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authorVinay Sajip <vinay_sajip@yahoo.co.uk>2010-09-17 10:09:04 (GMT)
committerVinay Sajip <vinay_sajip@yahoo.co.uk>2010-09-17 10:09:04 (GMT)
commitc8c8c6968b076b61bd6873e1f92f8b918387ee6c (patch)
tree9f5547cc522ca0e4f19944c09f23aaf8b28479b3 /Doc
parentfc2e1d10bc343d971a43faacffd5d69a39c3fa8e (diff)
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Improved basicConfig and custom level documentation.
Diffstat (limited to 'Doc')
-rw-r--r--Doc/library/logging.rst35
1 files changed, 33 insertions, 2 deletions
diff --git a/Doc/library/logging.rst b/Doc/library/logging.rst
index a05b99f..d9fcb23 100644
--- a/Doc/library/logging.rst
+++ b/Doc/library/logging.rst
@@ -589,6 +589,22 @@ decides to actually dispatch an event, the :meth:`emit` method is used to send
the message to its destination. Most user-defined subclasses of :class:`Handler`
will need to override this :meth:`emit`.
+.. _custom-levels:
+
+Custom Levels
+^^^^^^^^^^^^^
+
+Defining your own levels is possible, but should not be necessary, as the
+existing levels have been chosen on the basis of practical experience.
+However, if you are convinced that you need custom levels, great care should
+be exercised when doing this, and it is possibly *a very bad idea to define
+custom levels if you are developing a library*. That's because if multiple
+library authors all define their own custom levels, there is a chance that
+the logging output from such multiple libraries used together will be
+difficult for the using developer to control and/or interpret, because a
+given numeric value might mean different things for different libraries.
+
+
Useful Handlers
---------------
@@ -790,12 +806,19 @@ functions.
interpreted as for :func:`debug`. Exception info is added to the logging
message. This function should only be called from an exception handler.
-
.. function:: log(level, msg, *args, **kwargs)
Logs a message with level *level* on the root logger. The other arguments are
interpreted as for :func:`debug`.
+ PLEASE NOTE: The above module-level functions which delegate to the root
+ logger should *not* be used in threads, in versions of Python earlier than
+ 2.7.1 and 3.2, unless at least one handler has been added to the root
+ logger *before* the threads are started. These convenience functions call
+ :func:`basicConfig` to ensure that at least one handler is available; in
+ earlier versions of Python, this can (under rare circumstances) lead to
+ handlers being added multiple times to the root logger, which can in turn
+ lead to multiple messages for the same event.
.. function:: disable(lvl)
@@ -817,6 +840,8 @@ functions.
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 :ref:`custom-levels`.
.. function:: getLevelName(lvl)
@@ -848,6 +873,13 @@ functions.
This function does nothing if the root logger already has handlers
configured for it.
+ PLEASE 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.
+--------------+---------------------------------------------+
@@ -875,7 +907,6 @@ functions.
| | present, 'stream' is ignored. |
+--------------+---------------------------------------------+
-
.. function:: shutdown()
Informs the logging system to perform an orderly shutdown by flushing and