Logging#
The following logging guidelines are best practices discovered through implementing logging services and modules within PyAnsys libraries. Suggestions and improvements are welcomed.
For logging techniques, see Logging HOWTO in the Python documentation. These tutorials are particularly helpful:
Logging overview#
Logging helps to track events occurring in the app. A log record is created for each event. This record contains detailed information about the current app operation. Whenever information must be exposed, displayed, and shared, logging is the way to do it.
Logging is beneficial to both users and app developers. It serves several purposes, including these:
Extracts some valuable data for users to know the status of their work
Tracks the progress and course of app usage
Provides the developer with as much information as possible if an issue happens
The message logged can contain generic information or embed data specific to the
current session. Message content is associated with a severity level, such as INFO,
WARNING, ERROR, and DEBUG. Generally, the severity level indicates the
recipient of the message. For example, an INFO message is directed to the user,
while a DEBUG message is directed to the developer.
Logging best practices#
The logging capabilities in PyAnsys libraries should be built upon Python’s standard
logging library. A PyAnsys library should not replace the standard logging library
but rather provide a way for both it and the PyAnsys library to interact. Subsequent
sections provide best logging practices.
Avoid printing to the console#
A common habit while prototyping a new feature is to print a message into the
command line executable. Instead of using the common print method, you should use a
stream handler
and redirect its content. This allows messages to be filtered based on
their severity level and apply formatting properly. To accomplish this, add a
Boolean argument in the initializer of the logging.Logger class that
specifies how to handle the stream.
Turn on and off handlers#
You might sometimes want to turn off a specific handler, such as a file handler where log messages are written. If so, you must properly close and remove the existing handler. Otherwise, you might be denied file access later when you try to write new log content.
This code snippet shows how to turn off a log handler:
for handler in design_logger.handlers:
if isinstance(handler, logging.FileHandler):
handler.close()
design_logger.removeHandler(handler)
Use app filters#
An app filter shows all its value when the content of a message depends on some conditions. It injects contextual information in the core of the message. This can be used to harmonize message rendering when the app output varies based on the data processed.
Using an app filter requires the creation of a class based on the logging.Filter
class from the logging module and the implementation of its filter()
function. This function contains all modified content to send to the stream:
class AppFilter(logging.Filter):
def __init__(self, destination=None, extra=None):
if not destination:
self._destination = "Global"
if not extra:
self._extra = ""
def filter(self, record):
"""Modify the record sent to the stream.
Parameters
----------
record :
"""
record.destination = self._destination
# This will avoid the extra '::' for Global that does not have any extra info.
if not self._extra:
record.extra = self._extra
else:
record.extra = self._extra + ":"
return True
class CustomLogger(object):
def __init__(self, messenger, level=logging.DEBUG, to_stdout=False):
if to_stdout:
self._std_out_handler = logging.StreamHandler()
self._std_out_handler.setLevel(level)
self._std_out_handler.setFormatter(FORMATTER)
self.global_logger.addHandler(self._std_out_handler)
Use %-formatting for strings#
Although using the f-string for formatting most strings is often recommended, when it comes to logging, using the former %-formatting is preferable. When %-formatting is used, the string is not evaluated at runtime. Instead, it is evaluated only when the message is emitted. If any formatting or evaluation errors occur, they are reported as logging errors and do not halt code.
logger.info("Project %s has been opened.", project.GetName())
App and service logging modules#
PyAnsys libraries use app and service logging modules to extend or expose features from an Ansys app, product, or service, which can be local or remote.
For a PyAnsys library, there are two main loggers that expose or extend a service-based app:
These loggers are customized classes that wrap the logging.Logger
class from the logging module and add specific features to it. This
image shows the logging approach used by PyMAPDL and the scopes
of the global and instance loggers.
You can see the source for a custom PyAnsys logger in the first of the following
collapsible sections and in the pyansys_logging.py
file in the pyansys-dev-guide repository. The second collapsible section shows some unit tests
that show how to use this custom PyAnsys logger:
Example of a custom PyAnsys logger
from copy import copy
from datetime import datetime
import logging
from logging import CRITICAL, DEBUG, ERROR, INFO, WARN
import sys
# Default configuration
LOG_LEVEL = logging.DEBUG
FILE_NAME = "PyProject.log"
# Formatting
STDOUT_MSG_FORMAT = (
"%(levelname)s - %(instance_name)s - %(module)s - %(funcName)s - %(message)s"
)
FILE_MSG_FORMAT = STDOUT_MSG_FORMAT
DEFAULT_STDOUT_HEADER = """
LEVEL - INSTANCE NAME - MODULE - FUNCTION - MESSAGE
"""
DEFAULT_FILE_HEADER = DEFAULT_STDOUT_HEADER
NEW_SESSION_HEADER = f"""
===============================================================================
NEW SESSION - {datetime.now().strftime("%m/%d/%Y, %H:%M:%S")}
==============================================================================="""
string_to_loglevel = {
"DEBUG": DEBUG,
"INFO": INFO,
"WARN": WARN,
"WARNING": WARN,
"ERROR": ERROR,
"CRITICAL": CRITICAL,
}
class InstanceCustomAdapter(logging.LoggerAdapter):
"""Keeps the reference to a product instance name dynamic.
If you use the standard approach, which is supplying ``extra`` input
to the logger, you would need to keep inputting product instances
every time a log is created.
Using adapters, you just need to specify the product instance that you refer
to once.
"""
# level is kept for compatibility with ``suppress_logging``,
# but it does nothing.
level = None
file_handler = None
stdout_handler = None
def __init__(self, logger, extra=None):
self.logger = logger
self.extra = extra
self.file_handler = logger.file_handler
self.std_out_handler = logger.std_out_handler
def process(self, msg, kwargs):
kwargs["extra"] = {}
# These are the extra parameters sent to log
# here self.extra is the argument pass to the log records.
kwargs["extra"]["instance_name"] = self.extra.get_name()
return msg, kwargs
def log_to_file(self, filename=FILE_NAME, level=LOG_LEVEL):
"""Add file handler to logger.
Parameters
----------
filename : str, optional
Name of the file where the logs are recorded. By default
``PyProject.log``
level : str, optional
Level of logging, for example ``'DEBUG'``. By default
``logging.DEBUG``.
"""
self.logger = add_file_handler(
self.logger, filename=filename, level=level, write_headers=True
)
self.file_handler = self.logger.file_handler
def log_to_stdout(self, level=LOG_LEVEL):
"""Add standard output handler to the logger.
Parameters
----------
level : str, optional
Level of logging record. By default ``logging.DEBUG``.
"""
if self.std_out_handler:
raise Exception("Stdout logger already defined.")
self.logger = add_stdout_handler(self.logger, level=level)
self.std_out_handler = self.logger.std_out_handler
def setLevel(self, level="DEBUG"):
"""Change the log level of the object and the attached handlers."""
self.logger.setLevel(level)
for each_handler in self.logger.handlers:
each_handler.setLevel(level)
self.level = level
class PyAnsysPercentStyle(logging.PercentStyle):
def __init__(self, fmt, *, defaults=None):
self._fmt = fmt or self.default_format
self._defaults = defaults
def _format(self, record):
defaults = self._defaults
if defaults:
values = defaults | record.__dict__
else:
values = record.__dict__
# Here you can make any changes that you want in the record. For
# example, adding a key.
# You could create an ``if`` here if you want conditional formatting, and even
# change the record.__dict__.
# If you don't want to create conditional fields, it is fine to keep
# the same MSG_FORMAT for all of them.
# For the case of logging exceptions to the logger.
values.setdefault("instance_name", "")
return STDOUT_MSG_FORMAT % values
class PyProjectFormatter(logging.Formatter):
"""Customized ``Formatter`` class used to overwrite the defaults format styles."""
def __init__(
self,
fmt=STDOUT_MSG_FORMAT,
datefmt=None,
style="%",
validate=True,
defaults=None,
):
if sys.version_info[1] < 8:
super().__init__(fmt, datefmt, style)
else:
# 3.8: The validate parameter was added
super().__init__(fmt, datefmt, style, validate)
self._style = PyAnsysPercentStyle(fmt, defaults=defaults) # overwriting
class InstanceFilter(logging.Filter):
"""Ensures that instance_name record always exists."""
def filter(self, record):
if not hasattr(record, "instance_name"):
record.instance_name = ""
return True
class Logger:
"""Logger used for each PyProject session.
This class lets you add a handler to a file or standard output.
Parameters
----------
level : int, optional
Logging level to filter the message severity allowed in the logger.
The default is ``logging.DEBUG``.
to_file : bool, optional
Write log messages to a file. The default is ``False``.
to_stdout : bool, optional
Write log messages into the standard output. The
default is ``True``.
filename : str, optional
Name of the file where log messages are written to.
The default is ``None``.
"""
file_handler = None
std_out_handler = None
_level = logging.DEBUG
_instances = {}
def __init__(
self,
level=logging.DEBUG,
to_file=False,
to_stdout=True,
filename=FILE_NAME,
cleanup=True,
):
"""Initialize Logger class."""
self.logger = logging.getLogger(
"pyproject_global"
) # Creating default main logger.
self.logger.addFilter(InstanceFilter())
self.logger.setLevel(level)
self.logger.propagate = True
self.level = self.logger.level # TODO: TO REMOVE
# Writing logging methods.
self.debug = self.logger.debug
self.info = self.logger.info
self.warning = self.logger.warning
self.error = self.logger.error
self.critical = self.logger.critical
self.log = self.logger.log
if to_file or filename != FILE_NAME:
# We record to file.
self.log_to_file(filename=filename, level=level)
if to_stdout:
self.log_to_stdout(level=level)
self.add_handling_uncaught_expections(
self.logger
) # Using logger to record unhandled exceptions.
self.cleanup = cleanup
def log_to_file(self, filename=FILE_NAME, level=LOG_LEVEL):
"""Add file handler to logger.
Parameters
----------
filename : str, optional
Name of the file where the logs are recorded. By default FILE_NAME
level : str, optional
Level of logging. E.x. 'DEBUG'. By default LOG_LEVEL
"""
self = add_file_handler(
self, filename=filename, level=level, write_headers=True
)
def log_to_stdout(self, level=LOG_LEVEL):
"""Add standard output handler to the logger.
Parameters
----------
level : str, optional
Level of logging record. By default LOG_LEVEL
"""
self = add_stdout_handler(self, level=level)
def setLevel(self, level="DEBUG"):
"""Change the log level of the object and the attached handlers."""
self.logger.setLevel(level)
for each_handler in self.logger.handlers:
each_handler.setLevel(level)
self._level = level
def _make_child_logger(self, suffix, level):
"""Create a child logger.
Create a child logger either using ``getChild`` or copying
attributes between ``pyproject_global`` logger and the new
one.
"""
logger = logging.getLogger(suffix)
logger.std_out_handler = None
logger.file_handler = None
if self.logger.hasHandlers:
for each_handler in self.logger.handlers:
new_handler = copy(each_handler)
if each_handler == self.file_handler:
logger.file_handler = new_handler
elif each_handler == self.std_out_handler:
logger.std_out_handler = new_handler
if level:
# The logger handlers are copied and changed the
# loglevel if the specified log level is lower
# than the one of the global.
if each_handler.level > string_to_loglevel[level.upper()]:
new_handler.setLevel(level)
logger.addHandler(new_handler)
if level:
if isinstance(level, str):
level = string_to_loglevel[level.upper()]
logger.setLevel(level)
else:
logger.setLevel(self.logger.level)
logger.propagate = True
return logger
def add_child_logger(self, suffix, level=None):
"""Add a child logger to the main logger.
This logger is more general than an instance logger which is designed
to track the state of the application instances.
If the logging level is in the arguments, a new logger with a
reference to the ``_global`` logger handlers is created
instead of a child.
Parameters
----------
suffix : str
Name of the logger.
level : str
Level of logging
Returns
-------
logging.logger
Logger class.
"""
name = self.logger.name + "." + suffix
self._instances[name] = self._make_child_logger(self, name, level)
return self._instances[name]
def _add_product_instance_logger(self, name, product_instance, level):
if isinstance(name, str):
instance_logger = InstanceCustomAdapter(
self._make_child_logger(name, level), product_instance
)
elif isinstance(name, None):
instance_logger = InstanceCustomAdapter(
self._make_child_logger("NO_NAMED_YET", level), product_instance
)
else:
raise TypeError(
f"``name`` parameter must be a string or None, not f{type(name)}"
)
return instance_logger
def add_instance_logger(self, name, product_instance, level=None):
"""Create a logger for an application instance.
This instance logger is a logger with an adapter which add the
contextual information such as <product/service> instance
name. This logger is returned and you can use it to log events
as a normal logger. It is also stored in the ``_instances``
attribute.
Parameters
----------
name : str
Name for the new logger
product_instance : ansys.product.service.module.ProductClass
Class instance. This must contain the attribute ``name``.
Returns
-------
InstanceCustomAdapter
Logger adapter customized to add additional information to
the logs. You can use this class to log events in the
same way you would with a logger class.
Raises
------
TypeError
You can only input strings as ``name`` to this method.
"""
count_ = 0
new_name = name
while new_name in logging.root.manager.__dict__.keys():
count_ += 1
new_name = name + "_" + str(count_)
self._instances[new_name] = self._add_product_instance_logger(
new_name, product_instance, level
)
return self._instances[new_name]
def __getitem__(self, key):
if key in self._instances.keys():
return self._instances[key]
else:
raise KeyError(f"There are no instances with name {key}")
def add_handling_uncaught_expections(self, logger):
"""This just redirects the output of an exception to the logger."""
def handle_exception(exc_type, exc_value, exc_traceback):
if issubclass(exc_type, KeyboardInterrupt):
sys.__excepthook__(exc_type, exc_value, exc_traceback)
return
logger.critical(
"Uncaught exception", exc_info=(exc_type, exc_value, exc_traceback)
)
sys.excepthook = handle_exception
def __del__(self):
"""Close the logger and all its handlers."""
self.logger.debug("Collecting logger")
if self.cleanup:
try:
for handler in self.logger.handlers:
handler.close()
self.logger.removeHandler(handler)
except Exception as e:
try:
if self.logger is not None:
self.logger.error("The logger was not deleted properly.")
except Exception:
pass
else:
self.logger.debug("Collecting but not exiting due to 'cleanup = False'")
def add_file_handler(logger, filename=FILE_NAME, level=LOG_LEVEL, write_headers=False):
"""Add a file handler to the input.
Parameters
----------
logger : logging.Logger or logging.Logger
Logger where to add the file handler.
filename : str, optional
Name of the output file. By default FILE_NAME
level : str, optional
Level of log recording. By default LOG_LEVEL
write_headers : bool, optional
Record the headers to the file. By default ``False``.
Returns
-------
logger
Return the logger or Logger object.
"""
file_handler = logging.FileHandler(filename)
file_handler.setLevel(level)
file_handler.setFormatter(logging.Formatter(FILE_MSG_FORMAT))
if isinstance(logger, Logger):
logger.file_handler = file_handler
logger.logger.addHandler(file_handler)
elif isinstance(logger, logging.Logger):
logger.file_handler = file_handler
logger.addHandler(file_handler)
if write_headers:
file_handler.stream.write(NEW_SESSION_HEADER)
file_handler.stream.write(DEFAULT_FILE_HEADER)
return logger
def add_stdout_handler(logger, level=LOG_LEVEL, write_headers=False):
"""Add a stream handler to the logger.
Parameters
----------
logger : logging.Logger or logging.Logger
Logger where to add the stream handler.
level : str, optional
Level of log recording. By default ``logging.DEBUG``.
write_headers : bool, optional
Record the headers to the stream. By default ``False``.
Returns
-------
logger
The logger or Logger object.
"""
std_out_handler = logging.StreamHandler(sys.stdout)
std_out_handler.setLevel(level)
std_out_handler.setFormatter(PyProjectFormatter(STDOUT_MSG_FORMAT))
if isinstance(logger, Logger):
logger.std_out_handler = std_out_handler
logger.logger.addHandler(std_out_handler)
elif isinstance(logger, logging.Logger):
logger.addHandler(std_out_handler)
if write_headers:
std_out_handler.stream.write(DEFAULT_STDOUT_HEADER)
return logger
How to use the PyAnsys custom logger
import io
import logging
import os
import sys
import weakref
import pyansys_logging
def test_default_logger():
"""Create a logger with default options.
Only stdout logger must be used."""
capture = CaptureStdOut()
with capture:
test_logger = pyansys_logging.Logger()
test_logger.info("Test stdout")
assert (
"INFO - - test_pyansys_logging - test_default_logger - Test stdout"
in capture.content
)
# File handlers are not activated.
assert os.path.exists(os.path.exists(os.path.join(os.getcwd(), "PyProject.log")))
def test_level_stdout():
"""Create a logger with default options.
Only stdout logger must be used."""
capture = CaptureStdOut()
with capture:
test_logger = pyansys_logging.Logger(level=logging.INFO)
test_logger.debug("Debug stdout with level=INFO")
test_logger.info("Info stdout with level=INFO")
test_logger.warning("Warning stdout with level=INFO")
test_logger.error("Error stdout with level=INFO")
test_logger.critical("Critical stdout with level=INFO")
# Modify the level
test_logger.setLevel(level=logging.WARNING)
test_logger.debug("Debug stdout with level=WARNING")
test_logger.info("Info stdout with level=WARNING")
test_logger.warning("Warning stdout with level=WARNING")
test_logger.error("Error stdout with level=WARNING")
test_logger.critical("Critical stdout with level=WARNING")
# level=INFO
assert (
"DEBUG - - test_pyansys_logging - test_level_stdout - Debug stdout with level=INFO"
not in capture.content
)
assert (
"INFO - - test_pyansys_logging - test_level_stdout - Info stdout with level=INFO"
in capture.content
)
assert (
"WARNING - - test_pyansys_logging - test_level_stdout - Warning stdout with level=INFO"
in capture.content
)
assert (
"ERROR - - test_pyansys_logging - test_level_stdout - Error stdout with level=INFO"
in capture.content
)
assert (
"CRITICAL - - test_pyansys_logging - test_level_stdout - Critical stdout with level=INFO"
in capture.content
)
# level=WARNING
assert (
"INFO - - test_pyansys_logging - test_level_stdout - Info stdout with level=WARNING"
not in capture.content
)
assert (
"WARNING - - test_pyansys_logging - test_level_stdout - Warning stdout with level=WARNING"
in capture.content
)
assert (
"ERROR - - test_pyansys_logging - test_level_stdout - Error stdout with level=WARNING"
in capture.content
)
assert (
"CRITICAL - - test_pyansys_logging - test_level_stdout - Critical stdout with level=WARNING" # noqa: E501
in capture.content
)
# File handlers are not activated.
assert os.path.exists(os.path.exists(os.path.join(os.getcwd(), "PyProject.log")))
def test_file_handlers(tmpdir):
"""Activate a file handler different from `PyProject.log`."""
file_logger = tmpdir.mkdir("sub").join("test_logger.txt")
test_logger = pyansys_logging.Logger(to_file=True, filename=file_logger)
test_logger.info("Test Misc File")
with open(file_logger, "r") as f:
content = f.readlines()
assert os.path.exists(
file_logger
) # The file handler is not the default PyProject.Log
assert len(content) == 6
assert "NEW SESSION" in content[2]
assert (
"==============================================================================="
in content[3]
)
assert "LEVEL - INSTANCE NAME - MODULE - FUNCTION - MESSAGE" in content[4]
assert (
"INFO - - test_pyansys_logging - test_file_handlers - Test Misc File"
in content[5]
)
# Delete the logger and its file handler.
test_logger_ref = weakref.ref(test_logger)
del test_logger
assert test_logger_ref() is None
class CaptureStdOut:
"""Capture standard output with a context manager."""
def __init__(self):
self._stream = io.StringIO()
def __enter__(self):
sys.stdout = self._stream
def __exit__(self, type, value, traceback):
sys.stdout = sys.__stdout__
@property
def content(self):
"""Return the captured content."""
return self._stream.getvalue()
Global logger#
A global logger named py*_global is created when importing
ansys.product.service (ansys.product.service.__init__). This logger
does not track instances but rather is used globally. Consequently, its use
is recommended for most scenarios, especially those where simple modules
or classes are involved.
For example, if you intend to log the initialization of a library or module, import the global logger at the top of your script or module:
from ansys.product.service import LOG
If the default name of the global logger is in conflict with the name of another logger, rename it:
from ansys.product.service import LOG as logger
The default logging level of the global logger is ERROR (logging.ERROR).
You can change the output to a different error level like this:
LOG.logger.setLevel("DEBUG")
LOG.file_handler.setLevel("DEBUG") # if present
LOG.stdout_handler.setLevel("DEBUG") # if present
Alternatively, to ensure that all handlers are set to the desired log level, use this approach:
LOG.setLevel("DEBUG")
By default, the global logger does not log to a file. However, you can enable logging to both a file and the standard output by adding a file handler:
import os
file_path = os.path.join(os.getcwd(), "pylibrary.log")
LOG.log_to_file(file_path)
If you want to change the characteristics of the global logger from the beginning of
the execution, you must edit the __init__ file in the directory of your
library.
To log using the global logger, simply call the desired method as a normal logger:
>>> import logging
>>> from ansys.mapdl.core.logging import Logger
>>> LOG = Logger(level=logging.DEBUG, to_file=False, to_stdout=True)
>>> LOG.debug("This is LOG debug message.")
| Level | Instance | Module | Function | Message
|----------|------------|--------------|-------------|---------------------------
| DEBUG | | __init__ | <module> | This is LOG debug message.
Instance logger#
An instance logger is created every time that the _MapdlCore class is
instantiated. Using this instance logger is recommended when using the pool
library or when using multiple instances of MAPDL. The main feature of the instance
logger is that it tracks each instance and includes the instance name when logging.
The names of instances are unique. For example, when using the MAPDL gRPC
version, the instance name includes the IP and port of the corresponding instance,
making the logger unique.
You can access instance loggers in two places:
_MapdlCore._logfor backward compatibilityLOG._instances, which is a field of thedictdata type with a key that is the name of the created logger
These instance loggers inherit from the pymapdl_global output handlers and
logging level unless otherwise specified. An instance logger works similarly to
the global logger. If you want to add a file handler, use the log_to_file
method. If you want to change the log level, use the logging.Logger.setLevel()
method.
This code snippet shows how to use an instance logger:
>>> from ansys.mapdl.core import launch_mapdl
>>> mapdl = launch_mapdl()
>>> mapdl._log.info("This is an useful message")
| Level | Instance | Module | Function | Message
|----------|-----------------|----------|-------------|--------------------------
| INFO | 127.0.0.1:50052 | test | <module> | This is an useful message
Ansys product loggers#
An Ansys product, due to its architecture, can have several loggers. The
logging library supports working with a finite number of loggers. The
logging.getLogger() factory function helps to access each logger by its name. In
addition to name mappings, a hierarchy can be established to structure the
loggers’ parenting and their connections.
For example, if an Ansys product is using a pre-existing custom logger encapsulated inside the product itself, the PyAnsys library benefits from exposing it through the standard Python tools. You should use the standard library as much as possible. It facilitates every contribution to the PyAnsys library, both external and internal, by exposing common tools that are widely adopted. Each developer is able to operate quickly and autonomously. The project takes advantage of the entire set of features exposed in the standard logger and all the upcoming improvements.
Custom log handlers#
You might need to catch Ansys product messages and redirect them to another logger. For example, Ansys Electronics Desktop (AEDT) has its own internal logger called the message manager, which has three main destinations:
Global which is for the entire project manager
Project, which is related to the project
Design, which is related to the design, making it the most specific destination of the three loggers
The message manager does not use the standard Python logging module, which
can be a problem when exporting messages and data from it to a common tool.
In most cases, it is easier to work with the standard Python module to extract
data. To overcome this AEDT limitation, you must wrap the existing message
manager into a logger based on the standard logging library:
The wrapper implementation is essentially a custom handler based on a
class inherited from the logging.Handler class. The initializer
of this class requires the message manager to be passed as an argument to link the standard
logging service with the AEDT message manager:
class LogHandler(logging.Handler):
def __init__(self, internal_app_messenger, log_destination, level=logging.INFO):
logging.Handler.__init__(self, level)
# destination is used if when the internal message manager
# is made of several different logs. Otherwise it is not relevant.
self.destination = log_destination
self.messenger = internal_app_messenger
def emit(self, record):
pass
The purpose of the logging.Handler class is to send log messages in the
AEDT logging stream. One of the mandatory actions is to overwrite the emit()
function. This function operates as a proxy, dispatching all log messages to the
message manager. Based on the record level, the message is sent to the appropriate
log level, such as INFO, ERROR, or DEBUG, into the message manager to
fit the level provided by the Ansys product. As a reminder, the record is an object
containing all kind of information related to the event logged.
This custom handler is use in the new logger instance (the one based on the
logging library). To avoid any conflict or message duplication, before adding
a handler on any logger, verify if an appropriate handler is already available.