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详解Python logging调用Logger.info方法的处理过程

时间:2021-05-27 00:26     来源/作者:posuoren

本次分析一下logger.info的流程

1. logger.info源码:

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def info(self, msg, *args, **kwargs):
 """
 log 'msg % args' with severity 'info'.
 
 to pass exception information, use the keyword argument exc_info with
 a true value, e.g.
 
 logger.info("houston, we have a %s", "interesting problem", exc_info=1)
 """
 if self.isenabledfor(info):
  self._log(info, msg, args, **kwargs)

注释中反应了可以通过 msg和不定参数args来进行日志的格式化。
真实的调用为:_log方法:

2. logger._log方法:

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def _log(self, level, msg, args, exc_info=none, extra=none, stack_info=false):
 """
 low-level logging routine which creates a logrecord and then calls
 all the handlers of this logger to handle the record.
 """
 sinfo = none
 if _srcfile:
  #ironpython doesn't track python frames, so findcaller raises an
  #exception on some versions of ironpython. we trap it here so that
  #ironpython can use logging.
  try:
   fn, lno, func, sinfo = self.findcaller(stack_info)
  except valueerror: # pragma: no cover
   fn, lno, func = "(unknown file)", 0, "(unknown function)"
 else: # pragma: no cover
  fn, lno, func = "(unknown file)", 0, "(unknown function)"
 if exc_info:
  if isinstance(exc_info, baseexception):
   exc_info = (type(exc_info), exc_info, exc_info.__traceback__)
  elif not isinstance(exc_info, tuple):
   exc_info = sys.exc_info()
 record = self.makerecord(self.name, level, fn, lno, msg, args,
        exc_info, func, extra, sinfo)
 self.handle(record)

最后两行:

生成日志记录:

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record = self.makerecord(self.name, level, fn, lno, msg, args, exc_info, func, extra, sinfo)

处理日志记录

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self.handle(record)

2 生成日志记录:

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def makerecord(self, name, level, fn, lno, msg, args, exc_info,
    func=none, extra=none, sinfo=none):
 """
 a factory method which can be overridden in subclasses to create
 specialized logrecords.
 """
 rv = _logrecordfactory(name, level, fn, lno, msg, args, exc_info, func,
       sinfo)
 if extra is not none:
  for key in extra:
   if (key in ["message", "asctime"]) or (key in rv.__dict__):
    raise keyerror("attempt to overwrite %r in logrecord" % key)
   rv.__dict__[key] = extra[key]
 return rv

调用_logrecordfactory初始化一个日志记录实例,_logrecordfactory 其实就是logrecord类,初始化时,可能包含logger的name, level、调用的函数、行号、日志字符串、模板参数、堆栈信息等。

再看extra信息,extra到底有何用?现在从代码中可以看到,只是更新到生成的日志记录实例的__dict__中去.猜测:肯定会在生成最终的日志字符串的时候会用到。继续往下看。

3 处理日志记录self.handle(record):

logger继承自filterer,

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def handle(self, record):
 """
 call the handlers for the specified record.
 
 this method is used for unpickled records received from a socket, as
 well as those created locally. logger-level filtering is applied.
 """
 if (not self.disabled) and self.filter(record):
  self.callhandlers(record)

3.1 if语句中有一self.filter(record)的判断,看函数名,是来筛选是否要继续处理消息的,其核心源码如下:

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def filter(self, record):
 """
 determine if a record is loggable by consulting all the filters.
 
 the default is to allow the record to be logged; any filter can veto
 this and the record is then dropped. returns a zero value if a record
 is to be dropped, else non-zero.
 
 .. versionchanged:: 3.2
 
  allow filters to be just callables.
 """
 rv = true
 for f in self.filters:
  if hasattr(f, 'filter'):
   result = f.filter(record)
  else:
   result = f(record) # assume callable - will raise if not
  if not result:
   rv = false
   break
 return rv

可以看到, 如果在handler中的filter中如果有返回为false或空,则会屏蔽对应的record,返回true或部位空的值,则会将record放行。那么我们就可以自定义自己的filter。

3.2 让logger中所有的handles去处理record:

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def callhandlers(self, record):
  """
  pass a record to all relevant handlers.
 
  loop through all handlers for this logger and its parents in the
  logger hierarchy. if no handler was found, output a one-off error
  message to sys.stderr. stop searching up the hierarchy whenever a
  logger with the "propagate" attribute set to zero is found - that
  will be the last logger whose handlers are called.
  """
  c = self
  found = 0
  while c:
   for hdlr in c.handlers:
    found = found + 1
    if record.levelno >= hdlr.level:
     hdlr.handle(record)
   if not c.propagate:
    c = none #break out
   else:
    c = c.parent
  if (found == 0):
   if lastresort:
    if record.levelno >= lastresort.level:
     lastresort.handle(record)
   elif raiseexceptions and not self.manager.emittednohandlerwarning:
    sys.stderr.write("no handlers could be found for logger"
         " \"%s\"\n" % self.name)
    self.manager.emittednohandlerwarning = true

代码中会去循环调用当前logger的所有handlers去处理record,for循环部分,之后,如果当前的logger的propagate的值为false或空,则不向logger的父logger传递,即向上传递。

4. handler 中的 handler(record) 部分:

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def handle(self, record):
  """
  conditionally emit the specified logging record.
 
  emission depends on filters which may have been added to the handler.
  wrap the actual emission of the record with acquisition/release of
  the i/o thread lock. returns whether the filter passed the record for
  emission.
  """
  rv = self.filter(record)
  if rv:
   self.acquire()
   try:
    self.emit(record)
   finally:
    self.release()
  return rv

可以看到, handler在处理record时, 会去加锁,然后调用self.emit(record)方法去处理。

4.1 emit(record)

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def emit(self, record):
  """
  do whatever it takes to actually log the specified logging record.
 
  this version is intended to be implemented by subclasses and so
  raises a notimplementederror.
  """
  raise notimplementederror('emit must be implemented '
         'by handler subclasses')

看到需要由子类去实现,以streamhandler为例子:

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def emit(self, record):
  """
  emit a record.
 
  if a formatter is specified, it is used to format the record.
  the record is then written to the stream with a trailing newline. if
  exception information is present, it is formatted using
  traceback.print_exception and appended to the stream. if the stream
  has an 'encoding' attribute, it is used to determine how to do the
  output to the stream.
  """
  try:
   msg = self.format(record)
   stream = self.stream
   stream.write(msg)
   stream.write(self.terminator)
   self.flush()
  except exception:
   self.handleerror(record)

4.2 handler.format(record):

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def format(self, record):
 """
 format the specified record.
 
 if a formatter is set, use it. otherwise, use the default formatter
 for the module.
 """
 if self.formatter:
  fmt = self.formatter
 else:
  fmt = _defaultformatter
 return fmt.format(record)

如果handler有自定义的formatter就用自定义的,如果没有则用默认的formatter的实例, 初始化元源码为:

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def __init__(self, fmt=none, datefmt=none, style='%'):
 """
 initialize the formatter with specified format strings.
 
 initialize the formatter either with the specified format string, or a
 default as described above. allow for specialized date formatting with
 the optional datefmt argument (if omitted, you get the iso8601 format).
 
 use a style parameter of '%', '{' or '$' to specify that you want to
 use one of %-formatting, :meth:`str.format` (``{}``) formatting or
 :class:`string.template` formatting in your format string.
 
 .. versionchanged:: 3.2
  added the ``style`` parameter.
 """
 if style not in _styles:
  raise valueerror('style must be one of: %s' % ','.join(
       _styles.keys()))
 self._style = _styles[style][0](fmt)
 self._fmt = self._style._fmt
 self.datefmt = datefmt

有三个参数:

  • fmt: 格式化模板
  • datefmt: 时间格式化参数
  • style: 日志格式化的样式。

style有三种:

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_styles = {
 '%': (percentstyle, basic_format),
 '{': (strformatstyle, '{levelname}:{name}:{message}'),
 '$': (stringtemplatestyle, '${levelname}:${name}:${message}'),

可以看出对应到:% 操作符的格式化, format方法的格式化以及template的格式化。

formatter的format方法源码为:

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def format(self, record):
 """
 format the specified record as text.
 the record's attribute dictionary is used as the operand to a
 string formatting operation which yields the returned string.
 before formatting the dictionary, a couple of preparatory steps
 are carried out. the message attribute of the record is computed
 using logrecord.getmessage(). if the formatting string uses the
 time (as determined by a call to usestime(), formattime() is
 called to format the event time. if there is exception information,
 it is formatted using formatexception() and appended to the message.
 """
 record.message = record.getmessage()
 if self.usestime():
  record.asctime = self.formattime(record, self.datefmt)
 s = self.formatmessage(record)
 if record.exc_info:
  # cache the traceback text to avoid converting it multiple times
  # (it's constant anyway)
  if not record.exc_text:
   record.exc_text = self.formatexception(record.exc_info)
 if record.exc_text:
  if s[-1:] != "\n":
   s = s + "\n"
  s = s + record.exc_text
 if record.stack_info:
  if s[-1:] != "\n":
   s = s + "\n"
  s = s + self.formatstack(record.stack_info)

看到会调用record.getmessage(),这里仅仅是获取我们需要的日志信息。

之后会调用s = self.formatmessage(record):

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def formatmessage(self, record):
 return self._style.format(record)

其实是调用了当前style的format方法,以%这一类型为例percentstyle:

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class percentstyle(object):
 
 default_format = '%(message)s'
 asctime_format = '%(asctime)s'
 asctime_search = '%(asctime)'
 
 def __init__(self, fmt):
  self._fmt = fmt or self.default_format
 
 def usestime(self):
  return self._fmt.find(self.asctime_search) >= 0
 
 def format(self, record):
  return self._fmt % record.__dict__

从其中的format方法可以看出,是针对record的__dict__属性中的所有参数进行格式化,这下,就清楚了之前的extra参数是干嘛用的了:可以在formatter中加入自己自定义的一些参数,如固定的用户信息等等。

之后,将最终的message flush到对应的stream里面去就行了,就是整个流程:

详解Python logging调用Logger.info方法的处理过程

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。

原文链接:https://segmentfault.com/a/1190000018119406

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