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import logging
class QueueHandler(logging.Handler):
"""
This handler sends events to a queue. Typically, it would be used together
with a multiprocessing Queue to centralise logging to file in one process
(in a multi-process application), so as to avoid file write contention
between processes.
This code is new in Python 3.2, but this class can be copy pasted into
user code for use with earlier Python versions.
"""
def __init__(self, queue):
"""
Initialise an instance, using the passed queue.
"""
logging.Handler.__init__(self)
self.queue = queue
def enqueue(self, record):
"""
Enqueue a record.
The base implementation uses put_nowait. You may want to override
this method if you want to use blocking, timeouts or custom queue
implementations.
"""
self.queue.put_nowait(record)
def prepare(self, record):
"""
Prepares a record for queueing. The object returned by this
method is enqueued.
The base implementation formats the record to merge the message
and arguments, and removes unpickleable items from the record
in-place.
You might want to override this method if you want to convert
the record to a dict or JSON string, or send a modified copy
of the record while leaving the original intact.
"""
# The format operation gets traceback text into record.exc_text
# (if there's exception data), and also puts the message into
# record.message. We can then use this to replace the original
# msg + args, as these might be unpickleable. We also zap the
# exc_info attribute, as it's no longer needed and, if not None,
# will typically not be pickleable.
self.format(record)
record.msg = record.message
record.args = None
record.exc_info = None
return record
def emit(self, record):
"""
Emit a record.
Writes the LogRecord to the queue, preparing it first.
"""
try:
self.enqueue(self.prepare(record))
except (KeyboardInterrupt, SystemExit):
raise
except:
self.handleError(record)
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