log without context")
    """
    with self.registered_formatter.append_context_keys(**additional_keys):
        yield

clear_state

clear_state() -> None

Removes all custom keys that were appended to the Logger.

Source code in aws_lambda_powertools/logging/logger.py

def clear_state(self) -> None:
    """Removes all custom keys that were appended to the Logger."""
    # Clear all custom keys from the formatter
    self.registered_formatter.clear_state()

    # Reset to default keys
    self.structure_logs(**self._default_log_keys)

get_correlation_id

get_correlation_id() -> str | None

Gets the correlation_id in the logging json

RETURNS	DESCRIPTION
(str, optional)	Value for the correlation id

Source code in aws_lambda_powertools/logging/logger.py

def get_correlation_id(self) -> str | None:
    """Gets the correlation_id in the logging json

    Returns
    -------
    str, optional
        Value for the correlation id
    """
    if isinstance(self.registered_formatter, LambdaPowertoolsFormatter):
        return self.registered_formatter.log_format.get("correlation_id")
    return None

inject_lambda_context

inject_lambda_context(
    lambda_handler: AnyCallableT,
    log_event: bool | None = None,
    correlation_id_path: str | None = None,
    clear_state: bool | None = False,
) -> AnyCallableT

inject_lambda_context(
    lambda_handler: None = None,
    log_event: bool | None = None,
    correlation_id_path: str | None = None,
    clear_state: bool | None = False,
) -> Callable[[AnyCallableT], AnyCallableT]

inject_lambda_context(
    lambda_handler: AnyCallableT | None = None,
    log_event: bool | None = None,
    correlation_id_path: str | None = None,
    clear_state: bool | None = False,
) -> Any

Decorator to capture Lambda contextual info and inject into logger

PARAMETER	DESCRIPTION
clear_state	Instructs logger to remove any custom keys previously added TYPE: bool DEFAULT: False
lambda_handler	Method to inject the lambda context TYPE: Callable DEFAULT: None
log_event	Instructs logger to log Lambda Event, by default False TYPE: bool DEFAULT: None
correlation_id_path	Optional JMESPath for the correlation_id TYPE: str | None DEFAULT: None

Environment variables

POWERTOOLS_LOGGER_LOG_EVENT : str instruct logger to log Lambda Event (e.g. "true", "True", "TRUE")

Example

Captures Lambda contextual runtime info (e.g memory, arn, req_id)

from aws_lambda_powertools import Logger

logger = Logger(service="payment")

@logger.inject_lambda_context
def handler(event, context):
    logger.info("Hello")

Captures Lambda contextual runtime info and logs incoming request

from aws_lambda_powertools import Logger

logger = Logger(service="payment")

@logger.inject_lambda_context(log_event=True)
def handler(event, context):
    logger.info("Hello")

RETURNS	DESCRIPTION
decorate	Decorated lambda handler TYPE: Callable

Source code in aws_lambda_powertools/logging/logger.py

def inject_lambda_context(
    self,
    lambda_handler: AnyCallableT | None = None,
    log_event: bool | None = None,
    correlation_id_path: str | None = None,
    clear_state: bool | None = False,
) -> Any:
    """Decorator to capture Lambda contextual info and inject into logger

    Parameters
    ----------
    clear_state : bool, optional
        Instructs logger to remove any custom keys previously added
    lambda_handler : Callable
        Method to inject the lambda context
    log_event : bool, optional
        Instructs logger to log Lambda Event, by default False
    correlation_id_path: str, optional
        Optional JMESPath for the correlation_id

    Environment variables
    ---------------------
    POWERTOOLS_LOGGER_LOG_EVENT : str
        instruct logger to log Lambda Event (e.g. `"true", "True", "TRUE"`)

    Example
    -------
    **Captures Lambda contextual runtime info (e.g memory, arn, req_id)**

        from aws_lambda_powertools import Logger

        logger = Logger(service="payment")

        @logger.inject_lambda_context
        def handler(event, context):
            logger.info("Hello")

    **Captures Lambda contextual runtime info and logs incoming request**

        from aws_lambda_powertools import Logger

        logger = Logger(service="payment")

        @logger.inject_lambda_context(log_event=True)
        def handler(event, context):
            logger.info("Hello")

    Returns
    -------
    decorate : Callable
        Decorated lambda handler
    """

    # If handler is None we've been called with parameters
    # Return a partial function with args filled
    if lambda_handler is None:
        logger.debug("Decorator called with parameters")
        return functools.partial(
            self.inject_lambda_context,
            log_event=log_event,
            correlation_id_path=correlation_id_path,
            clear_state=clear_state,
        )

    log_event = resolve_truthy_env_var_choice(
        env=os.getenv(constants.LOGGER_LOG_EVENT_ENV, "false"),
        choice=log_event,
    )

    @functools.wraps(lambda_handler)
    def decorate(event, context, *args, **kwargs):
        lambda_context = build_lambda_context_model(context)
        cold_start = _is_cold_start()

        if clear_state:
            self.structure_logs(cold_start=cold_start, **lambda_context.__dict__)
        else:
            self.append_keys(cold_start=cold_start, **lambda_context.__dict__)

        if correlation_id_path:
            self.set_correlation_id(
                jmespath_utils.query(envelope=correlation_id_path, data=event),
            )

        if log_event:
            logger.debug("Event received")
            self.info(extract_event_from_common_models(event))

        return lambda_handler(event, context, *args, **kwargs)

    return decorate

set_correlation_id

set_correlation_id(value: str | None) -> None

Sets the correlation_id in the logging json

PARAMETER	DESCRIPTION
value	Value for the correlation id. None will remove the correlation_id TYPE: str

Source code in aws_lambda_powertools/logging/logger.py

def set_correlation_id(self, value: str | None) -> None:
    """Sets the correlation_id in the logging json

    Parameters
    ----------
    value : str, optional
        Value for the correlation id. None will remove the correlation_id
    """
    self.append_keys(correlation_id=value)

structure_logs

structure_logs(
    append: bool = False,
    formatter_options: dict | None = None,
    **keys
) -> None

Sets logging formatting to JSON.

Optionally, it can append keyword arguments to an existing logger, so it is available across future log statements.

Last keyword argument and value wins if duplicated.

PARAMETER	DESCRIPTION
append	append keys provided to logger formatter, by default False TYPE: bool DEFAULT: False
formatter_options	LambdaPowertoolsFormatter options to be propagated, by default {} TYPE: dict DEFAULT: None

Source code in aws_lambda_powertools/logging/logger.py

def structure_logs(self, append: bool = False, formatter_options: dict | None = None, **keys) -> None:
    """Sets logging formatting to JSON.

    Optionally, it can append keyword arguments
    to an existing logger, so it is available across future log statements.

    Last keyword argument and value wins if duplicated.

    Parameters
    ----------
    append : bool, optional
        append keys provided to logger formatter, by default False
    formatter_options : dict, optional
        LambdaPowertoolsFormatter options to be propagated, by default {}
    """
    formatter_options = formatter_options or {}

    # There are 3 operational modes for this method
    ## 1. Register a Powertools for AWS Lambda (Python) Formatter for the first time
    ## 2. Append new keys to the current logger formatter; deprecated in favour of append_keys
    ## 3. Add new keys and discard existing to the registered formatter

    # Mode 1
    log_keys = {**self._default_log_keys, **keys}
    is_logger_preconfigured = getattr(self._logger, LOGGER_ATTRIBUTE_PRECONFIGURED, False)
    if not is_logger_preconfigured:
        formatter = self.logger_formatter or LambdaPowertoolsFormatter(**formatter_options, **log_keys)
        self.registered_handler.setFormatter(formatter)

        # when using a custom Powertools for AWS Lambda (Python) Formatter
        # standard and custom keys that are not Powertools for AWS Lambda (Python) Formatter parameters
        # should be appended and custom keys that might happen to be Powertools for AWS Lambda (Python)
        # Formatter parameters should be discarded this prevents adding them as custom keys, for example,
        # `json_default=<callable>` see https://github.com/aws-powertools/powertools-lambda-python/issues/1263
        custom_keys = {k: v for k, v in log_keys.items() if k not in RESERVED_FORMATTER_CUSTOM_KEYS}
        return self.registered_formatter.append_keys(**custom_keys)

    # Mode 2 (legacy)
    if append:
        # Maintenance: Add deprecation warning for major version
        return self.append_keys(**keys)

    # Mode 3
    self.registered_formatter.clear_state()
    self.registered_formatter.thread_safe_clear_keys()
    self.registered_formatter.append_keys(**log_keys)

log_uncaught_exception_hook

log_uncaught_exception_hook(
    exc_type, exc_value, exc_traceback, logger: Logger
) -> None

Callback function for sys.excepthook to use Logger to log uncaught exceptions

Source code in aws_lambda_powertools/logging/logger.py

def log_uncaught_exception_hook(exc_type, exc_value, exc_traceback, logger: Logger) -> None:
    """Callback function for sys.excepthook to use Logger to log uncaught exceptions"""
    logger.exception(exc_value, exc_info=(exc_type, exc_value, exc_traceback))  # pragma: no cover

set_package_logger

set_package_logger(
    level: str | int = logging.DEBUG,
    stream: IO[str] | None = None,
    formatter: Formatter | None = None,
) -> None

Set an additional stream handler, formatter, and log level for aws_lambda_powertools package logger.

Package log by default is suppressed (NullHandler), this should only used for debugging. This is separate from application Logger class utility

Example

Enables debug logging for Powertools for AWS Lambda (Python) package

>>> aws_lambda_powertools.logging.logger import set_package_logger
>>> set_package_logger()

PARAMETER	DESCRIPTION
level	log level, DEBUG by default TYPE: str | int DEFAULT: DEBUG
stream	log stream, stdout by default TYPE: IO[str] | None DEFAULT: None
formatter	log formatter, "%(asctime)s %(name)s [%(levelname)s] %(message)s" by default TYPE: Formatter | None DEFAULT: None

Source code in aws_lambda_powertools/logging/logger.py

def set_package_logger(
    level: str | int = logging.DEBUG,
    stream: IO[str] | None = None,
    formatter: logging.Formatter | None = None,
) -> None:
    """Set an additional stream handler, formatter, and log level for aws_lambda_powertools package logger.

    **Package log by default is suppressed (NullHandler), this should only used for debugging.
    This is separate from application Logger class utility**

    Example
    -------
    **Enables debug logging for Powertools for AWS Lambda (Python) package**

        >>> aws_lambda_powertools.logging.logger import set_package_logger
        >>> set_package_logger()

    Parameters
    ----------
    level: str, int
        log level, DEBUG by default
    stream: sys.stdout
        log stream, stdout by default
    formatter: logging.Formatter
        log formatter, "%(asctime)s %(name)s [%(levelname)s] %(message)s" by default
    """
    if formatter is None:
        formatter = logging.Formatter("%(asctime)s %(name)s [%(levelname)s] %(message)s")

    if stream is None:
        stream = sys.stdout

    logger = logging.getLogger("aws_lambda_powertools")
    logger.setLevel(level)
    handler = logging.StreamHandler(stream)
    handler.setFormatter(formatter)
    logger.addHandler(handler)