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Moved example section up to just after the section on Logger objects, and changed it to use the new basicConfig() API

This commit is contained in:
Vinay Sajip 2004-07-03 11:45:53 +00:00
parent d9c0a7ae94
commit a13c60b810
1 changed files with 118 additions and 52 deletions
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Doc/lib/liblogging.tex
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@ -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.