logging — Logging facility for Python¶Source code: Lib/logging/__init__.py
This module defines functions and classes which implement a flexible event logging system for applications and libraries.
The key benefit of having the logging API provided by a standard library module is that all Python modules can participate in logging, so your application log can include your own messages integrated with messages from third-party modules.
Here’s a simple example of idiomatic usage:
# myapp.py
import logging
import mylib
logger = logging.getLogger(__name__)
def main():
logging.basicConfig(filename='myapp.log', level=logging.INFO)
logger.info('Started')
mylib.do_something()
logger.info('Finished')
if __name__ == '__main__':
main()
# mylib.py
import logging
logger = logging.getLogger(__name__)
def do_something():
logger.info('Doing something')
If you run myapp.py, you should see this in myapp.log:
INFO:__main__:Started
INFO:mylib:Doing something
INFO:__main__:Finished
The key feature of this idiomatic usage is that the majority of code is simply
creating a module level logger with getLogger(__name__), and using that
logger to do any needed logging. This is concise, while allowing downstream
code fine-grained control if needed. Logged messages to the module-level logger
get forwarded to handlers of loggers in higher-level modules, all the way up to
the highest-level logger known as the root logger; this approach is known as
hierarchical logging.
For logging to be useful, it needs to be configured: setting the levels and
destinations for each logger, potentially changing how specific modules log,
often based on command-line arguments or application configuration. In most
cases, like the one above, only the root logger needs to be so configured, since
all the lower level loggers at module level eventually forward their messages to
its handlers. basicConfig() provides a quick way to configure
the root logger that handles many use cases.
The module provides a lot of functionality and flexibility. If you are unfamiliar with logging, the best way to get to grips with it is to view the tutorials (see the links above and on the right).
The basic classes defined by the module, together with their attributes and methods, are listed in the sections below.
Loggers expose the interface that application code directly uses.
Handlers send the log records (created by loggers) to the appropriate destination.
Filters provide a finer grained facility for determining which log records to output.
Formatters specify the layout of log records in the final output.
Loggers have the following attributes and methods. Note that Loggers should
NEVER be instantiated directly, but always through the module-level function
logging.getLogger(name). Multiple calls to getLogger() with the same
name will always return a reference to the same Logger object.
The name is potentially a period-separated hierarchical value, like
foo.bar.baz (though it could also be just plain foo, for example).
Loggers that are further down in the hierarchical list are children of loggers
higher up in the list. For example, given a logger with a name of foo,
loggers with names of foo.bar, foo.bar.baz, and foo.bam are all
descendants of foo. In addition, all loggers are descendants of the root
logger. The logger name hierarchy is analogous to the Python package hierarchy,
and identical to it if you organise your loggers on a per-module basis using
the recommended construction logging.getLogger(__name__). That’s because
in a module, __name__ is the module’s name in the Python package namespace.
This is the logger’s name, and is the value that was passed to getLogger()
to obtain the logger.
Note
This attribute should be treated as read-only.
The threshold of this logger, as set by the setLevel() method.
Note
Do not set this attribute directly - always use setLevel(),
which has checks for the level passed to it.
The parent logger of this logger. It may change based on later instantiation of loggers which are higher up in the namespace hierarchy.
Note
This value should be treated as read-only.
If this attribute evaluates to true, events logged to this logger will be passed to the handlers of higher level (ancestor) loggers, in addition to any handlers attached to this logger. Messages are passed directly to the ancestor loggers’ handlers - neither the level nor filters of the ancestor loggers in question are considered.
If this evaluates to false, logging messages are not passed to the handlers of ancestor loggers.
Spelling it out with an example: If the propagate attribute of the logger named
A.B.C evaluates to true, any event logged to A.B.C via a method call such as
logging.getLogger('A.B.C').error(...) will [subject to passing that logger’s
level and filter settings] be passed in turn to any handlers attached to loggers
named A.B, A and the root logger, after first being passed to any handlers
attached to A.B.C. If any logger in the chain A.B.C, A.B, A has its
propagate attribute set to false, then that is the last logger whose handlers
are offered the event to handle, and propagation stops at that point.
The constructor sets this attribute to True.
Note
If you attach a handler to a logger and one or more of its
ancestors, it may emit the same record multiple times. In general, you
should not need to attach a handler to more than one logger - if you just
attach it to the appropriate logger which is highest in the logger
hierarchy, then it will see all events logged by all descendant loggers,
provided that their propagate setting is left set to True. A common
scenario is to attach handlers only to the root logger, and to let
propagation take care of the rest.
The list of handlers directly attached to this logger instance.
Note
This attribute should be treated as read-only; it is normally changed via
the addHandler() and removeHandler() methods, which use locks to ensure
thread-safe operation.
This attribute disables handling of any events. It is set to False in the
initializer, and only changed by logging configuration code.
Note
This attribute should be treated as read-only.
Sets the threshold for this logger to level. Logging messages which are less severe than level will be ignored; logging messages which have severity level or higher will be emitted by whichever handler or handlers service this logger, unless a handler’s level has been set to a higher severity level than level.
When a logger is created, the level is set to NOTSET (which causes
all messages to be processed when the logger is the root logger, or delegation
to the parent when the logger is a non-root logger). Note that the root logger
is created with level WARNING.
The term ‘delegation to the parent’ means that if a logger has a level of NOTSET, its chain of ancestor loggers is traversed until either an ancestor with a level other than NOTSET is found, or the root is reached.
If an ancestor is found with a level other than NOTSET, then that ancestor’s level is treated as the effective level of the logger where the ancestor search began, and is used to determine how a logging event is handled.
If the root is reached, and it has a level of NOTSET, then all messages will be processed. Otherwise, the root’s level will be used as the effective level.
See Logging Levels for a list of levels.
Changed in version 3.2: The level parameter now accepts a string representation of the
level such as ‘INFO’ as an alternative to the integer constants
such as INFO. Note, however, that levels are internally stored
as integers, and methods such as e.g. getEffectiveLevel() and
isEnabledFor() will return/expect to be passed integers.
Indicates if a message of severity level would be processed by this logger.
This method checks first the module-level level set by
logging.disable(level) and then the logger’s effective level as determined
by getEffectiveLevel().
Indicates the effective level for this logger. If a value other than
NOTSET has been set using setLevel(), it is returned. Otherwise,
the hierarchy is traversed towards the root until a value other than
NOTSET is found, and that value is returned. The value returned is
an integer, typically one of logging.DEBUG, logging.INFO
etc.
Returns a logger which is a descendant to this logger, as determined by the suffix.
Thus, logging.getLogger('abc').getChild('def.ghi') would return the same
logger as would be returned by logging.getLogger('abc.def.ghi'). This is a
convenience method, useful when the parent logger is named using e.g. __name__
rather than a literal string.
Added in version 3.2.
Returns a set of loggers which are immediate children of this logger. So for
example logging.getLogger().getChildren() might return a set containing
loggers named foo and bar, but a logger named foo.bar wouldn’t be
included in the set. Likewise, logging.getLogger('foo').getChildren() might
return a set including a logger named foo.bar, but it wouldn’t include one
named foo.bar.baz.
Added in version 3.12.
Logs a message with level DEBUG on this logger. The msg is the
message format string, and the args are the arguments which are merged into
msg using the string formatting operator. (Note that this means that you can
use keywords in the format string, together with a single dictionary argument.)
No % formatting operation is performed on msg when no args are supplied.
There are four keyword arguments in kwargs which are inspected: exc_info, stack_info, stacklevel and extra.
If exc_info does not evaluate as false, it causes exception information to be
added to the logging message. If an exception tuple (in the format returned by
sys.exc_info()) or an exception instance is provided, it is used;
otherwise, sys.exc_info() is called to get the exception information.
The second optional keyword argument is stack_info, which defaults to
False. If true, stack information is added to the logging
message, including the actual logging call. Note that this is not the same
stack information as that displayed through specifying exc_info: The
former is stack frames from the bottom of the stack up to the logging call
in the current thread, whereas the latter is information about stack frames
which have been unwound, following an exception, while searching for
exception handlers.
You can specify stack_info independently of exc_info, e.g. to just show how you got to a certain point in your code, even when no exceptions were raised. The stack frames are printed following a header line which says:
Stack (most recent call last):
This mimics the Traceback (most recent call last): which is used when
displaying exception frames.
The third optional keyword argument is stacklevel, which defaults to 1.
If greater than 1, the corresponding number of stack frames are skipped
when computing the line number and function name set in the LogRecord
created for the logging event. This can be used in logging helpers so that
the function name, filename and line number recorded are not the information
for the helper function/method, but rather its caller. The name of this
parameter mirrors the equivalent one in the warnings module.
The fourth keyword argument is extra which can be used to pass a
dictionary which is used to populate the __dict__ of the
LogRecord
created for the logging event with user-defined attributes. These custom
attributes can then be used as you like. For example, they could be
incorporated into logged messages. For example:
FORMAT = '%(asctime)s %(clientip)-15s %(user)-8s %(message)s'
logging.basicConfig(format=FORMAT)
d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
logger = logging.getLogger('tcpserver')
logger.warning('Protocol problem: %s', 'connection reset', extra=d)
would print something like
2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
The keys in the dictionary passed in extra should not clash with the keys used by the logging system. (See the section on LogRecord attributes for more information on which keys are used by the logging system.)
If you choose to use these attributes in logged messages, you need to exercise
some care. In the above example, for instance, the Formatter has been
set up with a format string which expects ‘clientip’ and ‘user’ in the attribute
dictionary of the LogRecord. If these are missing, the message will
not be logged because a string formatting exception will occur. So in this case,
you always need to pass the extra dictionary with these keys.
While this might be annoying, this feature is intended for use in specialized
circumstances, such as multi-threaded servers where the same code executes in
many contexts, and interesting conditions which arise are dependent on this
context (such as remote client IP address and authenticated user name, in the
above example). In such circumstances, it is likely that specialized
Formatters would be used with particular Handlers.
If no handler is attached to this logger (or any of its ancestors,
taking into account the relevant Logger.propagate attributes),
the message will be sent to the handler set on lastResort.
Changed in version 3.2: The stack_info parameter was added.
Changed in version 3.5: The exc_info parameter can now accept exception instances.
Changed in version 3.8: The stacklevel parameter was added.
Logs a message with level INFO on this logger. The arguments are
interpreted as for debug().
Logs a message with level WARNING on this logger. The arguments are
interpreted as for debug().
Note
There is an obsolete method warn which is functionally
identical to warning. As warn is deprecated, please do not use
it - use warning instead.
Logs a message with level ERROR on this logger. The arguments are
interpreted as for debug().
Logs a message with level CRITICAL on this logger. The arguments are
interpreted as for debug().
Logs a message with integer level level on this logger. The other arguments are
interpreted as for debug().
Logs a message with level ERROR on this logger. The arguments are
interpreted as for debug(). Exception info is added to the logging
message. This method should only be called from an exception handler.
Adds the specified filter filter to this logger.
Removes the specified filter filter from this logger.
Apply this logger’s filters to the record and return True if the
record is to be processed. The filters are consulted in turn, until one of
them returns a false value. If none of them return a false value, the record
will be processed (passed to handlers). If one returns a false value, no
further processing of the record occurs.
Adds the specified handler hdlr to this logger.
Removes the specified handler hdlr from this logger.
Finds the caller’s source filename and line number. Returns the filename, line
number, function name and stack information as a 4-element tuple. The stack
information is returned as None unless stack_info is True.
The stacklevel parameter is passed from code calling the debug()
and other APIs. If greater than 1, the excess is used to skip stack frames
before determining the values to be returned. This will generally be useful
when calling logging APIs from helper/wrapper code, so that the information
in the event log refers not to the helper/wrapper code, but to the code that
calls it.
Handles a record by passing it to all handlers associated with this logger and
its ancestors (until a false value of propagate is found). This method is used
for unpickled records received from a socket, as well as those created locally.
Logger-level filtering is applied using filter().
This is a factory method which can be overridden in subclasses to create
specialized LogRecord instances.
Checks to see if this logger has any handlers configured. This is done by
looking for handlers in this logger and its parents in the logger hierarchy.
Returns True if a handler was found, else False. The method stops searching
up the hierarchy whenever a logger with the ‘propagate’ attribute set to
false is found - that will be the last logger which is checked for the
existence of handlers.
Added in version 3.2.
Changed in version 3.7: Loggers can now be pickled and unpickled.
The numeric values of logging levels are given in the following table. These are primarily of interest if you want to define your own levels, and need them to have specific values relative to the predefined levels. If you define a level with the same numeric value, it overwrites the predefined value; the predefined name is lost.
Level |
Numeric value |
What it means / When to use it |
|---|---|---|
|
0 |
When set on a logger, indicates that
ancestor loggers are to be consulted
to determine the effective level.
If that still resolves to
|
|
10 |
Detailed information, typically only of interest to a developer trying to diagnose a problem. |
|
20 |
Confirmation that things are working as expected. |
|
30 |
An indication that something unexpected happened, or that a problem might occur in the near future (e.g. ‘disk space low’). The software is still working as expected. |
|
40 |
Due to a more serious problem, the software has not been able to perform some function. |
|
50 |
A serious error, indicating that the program itself may be unable to continue running. |
Handlers have the following attributes and methods. Note that Handler
is never instantiated directly; this class acts as a base for more useful
subclasses. However, the __init__() method in subclasses needs to call
Handler.__init__().
Initializes the Handler instance by setting its level, setting the list
of filters to the empty list and creating a lock (using createLock()) for
serializing access to an I/O mechanism.
Initializes a thread lock which can be used to serialize access to underlying I/O functionality which may not be threadsafe.
Acquires the thread lock created with createLock().
Sets the threshold for this handler to level. Logging messages which are
less severe than level will be ignored. When a handler is created, the
level is set to NOTSET (which causes all messages to be
processed).
See Logging Levels for a list of levels.
Changed in version 3.2: The level parameter now accepts a string representation of the
level such as ‘INFO’ as an alternative to the integer constants
such as INFO.
Sets the formatter for this handler to fmt.
The fmt argument must be a Formatter instance or None.
Adds the specified filter filter to this handler.
Removes the specified filter filter from this handler.
Apply this handler’s filters to the record and return True if the
record is to be processed. The filters are consulted in turn, until one of
them returns a false value. If none of them return a false value, the record
will be emitted. If one returns a false value, the handler will not emit the
record.
Ensure all logging output has been flushed. This version does nothing and is intended to be implemented by subclasses.
Tidy up any resources used by the handler. This version does no output but removes the handler from an internal map of handlers, which is used for handler lookup by name.
Subclasses should ensure that this gets called from overridden close()
methods.
Conditionally emits the specified logging record, depending on filters which may have been added to the handler. Wraps the actual emission of the record with acquisition/release of the I/O thread lock.
This method should be called from handlers when an exception is encountered
during an emit() call. If the module-level attribute
raiseExceptions is False, exceptions get silently ignored. This is
what is mostly wanted for a logging system - most users will not care about
errors in the logging system, they are more interested in application
errors. You could, however, replace this with a custom handler if you wish.
The specified record is the one which was being processed when the exception
occurred. (The default value of raiseExceptions is True, as that is
more useful during development).
Do formatting for a record - if a formatter is set, use it. Otherwise, use the default formatter for the module.
Do whatever it takes to actually log the specified logging record. This version
is intended to be implemented by subclasses and so raises a
NotImplementedError.
Warning
This method is called after a handler-level lock is acquired, which is released after this method returns. When you override this method, note that you should be careful when calling anything that invokes other parts of the logging API which might do locking, because that might result in a deadlock. Specifically:
Logging configuration APIs acquire the module-level lock, and then individual handler-level locks as those handlers are configured.
Many logging APIs lock the module-level lock. If such an API is called from this method, it could cause a deadlock if a configuration call is made on another thread, because that thread will try to acquire the module-level lock before the handler-level lock, whereas this thread tries to acquire the module-level lock after the handler-level lock (because in this method, the handler-level lock has already been acquired).
For a list of handlers included as standard, see logging.handlers.
Responsible for converting a LogRecord to an output string
to be interpreted by a human or external system.
fmt (str) – A format string in the given style for
the logged output as a whole.
The possible mapping keys are drawn from the LogRecord object’s
LogRecord attributes.
If not specified, '%(message)s' is used,
which is just the logged message.
datefmt (str) – A format string in the given style for
the date/time portion of the logged output.
If not specified, the default described in formatTime() is used.
style (str) – Can be one of '%', '{' or '$' and determines
how the format string will be merged with its data: using one of
printf-style String Formatting (%), str.format() ({)
or string.Template ($). This only applies to
fmt and datefmt (e.g. '%(message)s' versus '{message}'),
not to the actual log messages passed to the logging methods.
However, there are other ways
to use {- and $-formatting for log messages.
validate (bool) – If True (the default), incorrect or mismatched
fmt and style will raise a ValueError; for example,
logging.Formatter('%(asctime)s - %(message)s', style='{').
defaults (dict[str, Any]) – A dictionary with default values to use in custom fields.
For example,
logging.Formatter('%(ip)s %(message)s', defaults={"ip": None})
Changed in version 3.2: Added the style parameter.
Changed in version 3.8: Added the validate parameter.
Changed in version 3.10: Added the defaults parameter.
The record’s attribute dictionary is used as the operand to a string
formatting operation. Returns the resulting string. Before formatting the
dictionary, a couple of preparatory steps are carried out. The message
attribute of the record is computed using msg % args. If the
formatting string contains '(asctime)', formatTime() is called
to format the event time. If there is exception information, it is
formatted using formatException() and appended to the message. Note
that the formatted exception information is cached in attribute
exc_text. This is useful because the exception information can be
pickled and sent across the wire, but you should be careful if you have
more than one Formatter subclass which customizes the formatting
of exception information. In this case, you will have to clear the cached
value (by setting the exc_text attribute to None) after a formatter
has done its formatting, so that the next formatter to handle the event
doesn’t use the cached value, but recalculates it afresh.
If stack information is available, it’s appended after the exception
information, using formatStack() to transform it if necessary.
This method should be called from format() by a formatter which
wants to make use of a formatted time. This method can be overridden in
formatters to provide for any specific requirement, but the basic behavior
is as follows: if datefmt (a string) is specified, it is used with
time.strftime() to format the creation time of the
record. Otherwise, the format ‘%Y-%m-%d %H:%M:%S,uuu’ is used, where the
uuu part is a millisecond value and the other letters are as per the
time.strftime() documentation. An example time in this format is
2003-01-23 00:29:50,411. The resulting string is returned.
This function uses a user-configurable function to convert the creation
time to a tuple. By default, time.localtime() is used; to change
this for a particular formatter instance, set the converter attribute
to a function with the same signature as time.localtime() or
time.gmtime(). To change it for all formatters, for example if you
want all logging times to be shown in GMT, set the converter
attribute in the Formatter class.
Changed in version 3.3: Previously, the default format was hard-coded as in this example:
2010-09-06 22:38:15,292 where the part before the comma is
handled by a strptime format string ('%Y-%m-%d %H:%M:%S'), and the
part after the comma is a millisecond value. Because strptime does not
have a format placeholder for milliseconds, the millisecond value is
appended using another format string, '%s,%03d' — and both of these
format strings have been hardcoded into this method. With the change,
these strings are defined as class-level attributes which can be
overridden at the instance level when desired. The names of the
attributes are default_time_format (for the strptime format string)
and default_msec_format (for appending the millisecond value).
Changed in version 3.9: The default_msec_format can be None.
Formats the specified exception information (a standard exception tuple as
returned by sys.exc_info()) as a string. This default implementation
just uses traceback.print_exception(). The resulting string is
returned.
Formats the specified stack information (a string as returned by
traceback.print_stack(), but with the last newline removed) as a
string. This default implementation just returns the input value.
A base formatter class suitable for subclassing when you want to format a
number of records. You can pass a Formatter instance which you want
to use to format each line (that corresponds to a single record). If not
specified, the default formatter (which just outputs the event message) is
used as the line formatter.
Return a header for a list of records. The base implementation just returns the empty string. You will need to override this method if you want specific behaviour, e.g. to show the count of records, a title or a separator line.
Return a footer for a list of records. The base implementation just returns the empty string. You will need to override this method if you want specific behaviour, e.g. to show the count of records or a separator line.
Return formatted text for a list of records. The base implementation just returns the empty string if there are no records; otherwise, it returns the concatenation of the header, each record formatted with the line formatter, and the footer.
Filters can be used by Handlers and Loggers for more sophisticated
filtering than is provided by levels. The base filter class only allows events
which are below a certain point in the logger hierarchy. For example, a filter
initialized with ‘A.B’ will allow events logged by loggers ‘A.B’, ‘A.B.C’,
‘A.B.C.D’, ‘A.B.D’ etc. but not ‘A.BB’, ‘B.A.B’ etc. If initialized with the
empty string, all events are passed.
Returns an instance of the Filter class. If name is specified, it
names a logger which, together with its children, will have its events allowed
through the filter. If name is the empty string, allows every event.
Is the specified record to be logged? Returns false for no, true for yes. Filters can either modify log records in-place or return a completely different record instance which will replace the original log record in any future processing of the event.
Note that filters attached to handlers are consulted before an event is
emitted by the handler, whereas filters attached to loggers are consulted
whenever an event is logged (using debug(), info(),
etc.), before sending an event to handlers. This means that events which have
been generated by descendant loggers will not be filtered by a logger’s filter
setting, unless the filter has also been applied to those descendant loggers.
You don’t actually need to subclass Filter: you can pass any instance
which has a filter method with the same semantics.
Changed in version 3.2: You don’t need to create specialized Filter classes, or use other
classes with a filter method: you can use a function (or other
callable) as a filter. The filtering logic will check to see if the filter
object has a filter attribute: if it does, it’s assumed to be a
Filter and its filter() method is called. Otherwise, it’s
assumed to be a callable and called with the record as the single
parameter. The returned value should conform to that returned by
filter().
Changed in version 3.12: You can now return a LogRecord instance from filters to replace
the log record rather than modifying it in place. This allows filters attached to
a Handler to modify the log record before it is emitted, without
having side effects on other handlers.
Although filters are used primarily to filter records based on more
sophisticated criteria than levels, they get to see every record which is
processed by the handler or logger they’re attached to: this can be useful if
you want to do things like counting how many records were processed by a
particular logger or handler, or adding, changing or removing attributes in
the LogRecord being processed. Obviously changing the LogRecord needs
to be done with some care, but it does allow the injection of contextual
information into logs (see Using Filters to impart contextual information).
LogRecord instances are created automatically by the Logger
every time something is logged, and can be created manually via
makeLogRecord() (for example, from a pickled event received over the
wire).
Contains all the information pertinent to the event being logged.
The primary information is passed in msg and args,
which are combined using msg % args to create
the message attribute of the record.
name (str) – The name of the logger used to log the event
represented by this LogRecord.
Note that the logger name in the LogRecord
will always have this value,
even though it may be emitted by a handler
attached to a different (ancestor) logger.
level (int) – The numeric level of the logging event
(such as 10 for DEBUG, 20 for INFO, etc).
Note that this is converted to two attributes of the LogRecord:
levelno for the numeric value
and levelname for the corresponding level name.
pathname (str) – The full string path of the source file where the logging call was made.
lineno (int) – The line number in the source file where the logging call was made.
msg (Any) – The event description message, which can be a %-format string with placeholders for variable data, or an arbitrary object (see Using arbitrary objects as messages).
args (tuple | dict[str, Any]) – Variable data to merge into the msg argument to obtain the event description.
exc_info (tuple[type[BaseException], BaseException, types.TracebackType] | None) – An exception tuple with the current exception information,
as returned by sys.exc_info(),
or None if no exception information is available.
func (str | None) – The name of the function or method from which the logging call was invoked.
sinfo (str | None) – A text string representing stack information from the base of the stack in the current thread, up to the logging call.
Returns the message for this LogRecord instance after merging any
user-supplied arguments with the message. If the user-supplied message
argument to the logging call is not a string, str() is called on it to
convert it to a string. This allows use of user-defined classes as
messages, whose __str__ method can return the actual format string to
be used.
Changed in version 3.2: The creation of a LogRecord has been made more configurable by
providing a factory which is used to create the record. The factory can be
set using getLogRecordFactory() and setLogRecordFactory()
(see this for the factory’s signature).
This functionality can be used to inject your own values into a
LogRecord at creation time. You can use the following pattern:
old_factory = logging.getLogRecordFactory()
def record_factory(*args, **kwargs):
record = old_factory(*args, **kwargs)
record.custom_attribute = 0xdecafbad
return record
logging.setLogRecordFactory(record_factory)
With this pattern, multiple factories could be chained, and as long as they don’t overwrite each other’s attributes or unintentionally overwrite the standard attributes listed above, there should be no surprises.
The LogRecord has a number of attributes, most of which are derived from the parameters to the constructor. (Note that the names do not always correspond exactly between the LogRecord constructor parameters and the LogRecord attributes.) These attributes can be used to merge data from the record into the format string. The following table lists (in alphabetical order) the attribute names, their meanings and the corresponding placeholder in a %-style format string.
If you are using {}-formatting (str.format()), you can use
{attrname} as the placeholder in the format string. If you are using
$-formatting (string.Template), use the form ${attrname}. In
both cases, of course, replace attrname with the actual attribute name
you want to use.
In the case of {}-formatting, you can specify formatting flags by placing them
after the attribute name, separated from it with a colon. For example: a
placeholder of {msecs:03.0f} would format a millisecond value of 4 as
004. Refer to the str.format() documentation for full details on
the options available to you.
Attribute name |
Format |
Description |
|---|---|---|
args |
You shouldn’t need to format this yourself. |
The tuple of arguments merged into |
asctime |
|
Human-readable time when the
|
created |
|
Time when the |
exc_info |
You shouldn’t need to format this yourself. |
Exception tuple (à la |
filename |
|
Filename portion of |
funcName |
|
Name of function containing the logging call. |
levelname |
|
Text logging level for the message
( |
levelno |
|
Numeric logging level for the message
( |
lineno |
|
Source line number where the logging call was issued (if available). |
message |
|
The logged message, computed as |
module |
|
Module (name portion of |
msecs |
|
Millisecond portion of the time when the
|
msg |
You shouldn’t need to format this yourself. |
The format string passed in the original
logging call. Merged with |
name |
|
Name of the logger used to log the call. |
pathname |
|
Full pathname of the source file where the logging call was issued (if available). |
process |
|
Process ID (if available). |
processName |
|
Process name (if available). |
relativeCreated |
|
Time in milliseconds when the LogRecord was created, relative to the time the logging module was loaded. |
stack_info |
You shouldn’t need to format this yourself. |
Stack frame information (where available) from the bottom of the stack in the current thread, up to and including the stack frame of the logging call which resulted in the creation of this record. |
thread |
|
Thread ID (if available). |
threadName |
|
Thread name (if available). |
taskName |
|
|
Changed in version 3.1: processName was added.
Changed in version 3.12: taskName was added.
LoggerAdapter instances are used to conveniently pass contextual
information into logging calls. For a usage example, see the section on
adding contextual information to your logging output.
Returns an instance of LoggerAdapter initialized with an
underlying Logger instance, a dict-like object (extra), and a
boolean (merge_extra) indicating whether or not the extra argument of
individual log calls should be merged with the LoggerAdapter extra.
The default behavior is to ignore the extra argument of individual log
calls and only use the one of the LoggerAdapter instance
Modifies the message and/or keyword arguments passed to a logging call in order to insert contextual information. This implementation takes the object passed as extra to the constructor and adds it to kwargs using key ‘extra’. The return value is a (msg, kwargs) tuple which has the (possibly modified) versions of the arguments passed in.
Delegates to the underlying manager on logger.
Delegates to the underlying _log() method on logger.
In addition to the above, LoggerAdapter supports the following
methods of Logger: debug(), info(),
warning(), error(), exception(),
critical(), log(), isEnabledFor(),
getEffectiveLevel(), setLevel() and
hasHandlers(). These methods have the same signatures as their
counterparts in Logger, so you can use the two types of instances
interchangeably.
Changed in version 3.2: The isEnabledFor(), getEffectiveLevel(),
setLevel() and hasHandlers() methods were added
to LoggerAdapter. These methods delegate to the underlying logger.
Changed in version 3.6: Attribute manager and method _log() were added, which
delegate to the underlying logger and allow adapters to be nested.
Changed in version 3.13: The merge_extra argument was added.
The logging module is intended to be thread-safe without any special work needing to be done by its clients. It achieves this though using threading locks; there is one lock to serialize access to the module’s shared data, and each handler also creates a lock to serialize access to its underlying I/O.
If you are implementing asynchronous signal handlers using the signal
module, you may not be able to use logging from within such handlers. This is
because lock implementations in the threading module are not always
re-entrant, and so cannot be invoked from such signal handlers.
In addition to the classes described above, there are a number of module-level functions.
Return a logger with the specified name or, if name is None, return the
root logger of the hierarchy. If specified, the name is typically a
dot-separated hierarchical name like ‘a’, ‘a.b’ or ‘a.b.c.d’. Choice
of these names is entirely up to the developer who is using logging, though
it is recommended that __name__ be used unless you have a specific
reason for not doing that, as mentioned in Logger Objects.
All calls to this function with a given name return the same logger instance. This means that logger instances never need to be passed between different parts of an application.
Return either the standard Logger class, or the last class passed to
setLoggerClass(). This function may be called from within a new class
definition, to ensure that installing a customized Logger class will
not undo customizations already applied by other code. For example:
class MyLogger(logging.getLoggerClass()):
# ... override behaviour here
Return a callable which is used to create a LogRecord.
Added in version 3.2: This function has been provided, along with setLogRecordFactory(),
to allow developers more control over how the LogRecord
representing a logging event is constructed.
See setLogRecordFactory() for more information about the how the
factory is called.
This is a convenience function that calls Logger.debug(), on the root
logger. The handling of the arguments is in every way identical
to what is described in that method.
The only difference is that if the root logger has no handlers, then
basicConfig() is called, prior to calling debug on the root logger.
For very short scripts or quick demonstrations of logging facilities,
debug and the other module-level functions may be convenient. However,
most programs will want to carefully and explicitly control the logging
configuration, and should therefore prefer creating a module-level logger and
calling Logger.debug() (or other level-specific methods) on it, as
described at the beginnning of this documentation.
Logs a message with level INFO on the root logger. The arguments and behavior
are otherwise the same as for debug().
Logs a message with level WARNING on the root logger. The arguments and behavior
are otherwise the same as for debug().
Note
There is an obsolete function warn which is functionally
identical to warning. As warn is deprecated, please do not use
it - use warning instead.
Logs a message with level ERROR on the root logger. The arguments and behavior
are otherwise the same as for debug().
Logs a message with level CRITICAL on the root logger. The arguments and behavior
are otherwise the same as for debug().
Logs a message with level ERROR on the root logger. The arguments and behavior
are otherwise the same as for debug(). Exception info is added to the logging
message. This function should only be called from an exception handler.
Logs a message with level level on the root logger. The arguments and behavior
are otherwise the same as for debug().
Provides an overriding level level for all loggers which takes precedence over
the logger’s own level. When the need arises to temporarily throttle logging
output down across the whole application, this function can be useful. Its
effect is to disable all logging calls of severity level and below, so that
if you call it with a value of INFO, then all INFO and DEBUG events would be
discarded, whereas those of severity WARNING and above would be processed
according to the logger’s effective level. If
logging.disable(logging.NOTSET) is called, it effectively removes this
overriding level, so that logging output again depends on the effective
levels of individual loggers.
Note that if you have defined any custom logging level higher than
CRITICAL (this is not recommended), you won’t be able to rely on the
default value for the level parameter, but will have to explicitly supply a
suitable value.
Changed in version 3.7: The level parameter was defaulted to level CRITICAL. See
bpo-28524 for more information about this change.
Associates level level with text levelName in an internal dictionary, which is
used to map numeric levels to a textual representation, for example when a
Formatter formats a message. This function can also be used to define
your own levels. The only constraints are that all levels used must be
registered using this function, levels should be positive integers and they
should increase in increasing order of severity.
Note
If you are thinking of defining your own levels, please see the section on Custom Levels.
Returns a mapping from level names to their corresponding logging levels. For example, the
string “CRITICAL” maps to CRITICAL. The returned mapping is copied from an internal
mapping on each call to this function.
Added in version 3.11.
Returns the textual or numeric representation of logging level level.
If level is one of the predefined levels CRITICAL, ERROR,
WARNING, INFO or DEBUG then you get the
corresponding string. If you have associated levels with names using
addLevelName() then the name you have associated with level is
returned. If a numeric value corresponding to one of the defined levels is
passed in, the corresponding string representation is returned.
The level parameter also accepts a string representation of the level such as ‘INFO’. In such cases, this functions returns the corresponding numeric value of the level.
If no matching numeric or string value is passed in, the string ‘Level %s’ % level is returned.
Note
Levels are internally integers (as they need to be compared in the
logging logic). This function is used to convert between an integer level
and the level name displayed in the formatted log output by means of the
%(levelname)s format specifier (see LogRecord attributes), and
vice versa.
Changed in version 3.4: In Python versions earlier than 3.4, this function could also be passed a text level, and would return the corresponding numeric value of the level. This undocumented behaviour was considered a mistake, and was removed in Python 3.4, but reinstated in 3.4.2 due to retain backward compatibility.
Returns a handler with the specified name, or None if there is no handler
with that name.
Added in version 3.12.
Returns an immutable set of all known handler names.
Added in version 3.12.
Creates and returns a new LogRecord instance whose attributes are
defined by attrdict. This function is useful for taking a pickled
LogRecord attribute dictionary, sent over a socket, and reconstituting
it as a LogRecord instance at the receiving end.
Does basic configuration for the logging system by creating a
StreamHandler with a default Formatter and adding it to the
root logger. The functions debug(), info(), warning(),
error() and critical() will call basicConfig() automatically
if no handlers are defined for the root logger.
This function does nothing if the root logger already has handlers
configured, unless the keyword argument force is set to True.
Note
This function should be called from the main thread before other threads are started. In versions of Python prior to 2.7.1 and 3.2, if this function is called from multiple threads, it is possible (in rare circumstances) that a handler will be added to the root logger more than once, leading to unexpected results such as messages being duplicated in the log.
The following keyword arguments are supported.
Format |
Description |
|---|---|
filename |
Specifies that a |
filemode |
If filename is specified, open the file
in this mode. Defaults
to |
format |
Use the specified format string for the
handler. Defaults to attributes
|
datefmt |
Use the specified date/time format, as
accepted by |
style |
If format is specified, use this style
for the format string. One of |
level |
Set the root logger level to the specified level. |
stream |
Use the specified stream to initialize the
|
handlers |
If specified, this should be an iterable of
already created handlers to add to the root
logger. Any handlers which don’t already
have a formatter set will be assigned the
default formatter created in this function.
Note that this argument is incompatible
with filename or stream - if both
are present, a |
force |
If this keyword argument is specified as true, any existing handlers attached to the root logger are removed and closed, before carrying out the configuration as specified by the other arguments. |
encoding |
If this keyword argument is specified along
with filename, its value is used when the
|
errors |
If this keyword argument is specified along
with filename, its value is used when the
|
Changed in version 3.2: The style argument was added.
Changed in version 3.3: The handlers argument was added. Additional checks were added to catch situations where incompatible arguments are specified (e.g. handlers together with stream or filename, or stream together with filename).
Changed in version 3.8: The force argument was added.
Changed in version 3.9: The encoding and errors arguments were added.
Informs the logging system to perform an orderly shutdown by flushing and closing all handlers. This should be called at application exit and no further use of the logging system should be made after this call.
When the logging module is imported, it registers this function as an exit
handler (see atexit), so normally there’s no need to do that
manually.
Tells the logging system to use the class klass when instantiating a logger.
The class should define __init__() such that only a name argument is
required, and the __init__() should call Logger.__init__(). This
function is typically called before any loggers are instantiated by applications
which need to use custom logger behavior. After this call, as at any other
time, do not instantiate loggers directly using the subclass: continue to use
the logging.getLogger() API to get your loggers.
Set a callable which is used to create a LogRecord.
factory – The factory callable to be used to instantiate a log record.
Added in version 3.2: This function has been provided, along with getLogRecordFactory(), to
allow developers more control over how the LogRecord representing
a logging event is constructed.
The factory has the following signature:
factory(name, level, fn, lno, msg, args, exc_info, func=None, sinfo=None, **kwargs)
- name:
The logger name.
- level:
The logging level (numeric).
- fn:
The full pathname of the file where the logging call was made.
- lno:
The line number in the file where the logging call was made.
- msg:
The logging message.
- args:
The arguments for the logging message.
- exc_info:
An exception tuple, or
None.- func:
The name of the function or method which invoked the logging call.
- sinfo:
A stack traceback such as is provided by
traceback.print_stack(), showing the call hierarchy.- kwargs:
Additional keyword arguments.
A “handler of last resort” is available through this attribute. This
is a StreamHandler writing to sys.stderr with a level of
WARNING, and is used to handle logging events in the absence of any
logging configuration. The end result is to just print the message to
sys.stderr. This replaces the earlier error message saying that
“no handlers could be found for logger XYZ”. If you need the earlier
behaviour for some reason, lastResort can be set to None.
Added in version 3.2.
Used to see if exceptions during handling should be propagated.
Default: True.
If raiseExceptions is False,
exceptions get silently ignored. This is what is mostly wanted
for a logging system - most users will not care about errors in
the logging system, they are more interested in application errors.
The captureWarnings() function can be used to integrate logging
with the warnings module.
This function is used to turn the capture of warnings by logging on and off.
If capture is True, warnings issued by the warnings module will
be redirected to the logging system. Specifically, a warning will be
formatted using warnings.formatwarning() and the resulting string
logged to a logger named 'py.warnings' with a severity of WARNING.
If capture is False, the redirection of warnings to the logging system
will stop, and warnings will be redirected to their original destinations
(i.e. those in effect before captureWarnings(True) was called).
See also
logging.configConfiguration API for the logging module.
logging.handlersUseful handlers included with the logging module.
The proposal which described this feature for inclusion in the Python standard library.
This is the original source for the logging package. The version of the
package available from this site is suitable for use with Python 1.5.2, 2.1.x
and 2.2.x, which do not include the logging package in the standard
library.