Commit b322621a authored by Vinay Sajip's avatar Vinay Sajip

Added clarification to logging HOWTO.

parent 64cca126
...@@ -738,12 +738,11 @@ Configuring Logging for a Library ...@@ -738,12 +738,11 @@ Configuring Logging for a Library
When developing a library which uses logging, you should take care to When developing a library which uses logging, you should take care to
document how the library uses logging - for example, the names of loggers document how the library uses logging - for example, the names of loggers
used. Some consideration also needs to be given to its logging configuration. used. Some consideration also needs to be given to its logging configuration.
If the using application does not use logging, and library code makes logging If the using application does not configure logging, and library code makes
calls, then (as described in the previous section) events of severity logging calls, then (as described in the previous section) an error message
``WARNING`` and greater will be printed to ``sys.stderr``. This is regarded as will be printed to ``sys.stderr``.
the best default behaviour.
If for some reason you *don't* want these messages printed in the absence of If for some reason you *don't* want this message printed in the absence of
any logging configuration, you can attach a do-nothing handler to the top-level any logging configuration, you can attach a do-nothing handler to the top-level
logger for your library. This avoids the message being printed, since a handler logger for your library. This avoids the message being printed, since a handler
will be always be found for the library's events: it just doesn't produce any will be always be found for the library's events: it just doesn't produce any
...@@ -755,7 +754,7 @@ handlers, as normal. ...@@ -755,7 +754,7 @@ handlers, as normal.
A do-nothing handler is included in the logging package: A do-nothing handler is included in the logging package:
:class:`~logging.NullHandler` (since Python 2.7). An instance of this handler :class:`~logging.NullHandler` (since Python 2.7). An instance of this handler
could be added to the top-level logger of the logging namespace used by the could be added to the top-level logger of the logging namespace used by the
library (*if* you want to prevent your library's logged events being output to library (*if* you want to prevent an error message being output to
``sys.stderr`` in the absence of logging configuration). If all logging by a ``sys.stderr`` in the absence of logging configuration). If all logging by a
library *foo* is done using loggers with names matching 'foo.x', 'foo.x.y', library *foo* is done using loggers with names matching 'foo.x', 'foo.x.y',
etc. then the code:: etc. then the code::
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