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Diffstat (limited to 'Doc/lib/liblogging.tex')
| -rw-r--r-- | Doc/lib/liblogging.tex | 170 |
1 files changed, 118 insertions, 52 deletions
diff --git a/Doc/lib/liblogging.tex b/Doc/lib/liblogging.tex index c86596d..2e8e16e 100644 --- a/Doc/lib/liblogging.tex +++ b/Doc/lib/liblogging.tex @@ -200,8 +200,9 @@ level is one of the predefined levels \constant{CRITICAL}, \constant{ERROR}, \constant{WARNING}, \constant{INFO} or \constant{DEBUG} then you get the corresponding string. If you have associated levels with names using \function{addLevelName()} then the name you have associated -with \var{lvl} is returned. Otherwise, the string "Level \%s" \% lvl is -returned. +with \var{lvl} is returned. If a numeric value corresponding to one of the +defined levels is passed in, the corresponding string representation is +returned. Otherwise, the string "Level \%s" \% lvl is returned. \end{funcdesc} \begin{funcdesc}{makeLogRecord}{attrdict} @@ -243,8 +244,8 @@ behavior. {Original Python \module{logging} package} {This is the original source for the \module{logging} package. The version of the package available from this - site is suitable for use with Python 2.1.x and 2.2.x, which - do not include the \module{logging} package in the standard + site is suitable for use with Python 1.5.2, 2.1.x and 2.2.x, + which do not include the \module{logging} package in the standard library.} \end{seealso} @@ -363,6 +364,112 @@ This is a factory method which can be overridden in subclasses to create specialized \class{LogRecord} instances. \end{methoddesc} +\subsection{Basic example \label{minimal-example}} + +The \module{logging} package provides a lot of flexibility, and its +configuration can appear daunting. This section demonstrates that simple +use of the logging package is possible. + +The simplest example shows logging to the console: + +\begin{verbatim} +import logging + +logging.debug('A debug message') +logging.info('Some information') +logging.warning('A shot across the bows') +\end{verbatim} + +If you run the above script, you'll see this: +\begin{verbatim} +WARNING:root:A shot across the bows +\end{verbatim} + +Because no particular logger was specified, the system used the root logger. +The debug and info messages didn't appear because by default, the root +logger is configured to only handle messages with a severity of WARNING +or above. The message format is also a configuration default, as is the output +destination of the messages - \code{sys.stderr}. The severity level, +the message format and destination can be easily changed, as shown in +the example below: + +\begin{verbatim} +import logging + +logging.basicConfig(level=logging.DEBUG, + format='%(asctime)s %(levelname)s %(message)s', + filename='/tmp/myapp.log', + filemode='w') +logging.debug('A debug message') +logging.info('Some information') +logging.warning('A shot across the bows') +\end{verbatim} + +The \method{basicConfig()} method is used to change the configuration +defaults, which results in output (written to \code{/tmp/myapp.log}) +which should look something like the following: + +\begin{verbatim} +2004-07-02 13:00:08,743 DEBUG A debug message +2004-07-02 13:00:08,743 INFO Some information +2004-07-02 13:00:08,743 WARNING A shot across the bows +\end{verbatim} + +This time, all messages with a severity of DEBUG or above were handled, +and the format of the messages was also changed, and output went to the +specified file rather than the console. + +Formatting uses standard Python string formatting - see section +\ref{typesseq-strings}. The format string takes the following +common specifiers. For a complete list of specifiers, consult the +\class{Formatter} documentation. + +\begin{tableii}{l|l}{code}{Format}{Description} +\lineii{\%(name)s} {Name of the logger (logging channel).} +\lineii{\%(levelname)s}{Text logging level for the message + (\code{'DEBUG'}, \code{'INFO'}, + \code{'WARNING'}, \code{'ERROR'}, + \code{'CRITICAL'}).} +\lineii{\%(asctime)s} {Human-readable time when the \class{LogRecord} + was created. By default this is of the form + ``2003-07-08 16:49:45,896'' (the numbers after the + comma are millisecond portion of the time).} +\lineii{\%(message)s} {The logged message.} +\end{tableii} + +To change the date/time format, you can pass an additional keyword parameter, +\var{datefmt}, as in the following: + +\begin{verbatim} +import logging + +logging.basicConfig(level=logging.DEBUG, + format='%(asctime)s %(levelname)-8s %(message)s', + datefmt='%a, %d %b %Y %H:%M:%S', + filename='/temp/myapp.log', + filemode='w') +logging.debug('A debug message') +logging.info('Some information') +logging.warning('A shot across the bows') +\end{verbatim} + +which would result in output like + +\begin{verbatim} +Fri, 02 Jul 2004 13:06:18 DEBUG A debug message +Fri, 02 Jul 2004 13:06:18 INFO Some information +Fri, 02 Jul 2004 13:06:18 WARNING A shot across the bows +\end{verbatim} + +The date format string follows the requirements of \function{strftime()} - +see the documentation for the \refmodule{time} module. + +If, instead of sending logging output to the console or a file, you'd rather +use a file-like object which you have created separately, you can pass it +to \function{basicConfig()} using the \var{stream} keyword argument. Note +that if both \var{stream} and \var{filename} keyword arguments are passed, +the \var{stream} argument is ignored. + \subsection{Handler Objects} Handlers have the following attributes and methods. Note that @@ -429,14 +536,15 @@ emission of the record with acquisition/release of the I/O thread lock. \end{methoddesc} -\begin{methoddesc}{handleError}{} +\begin{methoddesc}{handleError}{record} This method should be called from handlers when an exception is -encountered during an emit() call. By default it does nothing, +encountered during an \method{emit()} call. By default it does nothing, which means that 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. +handler if you wish. The specified record is the one which was being +processed when the exception occurred. \end{methoddesc} \begin{methoddesc}{format}{record} @@ -506,7 +614,7 @@ The \class{RotatingFileHandler} class supports rotation of disk log files. Returns a new instance of the \class{RotatingFileHandler} class. The specified file is opened and used as the stream for logging. If \var{mode} is not specified, \code{'a'} is used. By default, the -file grows indefinitely. +file grows indefinitely. You can use the \var{maxBytes} and \var{backupCount} values to allow the file to \dfn{rollover} at a @@ -522,7 +630,7 @@ a \var{backupCount} of 5 and a base file name of written to is always \file{app.log}. When this file is filled, it is closed and renamed to \file{app.log.1}, and if files \file{app.log.1}, \file{app.log.2}, etc. exist, then they are renamed to \file{app.log.2}, -\file{app.log.3} etc. respectively. +\file{app.log.3} etc. respectively. \end{classdesc} \begin{methoddesc}{doRollover}{} @@ -1051,7 +1159,7 @@ entry is set to 1 to indicate that messages must propagate to handlers higher up the logger hierarchy from this logger, or 0 to indicate that messages are \strong{not} propagated to handlers up the hierarchy. The \code{qualname} entry is the hierarchical channel name of the logger, -for example, the name used by the application to get the logger. +that is to say the name used by the application to get the logger. Sections which specify handler configuration are exemplified by the following. @@ -1147,45 +1255,3 @@ is almost equivalent to specifying the date format string "%Y-%m-%d %H:%M:%S". The ISO8601 format also specifies milliseconds, which are appended to the result of using the above format string, with a comma separator. An example time in ISO8601 format is \code{2003-01-23 00:29:50,411}. - -\subsection{Using the logging package} - -\subsubsection{Basic example - log to a file} - -Here's a simple logging example that just logs to a file. In order, -it creates a \class{Logger} instance, then a \class{FileHandler} -and a \class{Formatter}. It attaches the \class{Formatter} to the -\class{FileHandler}, then the \class{FileHandler} to the \class{Logger}. -Finally, it sets a debug level for the logger. - -\begin{verbatim} -import logging -logger = logging.getLogger('myapp') -hdlr = logging.FileHandler('/var/tmp/myapp.log') -formatter = logging.Formatter('%(asctime)s %(levelname)s %(message)s') -hdlr.setFormatter(formatter) -logger.addHandler(hdlr) -logger.setLevel(logging.WARNING) -\end{verbatim} - -We can use this logger object now to write entries to the log file: - -\begin{verbatim} -logger.error('We have a problem') -logger.info('While this is just chatty') -\end{verbatim} - -If we look in the file that was created, we'll see something like this: -\begin{verbatim} -2003-07-08 16:49:45,896 ERROR We have a problem -\end{verbatim} - -The info message was not written to the file: we called the -\method{setLevel()} method to say we only wanted \constant{WARNING} or -worse, so the info message is discarded. - -The timestamp is of the form -``year-month-day hour:minutes:seconds,milliseconds.'' -Note that despite the three digits of precision in the milliseconds field, -not all systems provide time with this much precision. - |