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# -*- test-case-name: twisted.logger.test.test_buffer -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Log observer that maintains a buffer.
"""
from collections import deque
from typing import Deque, Optional
from zope.interface import implementer
from ._interfaces import ILogObserver, LogEvent
_DEFAULT_BUFFER_MAXIMUM = 64 * 1024
@implementer(ILogObserver)
class LimitedHistoryLogObserver:
"""
L{ILogObserver} that stores events in a buffer of a fixed size::
>>> from twisted.logger import LimitedHistoryLogObserver
>>> history = LimitedHistoryLogObserver(5)
>>> for n in range(10): history({'n': n})
...
>>> repeats = []
>>> history.replayTo(repeats.append)
>>> len(repeats)
5
>>> repeats
[{'n': 5}, {'n': 6}, {'n': 7}, {'n': 8}, {'n': 9}]
>>>
"""
def __init__(self, size: Optional[int] = _DEFAULT_BUFFER_MAXIMUM) -> None:
"""
@param size: The maximum number of events to buffer. If L{None}, the
buffer is unbounded.
"""
self._buffer: Deque[LogEvent] = deque(maxlen=size)
def __call__(self, event: LogEvent) -> None:
self._buffer.append(event)
def replayTo(self, otherObserver: ILogObserver) -> None:
"""
Re-play the buffered events to another log observer.
@param otherObserver: An observer to replay events to.
"""
for event in self._buffer:
otherObserver(event)
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