liblogging.tex

xen虚拟机源代码安装包

\section{\module{logging} ---
         Logging facility for Python}

\declaremodule{standard}{logging}

% These apply to all modules, and may be given more than once:

\moduleauthor{Vinay Sajip}{[e-mail]}
\sectionauthor{Vinay Sajip}{[e-mail]}

\modulesynopsis{Logging module for Python based on \pep{282}.}

\indexii{Errors}{logging}

\versionadded{2.3}
This module defines functions and classes which implement a flexible
error logging system for applications.

Logging is performed by calling methods on instances of the
\class{Logger} class (hereafter called \dfn{loggers}). Each instance has a
name, and they are conceptually arranged in a name space hierarchy
using dots (periods) as separators. For example, a logger named
"scan" is the parent of loggers "scan.text", "scan.html" and "scan.pdf".
Logger names can be anything you want, and indicate the area of an
application in which a logged message originates.

Logged messages also have levels of importance associated with them.
The default levels provided are \constant{DEBUG}, \constant{INFO},
\constant{WARNING}, \constant{ERROR} and \constant{CRITICAL}. As a
convenience, you indicate the importance of a logged message by calling
an appropriate method of \class{Logger}. The methods are
\method{debug()}, \method{info()}, \method{warning()}, \method{error()} and
\method{critical()}, which mirror the default levels. You are not
constrained to use these levels: you can specify your own and use a
more general \class{Logger} method, \method{log()}, which takes an
explicit level argument.

Levels can also be associated with loggers, being set either by the
developer or through loading a saved logging configuration. When a
logging method is called on a logger, the logger compares its own
level with the level associated with the method call. If the logger's
level is higher than the method call's, no logging message is actually
generated. This is the basic mechanism controlling the verbosity of
logging output.

Logging messages are encoded as instances of the \class{LogRecord} class.
When a logger decides to actually log an event, an \class{LogRecord}
instance is created from the logging message.

Logging messages are subjected to a dispatch mechanism through the
use of \dfn{handlers}, which are instances of subclasses of the
\class{Handler} class. Handlers are responsible for ensuring that a logged
message (in the form of a \class{LogRecord}) ends up in a particular
location (or set of locations) which is useful for the target audience for
that message (such as end users, support desk staff, system administrators,
developers). Handlers are passed \class{LogRecord} instances intended for
particular destinations. Each logger can have zero, one or more handlers
associated with it (via the \method{addHandler} method of \class{Logger}).
In addition to any handlers directly associated with a logger,
\emph{all handlers associated with all ancestors of the logger} are
called to dispatch the message.

Just as for loggers, handlers can have levels associated with them.
A handler's level acts as a filter in the same way as a logger's level does.
If a handler decides to actually dispatch an event, the \method{emit()} method
is used to send the message to its destination. Most user-defined subclasses
of \class{Handler} will need to override this \method{emit()}.

In addition to the base \class{Handler} class, many useful subclasses
are provided:

\begin{enumerate}

\item \class{StreamHandler} instances send error messages to
streams (file-like objects).

\item \class{FileHandler} instances send error messages to disk
files.

\item \class{RotatingFileHandler} instances send error messages to disk
files, with support for maximum log file sizes and log file rotation.

\item \class{SocketHandler} instances send error messages to
TCP/IP sockets.

\item \class{DatagramHandler} instances send error messages to UDP
sockets.

\item \class{SMTPHandler} instances send error messages to a
designated email address.

\item \class{SysLogHandler} instances send error messages to a
\UNIX{} syslog daemon, possibly on a remote machine.

\item \class{NTEventLogHandler} instances send error messages to a
Windows NT/2000/XP event log.

\item \class{MemoryHandler} instances send error messages to a
buffer in memory, which is flushed whenever specific criteria are
met.

\item \class{HTTPHandler} instances send error messages to an
HTTP server using either \samp{GET} or \samp{POST} semantics.

\end{enumerate}

The \class{StreamHandler} and \class{FileHandler} classes are defined
in the core logging package. The other handlers are defined in a sub-
module, \module{logging.handlers}. (There is also another sub-module,
\module{logging.config}, for configuration functionality.)

Logged messages are formatted for presentation through instances of the
\class{Formatter} class. They are initialized with a format string
suitable for use with the \% operator and a dictionary.

For formatting multiple messages in a batch, instances of
\class{BufferingFormatter} can be used. In addition to the format string
(which is applied to each message in the batch), there is provision for
header and trailer format strings.

When filtering based on logger level and/or handler level is not enough,
instances of \class{Filter} can be added to both \class{Logger} and
\class{Handler} instances (through their \method{addFilter()} method).
Before deciding to process a message further, both loggers and handlers
consult all their filters for permission. If any filter returns a false
value, the message is not processed further.

The basic \class{Filter} functionality allows filtering by specific logger
name. If this feature is used, messages sent to the named logger and its
children are allowed through the filter, and all others dropped.

In addition to the classes described above, there are a number of module-
level functions.

\begin{funcdesc}{getLogger}{\optional{name}}
Return a logger with the specified name or, if no name is specified, return
a logger which is the root logger of the hierarchy.

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.
\end{funcdesc}

\begin{funcdesc}{debug}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{DEBUG} on the root logger.
The \var{msg} is the message format string, and the \var{args} are the
arguments which are merged into \var{msg}. The only keyword argument in
\var{kwargs} which is inspected is \var{exc_info} which, if it does not
evaluate as false, causes exception information (via a call to
\function{sys.exc_info()}) to be added to the logging message.
\end{funcdesc}

\begin{funcdesc}{info}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{INFO} on the root logger.
The arguments are interpreted as for \function{debug()}.
\end{funcdesc}

\begin{funcdesc}{warning}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{WARNING} on the root logger.
The arguments are interpreted as for \function{debug()}.
\end{funcdesc}

\begin{funcdesc}{error}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{ERROR} on the root logger.
The arguments are interpreted as for \function{debug()}.
\end{funcdesc}

\begin{funcdesc}{critical}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{CRITICAL} on the root logger.
The arguments are interpreted as for \function{debug()}.
\end{funcdesc}

\begin{funcdesc}{exception}{msg\optional{, *args}}
Logs a message with level \constant{ERROR} on the root logger.
The arguments are interpreted as for \function{debug()}. Exception info
is added to the logging message. This function should only be called
from an exception handler.
\end{funcdesc}

\begin{funcdesc}{disable}{lvl}
Provides an overriding level \var{lvl} 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.
\end{funcdesc}

\begin{funcdesc}{addLevelName}{lvl, levelName}
Associates level \var{lvl} with text \var{levelName} in an internal
dictionary, which is used to map numeric levels to a textual
representation, for example when a \class{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.
\end{funcdesc}

\begin{funcdesc}{getLevelName}{lvl}
Returns the textual representation of logging level \var{lvl}. If the
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.
\end{funcdesc}

\begin{funcdesc}{makeLogRecord}{attrdict}
Creates and returns a new \class{LogRecord} instance whose attributes are
defined by \var{attrdict}. This function is useful for taking a pickled
\class{LogRecord} attribute dictionary, sent over a socket, and reconstituting
it as a \class{LogRecord} instance at the receiving end.
\end{funcdesc}

\begin{funcdesc}{basicConfig}{}
Does basic configuration for the logging system by creating a
\class{StreamHandler} with a default \class{Formatter} and adding it to
the root logger. The functions \function{debug()}, \function{info()},
\function{warning()}, \function{error()} and \function{critical()} will call
\function{basicConfig()} automatically if no handlers are defined for the
root logger.
\end{funcdesc}

\begin{funcdesc}{shutdown}{}
Informs the logging system to perform an orderly shutdown by flushing and
closing all handlers.
\end{funcdesc}

\begin{funcdesc}{setLoggerClass}{klass}
Tells the logging system to use the class \var{klass} when instantiating a
logger. The class should define \method{__init__()} such that only a name
argument is required, and the \method{__init__()} should call
\method{Logger.__init__()}. This function is typically called before any
loggers are instantiated by applications which need to use custom logger
behavior.
\end{funcdesc}


\begin{seealso}
  \seepep{282}{A Logging System}
         {The proposal which described this feature for inclusion in
          the Python standard library.}
  \seelink{http://www.red-dove.com/python_logging.html}
          {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 1.5.2, 2.1.x and 2.2.x, which
           do not include the \module{logging} package in the standard
           library.}
\end{seealso}


\subsection{Logger Objects}

Loggers have the following attributes and methods. Note that Loggers are
never instantiated directly, but always through the module-level function
\function{logging.getLogger(name)}.

\begin{datadesc}{propagate}
If this evaluates to false, logging messages are not passed by this
logger or by child loggers to higher level (ancestor) loggers. The
constructor sets this attribute to 1.
\end{datadesc}

\begin{methoddesc}{setLevel}{lvl}
Sets the threshold for this logger to \var{lvl}. Logging messages
which are less severe than \var{lvl} will be ignored. When a logger is
created, the level is set to \constant{NOTSET} (which causes all messages
to be processed in the root logger, or delegation to the parent in non-root
loggers).
\end{methoddesc}

\begin{methoddesc}{isEnabledFor}{lvl}
Indicates if a message of severity \var{lvl} would be processed by
this logger.  This method checks first the module-level level set by
\function{logging.disable(lvl)} and then the logger's effective level as
determined by \method{getEffectiveLevel()}.
\end{methoddesc}

\begin{methoddesc}{getEffectiveLevel}{}
Indicates the effective level for this logger. If a value other than
\constant{NOTSET} has been set using \method{setLevel()}, it is returned.
Otherwise, the hierarchy is traversed towards the root until a value
other than \constant{NOTSET} is found, and that value is returned.
\end{methoddesc}

\begin{methoddesc}{debug}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{DEBUG} on this logger.
The \var{msg} is the message format string, and the \var{args} are the
arguments which are merged into \var{msg}. The only keyword argument in
\var{kwargs} which is inspected is \var{exc_info} which, if it does not
evaluate as false, causes exception information (via a call to
\function{sys.exc_info()}) to be added to the logging message.
\end{methoddesc}

\begin{methoddesc}{info}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{INFO} on this logger.
The arguments are interpreted as for \method{debug()}.
\end{methoddesc}

\begin{methoddesc}{warning}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{WARNING} on this logger.
The arguments are interpreted as for \method{debug()}.
\end{methoddesc}

\begin{methoddesc}{error}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{ERROR} on this logger.
The arguments are interpreted as for \method{debug()}.
\end{methoddesc}

\begin{methoddesc}{critical}{msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \constant{CRITICAL} on this logger.
The arguments are interpreted as for \method{debug()}.
\end{methoddesc}

\begin{methoddesc}{log}{lvl, msg\optional{, *args\optional{, **kwargs}}}
Logs a message with level \var{lvl} on this logger.
The other arguments are interpreted as for \method{debug()}.
\end{methoddesc}

\begin{methoddesc}{exception}{msg\optional{, *args}}
Logs a message with level \constant{ERROR} on this logger.