logging模块学习笔记

一、包结构

核心代码位于__init__.py文件，另外两个文件包含一些扩展

二、关键类

Logger类

数据仓库，用于将日志相关的各种属性收集并格式化。开发者的输入只是属性中的一部分，日志的创建时间、位置、级别等更是收集的重点

Fomatter类

输出模板，用于将Logger实例中指定的属性按照规定的格式转换为字符串，得到的字符串是最终被记录的日志内容

Filter类

过滤器，过滤LogRecord实例，用于判断LogRecord实例是否允许输出

Filterer类

过滤器池，用于串联多个Filter实例，联合过滤LogRecord实例。Handle类和Logger类的父类

Handler类

处理器，Filterer类的子类，将符合条件的LogRecord实例，通过Formatter实例转化为字符串，再输出。Handler类拥有众多子类，线程安全地控制输出是他们的重点作用。

LogRecord类

接口，Filterer类的子类，用于暴露给用户，用户调用生成日志。LogRecord包含一些筛选条件，不符合条件的用户输入会被抛弃

Manager类

接口管理器，用于把Logger实例按照树形结构组织在一起，进而实现Logger实例的复用、Logger实例部分属性的继承

三、调用关系

1、getLogger()调用Manager实例的getLogger()方法，用于获取需要的Logger实例

2、Logger实例是logging模块提供给用户的接口，我们可以通过Logger实例的debug()/info()/warn()/error()/critical()等方法创建日志，除日志级别不同以外，基本没有区别，这里以info()方法为例

3、info()方法会调用isEnabledFor()方法，在isEnabledFor()中，日志将面临人生中的第一次淘汰。Manager实例设置了level属性，规定了整个logging模块的最低日志级别，不低于于这个级别的日志才会被继续处理

4、isEnabledFor()方法会调用getEffectiveLevel()方法。getEffectiveLevel()方法用于获取当前Logger实例的最低日志级别，不低于这个级别的日志才会被继续处理，这是日志人生中的第二次淘汰。isEnabledFor()方法执行完毕，回到info()方法。

5、info()方法继续调用_log()方法，_log()方法尝试获取用户生成这条日志的位置，然后调用makeRecord()方法和handle()方法，info()方法执行完毕。

6、makeRecord()方法将初始化LogRecord()实例，并返回。到现在，新建的日志终于变成了完全体，基本具备了所有可能用到的属性，比如创建时间、创建位置等

7、在handle()方法中，日志面临人生中的第四次淘汰。Logger实例可以通过disabled属性设置为静默模式，处于静默模式的Logger实例将丢弃任意日志。

8、如果Logger不是静默模式，handler()方法将调用filter()方法，filter()方法将尝试让日志依次通过一系列过滤器，通过全部过滤器的日志将被继续处理，这是日志面临的第五次淘汰。

9、handle()方法继续调用callHandlers()方法。Logger实例可能拥有多个并联在一起的处理器（Handle实例），callHandlers()方法是一个分发器，将日志分发给每个处理器进行处理。处理器（Handle实例）也拥有level属性，处理器只会处理级别不小于自己的日志，这是日志面临的第六次淘汰。

10、Handle实例通过handle()方法处理日志，handle()方法调用由父类Filterer继承的filter()方法，filter()方法将尝试让日志依次通过一系列过滤器，通过全部过滤器的日志将被继续处理，这是日志面临的第七次淘汰。

11、handle()方法将调用emit()方法处理活到现在的日志，emit()方法按照Formatter实例规定的格式将LogRecord实例转换为字符串，在这里，日志由完全体变成了最终形态，继而被输出至文件、屏幕等位置。日志的苦难人生终于结束了。

四、一些没有提及的细节

1、Manage和Logger

每个Logger实例都拥有name属性，name属性是一个类似于a.b.c的字符串，Manage实例通过name属性将Logger组织成一个树形结构，并且为树形结构默认设置了根节点。

树形结构可以通过name属性唯一标识Logger实例，有利于代码中复用Logger实例；树形结构还可以帮助实现一些Logger属性的继承，比如level属性、Logger实例拥有的处理器（Handle实例），让代码更简洁，比如Elasticsearch包等使用logging模块输出日志，其专用的Logger实例未设置level字段，继承根节点的level属性，通过设置根节点的level属性，可以轻松提高此类包的输出日志最低等级

2、Filter、Filterer、Handle和Logger

Filter是过滤器，Filterer是过滤器池，过滤器池中的过滤器相互串联。Handle和Logger是Filterer的子类，因此Handle和Logger实例天生拥有filter()方法，天生可以自定义一组过滤器

五、注释源码

# Copyright 2001-2014 by Vinay Sajip. All Rights Reserved.## Permission to use, copy, modify, and distribute this software and its# documentation for any purpose and without fee is hereby granted,# provided that the above copyright notice appear in all copies and that# both that copyright notice and this permission notice appear in# supporting documentation, and that the name of Vinay Sajip# not be used in advertising or publicity pertaining to distribution# of the software without specific, written prior permission.# VINAY SAJIP DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING# ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL# VINAY SAJIP BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR# ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER# IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE."""Logging package for Python. Based on PEP 282 and comments thereto incomp.lang.python.Copyright (C) 2001-2014 Vinay Sajip. All Rights Reserved.To use, simply 'import logging' and log away!"""import sys, os, time, cStringIO, traceback, warnings, weakref, collections__all__ = ['BASIC_FORMAT', 'BufferingFormatter', 'CRITICAL', 'DEBUG', 'ERROR',           'FATAL', 'FileHandler', 'Filter', 'Formatter', 'Handler', 'INFO',           'LogRecord', 'Logger', 'LoggerAdapter', 'NOTSET', 'NullHandler',           'StreamHandler', 'WARN', 'WARNING', 'addLevelName', 'basicConfig',           'captureWarnings', 'critical', 'debug', 'disable', 'error',           'exception', 'fatal', 'getLevelName', 'getLogger', 'getLoggerClass',           'info', 'log', 'makeLogRecord', 'setLoggerClass', 'warn', 'warning']try:    import codecsexcept ImportError:    codecs = Nonetry:    import thread    import threadingexcept ImportError:    thread = None__author__  = "Vinay Sajip <[e-mail]>"__status__  = "production"# Note: the attributes below are no longer maintained.__version__ = "0.5.1.2"__date__    = "07 February 2010"#---------------------------------------------------------------------------#   Miscellaneous module data#---------------------------------------------------------------------------try:    unicode    _unicode = Trueexcept NameError:    _unicode = False# next bit filched from 1.5.2's inspect.pydef currentframe():    """Return the frame object for the caller's stack frame.""""""返回currentframe()函数的调用者在函数栈中的结构"""    try:        raise Exception    except:        return sys.exc_info()[2].tb_frame.f_back# 如果支持sys._getframe()方法，则返回currentframe()函数的调用者的调用者的调用者在函数栈中的结构。指定上3层调用者，是作者根据currentframe()函数在logging模块中的使用场景选择的，为的是在利用currentframe()函数获取logging模块调用者函数栈结构时更高效。if hasattr(sys, '_getframe'): currentframe = lambda: sys._getframe(3)# done filching## _srcfile is used when walking the stack to check when we've got the first# caller stack frame.# 记录当前文件所在路径_srcfile = os.path.normcase(currentframe.__code__.co_filename)# _srcfile is only used in conjunction with sys._getframe().# To provide compatibility with older versions of Python, set _srcfile# to None if _getframe() is not available; this value will prevent# findCaller() from being called.#if not hasattr(sys, "_getframe"):#    _srcfile = None##_startTime is used as the base when calculating the relative time of events## logging模块第一次被调用的时间戳_startTime = time.time()##raiseExceptions is used to see if exceptions during handling should be#propagated## 处理日志时触发的异常是否忽略，忽略设为0raiseExceptions = 1## If you don't want threading information in the log, set this to zero#logThreads = 1## If you don't want multiprocessing information in the log, set this to zero#logMultiprocessing = 1## If you don't want process information in the log, set this to zero#logProcesses = 1#---------------------------------------------------------------------------#   Level related stuff#---------------------------------------------------------------------------## Default levels and level names, these can be replaced with any positive set# of values having corresponding names. There is a pseudo-level, NOTSET, which# is only really there as a lower limit for user-defined levels. Handlers and# loggers are initialized with NOTSET so that they will log all messages, even# at user-defined levels.## 使用数字表示日志级别，方便比较；将表示级别的数字定义为常亮，方便使用CRITICAL = 50FATAL = CRITICALERROR = 40WARNING = 30WARN = WARNINGINFO = 20DEBUG = 10NOTSET = 0# 级别名和级别数值互相映射，便于查找_levelNames = {    CRITICAL : 'CRITICAL',    ERROR : 'ERROR',    WARNING : 'WARNING',    INFO : 'INFO',    DEBUG : 'DEBUG',    NOTSET : 'NOTSET',    'CRITICAL' : CRITICAL,    'ERROR' : ERROR,    'WARN' : WARNING,    'WARNING' : WARNING,    'INFO' : INFO,    'DEBUG' : DEBUG,    'NOTSET' : NOTSET,}def getLevelName(level):    """    Return the textual representation of logging level 'level'.    If the level is one of the predefined levels (CRITICAL, ERROR, WARNING,    INFO, DEBUG) then you get the corresponding string. If you have    associated levels with names using addLevelName then the name you have    associated with 'level' is returned.    If a numeric value corresponding to one of the defined levels is passed    in, the corresponding string representation is returned.    Otherwise, the string "Level %s" % level is returned.    """"""由级别名获取级别数值"""    return _levelNames.get(level, ("Level %s" % level))def addLevelName(level, levelName):    """    Associate 'levelName' with 'level'.    This is used when converting levels to text during message formatting.    """"""自定义日志级别"""    _acquireLock()    try:    #unlikely to cause an exception, but you never know...        _levelNames[level] = levelName        _levelNames[levelName] = level    finally:        _releaseLock()def _checkLevel(level):"""检测level有效性。level为数字，无论该数字是否在_levelNames中定义，均有效；level为字符串，_levelNames中定义的日志级别名有效；其他level取值无效"""    if isinstance(level, (int, long)):        rv = level    elif str(level) == level:        if level not in _levelNames:            raise ValueError("Unknown level: %r" % level)        rv = _levelNames[level]    else:        raise TypeError("Level not an integer or a valid string: %r" % level)    return rv#---------------------------------------------------------------------------#   Thread-related stuff#---------------------------------------------------------------------------##_lock is used to serialize access to shared data structures in this module.#This needs to be an RLock because fileConfig() creates and configures#Handlers, and so might arbitrary user threads. Since Handler code updates the#shared dictionary _handlers, it needs to acquire the lock. But if configuring,#the lock would already have been acquired - so we need an RLock.#The same argument applies to Loggers and Manager.loggerDict.## 模块级别锁，用于模块级别的公用数据if thread:    _lock = threading.RLock()else:    _lock = Nonedef _acquireLock():    """    Acquire the module-level lock for serializing access to shared data.    This should be released with _releaseLock().    """    if _lock:        _lock.acquire()def _releaseLock():    """    Release the module-level lock acquired by calling _acquireLock().    """    if _lock:        _lock.release()#---------------------------------------------------------------------------#   The logging record#---------------------------------------------------------------------------class LogRecord(object):    """    A LogRecord instance represents an event being logged.    LogRecord instances are created every time something is logged. They    contain all the information pertinent to the event being logged. The    main information passed in is in msg and args, which are combined    using str(msg) % args to create the message field of the record. The    record also includes information such as when the record was created,    the source line where the logging call was made, and any exception    information to be logged.""""""LogRecord类。包含一条日志的各种信息，用于根据格式要求，生成指定样式的日志字符串    """    def __init__(self, name, level, pathname, lineno,                 msg, args, exc_info, func=None):        """        Initialize a logging record with interesting information.        """        ct = time.time()        self.name = name        self.msg = msg        #        # The following statement allows passing of a dictionary as a sole        # argument, so that you can do something like        #  logging.debug("a %(a)d b %(b)s", {'a':1, 'b':2})        # Suggested by Stefan Behnel.        # Note that without the test for args[0], we get a problem because        # during formatting, we test to see if the arg is present using        # 'if self.args:'. If the event being logged is e.g. 'Value is %d'        # and if the passed arg fails 'if self.args:' then no formatting        # is done. For example, logger.warn('Value is %d', 0) would log        # 'Value is %d' instead of 'Value is 0'.        # For the use case of passing a dictionary, this should not be a        # problem.        # Issue #21172: a request was made to relax the isinstance check        # to hasattr(args[0], '__getitem__'). However, the docs on string        # formatting still seem to suggest a mapping object is required.        # Thus, while not removing the isinstance check, it does now look        # for collections.Mapping rather than, as before, dict.        if (args and len(args) == 1 and isinstance(args[0], collections.Mapping)            and args[0]):            args = args[0]        self.args = args        self.levelname = getLevelName(level)        self.levelno = level        self.pathname = pathname  # logging调用者所在文件完整路径        try:            self.filename = os.path.basename(pathname)  # logging调用者完整文件名            self.module = os.path.splitext(self.filename)[0]  # logging调用者文件名，不带扩展名        except (TypeError, ValueError, AttributeError):            self.filename = pathname            self.module = "Unknown module"        self.exc_info = exc_info        self.exc_text = None      # used to cache the traceback text        self.lineno = lineno        self.funcName = func  # 用户调用Logger实例所在函数名        self.created = ct        self.msecs = (ct - long(ct)) * 1000        self.relativeCreated = (self.created - _startTime) * 1000        if logThreads and thread:            self.thread = thread.get_ident()            self.threadName = threading.current_thread().name        else:            self.thread = None            self.threadName = None        if not logMultiprocessing:            self.processName = None        else:            self.processName = 'MainProcess'            mp = sys.modules.get('multiprocessing')            if mp is not None:                # Errors may occur if multiprocessing has not finished loading                # yet - e.g. if a custom import hook causes third-party code                # to run when multiprocessing calls import. See issue 8200                # for an example                try:                    self.processName = mp.current_process().name                except StandardError:                    pass        if logProcesses and hasattr(os, 'getpid'):            self.process = os.getpid()        else:            self.process = None    def __str__(self):        return '<LogRecord: %s, %s, %s, %s, "%s">'%(self.name, self.levelno,            self.pathname, self.lineno, self.msg)    def getMessage(self):        """        Return the message for this LogRecord.        Return the message for this LogRecord after merging any user-supplied        arguments with the message.        """"""用户描述日志内容时可能使用格式化字符串的方式，处理用户需要输出的日志内"""        if not _unicode: #if no unicode support...            msg = str(self.msg)        else:            msg = self.msg            if not isinstance(msg, basestring):                try:                    msg = str(self.msg)                except UnicodeError:                    msg = self.msg      #Defer encoding till later        if self.args:            msg = msg % self.args        return msgdef makeLogRecord(dict):    """    Make a LogRecord whose attributes are defined by the specified dictionary,    This function is useful for converting a logging event received over    a socket connection (which is sent as a dictionary) into a LogRecord    instance.    """"""声明‘空’的LogRecord实例，使用dict.update()方法，强行更新它"""    rv = LogRecord(None, None, "", 0, "", (), None, None)    rv.__dict__.update(dict)    return rv#---------------------------------------------------------------------------#   Formatter classes and functions#---------------------------------------------------------------------------class Formatter(object):    """    Formatter instances are used to convert a LogRecord to text.    Formatters need to know how a LogRecord is constructed. They are    responsible for converting a LogRecord to (usually) a string which can    be interpreted by either a human or an external system. The base Formatter    allows a formatting string to be specified. If none is supplied, the    default value of "%s(message)\\n" is used.    The Formatter can be initialized with a format string which makes use of    knowledge of the LogRecord attributes - e.g. the default value mentioned    above makes use of the fact that the user's message and arguments are pre-    formatted into a LogRecord's message attribute. Currently, the useful    attributes in a LogRecord are described by:    %(name)s            Name of the logger (logging channel)    %(levelno)s         Numeric logging level for the message (DEBUG, INFO,                        WARNING, ERROR, CRITICAL)    %(levelname)s       Text logging level for the message ("DEBUG", "INFO",                        "WARNING", "ERROR", "CRITICAL")    %(pathname)s        Full pathname of the source file where the logging                        call was issued (if available)    %(filename)s        Filename portion of pathname    %(module)s          Module (name portion of filename)    %(lineno)d          Source line number where the logging call was issued                        (if available)    %(funcName)s        Function name    %(created)f         Time when the LogRecord was created (time.time()                        return value)    %(asctime)s         Textual time when the LogRecord was created    %(msecs)d           Millisecond portion of the creation time    %(relativeCreated)d Time in milliseconds when the LogRecord was created,                        relative to the time the logging module was loaded                        (typically at application startup time)    %(thread)d          Thread ID (if available)    %(threadName)s      Thread name (if available)    %(process)d         Process ID (if available)    %(message)s         The result of record.getMessage(), computed just as                        the record is emitted    """"""指定格式，生成包含‘主体内容’+‘附加内容’的完整日志，用户调用logging模块希望输出的是‘主体内容’，调用logging模块的时间、位置等是‘附加内容’具体实现：‘format’ % LogRecord.__dict__基于以上原理，我们可以为LogRecord添加自定义属性，并且在最终结果中得以体现"""    converter = time.localtime    def __init__(self, fmt=None, datefmt=None):        """        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).        """        if fmt:            self._fmt = fmt        else:            self._fmt = "%(message)s"        self.datefmt = datefmt    def formatTime(self, record, datefmt=None):        """        Return the creation time of the specified LogRecord as formatted text.        This method should be called from format() by a formatter which        wants to make use of a formatted time. This method can be overridden        in formatters to provide for any specific requirement, but the        basic behaviour is as follows: if datefmt (a string) is specified,        it is used with time.strftime() to format the creation time of the        record. Otherwise, the ISO8601 format is used. The resulting        string is returned. This function uses a user-configurable function        to convert the creation time to a tuple. By default, time.localtime()        is used; to change this for a particular formatter instance, set the        'converter' attribute to a function with the same signature as        time.localtime() or time.gmtime(). To change it for all formatters,        for example if you want all logging times to be shown in GMT,        set the 'converter' attribute in the Formatter class.        """"""输出本地时间字符串"""        ct = self.converter(record.created)        if datefmt:            s = time.strftime(datefmt, ct)        else:            t = time.strftime("%Y-%m-%d %H:%M:%S", ct)            s = "%s,%03d" % (t, record.msecs)        return s    def formatException(self, ei):        """        Format and return the specified exception information as a string.        This default implementation just uses        traceback.print_exception()        """"""输出触发异常时的函数调用栈相关信息，以字符串形式。ei被赋值为sys.exc_info()函数的返回值"""        sio = cStringIO.StringIO()        traceback.print_exception(ei[0], ei[1], ei[2], None, sio)        s = sio.getvalue()        sio.close()        if s[-1:] == "\n":            s = s[:-1]        return s    def usesTime(self):        """        Check if the format uses the creation time of the record.        """"""判断指定的日志格式中，是否使用到asctime属性（LogRecord实例创建时间）"""        return self._fmt.find("%(asctime)") >= 0    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.        """"""使用‘format’ % LogRecord.__dict__的方式得到用于输出的日志LogRecord实例中部分属性需要先进行处理，比如时间、异常信息、日志主体内容。先处理，将处理结果保存至LogRecord实例再统一格式化，这样的处理更清晰。"""        record.message = record.getMessage()        if self.usesTime():            record.asctime = self.formatTime(record, self.datefmt)        try:            s = self._fmt % record.__dict__        except UnicodeDecodeError as e:            # Issue 25664. The logger name may be Unicode. Try again ...            try:                record.name = record.name.decode('utf-8')                s = self._fmt % record.__dict__            except UnicodeDecodeError:                raise e        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"            try:                s = s + record.exc_text            except UnicodeError:                # Sometimes filenames have non-ASCII chars, which can lead                # to errors when s is Unicode and record.exc_text is str                # See issue 8924.                # We also use replace for when there are multiple                # encodings, e.g. UTF-8 for the filesystem and latin-1                # for a script. See issue 13232.                s = s + record.exc_text.decode(sys.getfilesystemencoding(),                                               'replace')        return s##   The default formatter to use when no other is specified#_defaultFormatter = Formatter()class BufferingFormatter(object):    """    A formatter suitable for formatting a number of records.    """"""以相同的格式处理一组LogRecord实例，并且可以再开头和结尾添加注脚"""    def __init__(self, linefmt=None):        """        Optionally specify a formatter which will be used to format each        individual record.        """        if linefmt:            self.linefmt = linefmt        else:            self.linefmt = _defaultFormatter    def formatHeader(self, records):        """        Return the header string for the specified records.        """        return ""    def formatFooter(self, records):        """        Return the footer string for the specified records.        """        return ""    def format(self, records):        """        Format the specified records and return the result as a string.        """        rv = ""        if len(records) > 0:            rv = rv + self.formatHeader(records)            for record in records:                rv = rv + self.linefmt.format(record)            rv = rv + self.formatFooter(records)        return rv#---------------------------------------------------------------------------#   Filter classes and functions#---------------------------------------------------------------------------class Filter(object):    """    Filter instances are used to perform arbitrary filtering of LogRecords.    Loggers and Handlers can optionally use Filter instances to filter    records as desired. The base filter class only allows events which are    below a certain point in the logger hierarchy. For example, a filter    initialized with "A.B" will allow events logged by loggers "A.B",    "A.B.C", "A.B.C.D", "A.B.D" etc. but not "A.BB", "B.A.B" etc. If    initialized with the empty string, all events are passed.    """"""过滤器。filter()方法可以按照需求重写，默认按照name属性判断LogRecord实例是否通过筛选"""    def __init__(self, name=''):        """        Initialize a filter.        Initialize with the name of the logger which, together with its        children, will have its events allowed through the filter. If no        name is specified, allow every event.        """        self.name = name        self.nlen = len(name)    def filter(self, record):        """        Determine if the specified record is to be logged.        Is the specified record to be logged? Returns 0 for no, nonzero for        yes. If deemed appropriate, the record may be modified in-place.        """        if self.nlen == 0:            return 1        elif self.name == record.name:            return 1        elif record.name.find(self.name, 0, self.nlen) != 0:            return 0        return (record.name[self.nlen] == ".")class Filterer(object):    """    A base class for loggers and handlers which allows them to share    common code.    """"""过滤器容器。容纳多个Filter实例，并提供方法判断LogRecord实例是否能通过全部Filter实例的筛选"""    def __init__(self):        """        Initialize the list of filters to be an empty list.        """        self.filters = []    def addFilter(self, filter):        """        Add the specified filter to this handler.        """        if not (filter in self.filters):            self.filters.append(filter)    def removeFilter(self, filter):        """        Remove the specified filter from this handler.        """        if filter in self.filters:            self.filters.remove(filter)    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.        """        rv = 1        for f in self.filters:            if not f.filter(record):                rv = 0                break        return rv#---------------------------------------------------------------------------#   Handler classes and functions#---------------------------------------------------------------------------_handlers = weakref.WeakValueDictionary()  #map of handler names to handlers_handlerList = [] # added to allow handlers to be removed in reverse of order initializeddef _removeHandlerRef(wr):    """    Remove a handler reference from the internal cleanup list.    """"""将Hander实例的弱引用从_handlerList中删除，Handler实例被清理时被调用"""    # This function can be called during module teardown, when globals are    # set to None. It can also be called from another thread. So we need to    # pre-emptively grab the necessary globals and check if they're None,    # to prevent race conditions and failures during interpreter shutdown.    acquire, release, handlers = _acquireLock, _releaseLock, _handlerList    if acquire and release and handlers:        acquire()        try:            if wr in handlers:                handlers.remove(wr)        finally:            release()def _addHandlerRef(handler):    """    Add a handler to the internal cleanup list using a weak reference.    """"""为Handler实例创建弱引用，保存至_handlerList。以便程序退出时清理，释放资源"""    _acquireLock()    try:        _handlerList.append(weakref.ref(handler, _removeHandlerRef))    finally:        _releaseLock()class Handler(Filterer):    """    Handler instances dispatch logging events to specific destinations.    The base handler class. Acts as a placeholder which defines the Handler    interface. Handlers can optionally use Formatter instances to format    records as desired. By default, no formatter is specified; in this case,    the 'raw' message as determined by record.message is logged.    """"""输出处理器。每个Handler实例代表一条输出途径，控制着日志能否输出、如何输出"""    def __init__(self, level=NOTSET):        """        Initializes the instance - basically setting the formatter to None        and the filter list to empty.        """        Filterer.__init__(self)        self._name = None        self.level = _checkLevel(level)        self.formatter = None        # Add the handler to the global _handlerList (for cleanup on shutdown)# 每个Handler实例创建时都创建并保留指向自己的弱引用，以便程序退出时检查清理。Handler实例多包含文件句柄等系统资源，不及时释放可能导致一些问题。        _addHandlerRef(self)        self.createLock()    def get_name(self):        return self._name    def set_name(self, name):# 同名handler覆盖        _acquireLock()        try:            if self._name in _handlers:                del _handlers[self._name]            self._name = name            if name:                _handlers[name] = self        finally:            _releaseLock()    # 通过property函数，我们可以使用"."操作符，像操作属性一样调用get/set方法name = property(get_name, set_name)# Handler实例被同类LogRecord实例公用，Handler实例的日志输出通道实际也是被公用的，因此需要实例级别锁来保证线程安全    def createLock(self):        """        Acquire a thread lock for serializing access to the underlying I/O.        """        if thread:            self.lock = threading.RLock()        else:            self.lock = None    def acquire(self):        """        Acquire the I/O thread lock.        """        if self.lock:            self.lock.acquire()    def release(self):        """        Release the I/O thread lock.        """        if self.lock:            self.lock.release()    def setLevel(self, level):        """        Set the logging level of this handler.        """        self.level = _checkLevel(level)    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)    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.        """"""输出日志的方法。由子类具体实现。"""        raise NotImplementedError('emit must be implemented '                                  'by Handler subclasses')    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.        """"""日志能够输出的第四层过滤条件：日志级别是否满足handler中过滤器的要求处于阻塞状态，知道获取日志输出通道使用权后才可以输出，输出完毕释放通道使用权"""        rv = self.filter(record)        if rv:            self.acquire()            try:                self.emit(record)            finally:                self.release()        return rv    def setFormatter(self, fmt):        """        Set the formatter for this handler.        """        self.formatter = fmt    def flush(self):        """        Ensure all logging output has been flushed.        This version does nothing and is intended to be implemented by        subclasses.        """        pass    def close(self):        """        Tidy up any resources used by the handler.        This version removes the handler from an internal map of handlers,        _handlers, which is used for handler lookup by name. Subclasses        should ensure that this gets called from overridden close()        methods.        """        #get the module data lock, as we're updating a shared structure.        _acquireLock()        try:    #unlikely to raise an exception, but you never know...            if self._name and self._name in _handlers:                del _handlers[self._name]        finally:            _releaseLock()    def handleError(self, record):        """        Handle errors which occur during an emit() call.        This method should be called from handlers when an exception is        encountered during an emit() call. If raiseExceptions is false,        exceptions get silently ignored. This is what is mostly wanted        for a logging system - most users will not care about errors in        the logging system, they are more interested in application errors.        You could, however, replace this with a custom handler if you wish.        The record which was being processed is passed in to this method.        """"""日志输出过程中的异常处理：不可以打断程序正常运行；logging未被设置为静默状态时，尝试向标准错误流输出异常内容"""        if raiseExceptions and sys.stderr:  # see issue 13807            ei = sys.exc_info()            try:                traceback.print_exception(ei[0], ei[1], ei[2],                                          None, sys.stderr)                sys.stderr.write('Logged from file %s, line %s\n' % (                                 record.filename, record.lineno))            except IOError:                pass    # see issue 5971            finally:                del eiclass StreamHandler(Handler):    """    A handler class which writes logging records, appropriately formatted,    to a stream. Note that this class does not close the stream, as    sys.stdout or sys.stderr may be used.    """"""Handler类的子类。关注emit()方法即可。"""    def __init__(self, stream=None):        """        Initialize the handler.        If stream is not specified, sys.stderr is used.        """        Handler.__init__(self)        if stream is None:            stream = sys.stderr        self.stream = stream    def flush(self):        """        Flushes the stream.        """        self.acquire()        try:            if self.stream and hasattr(self.stream, "flush"):                self.stream.flush()        finally:            self.release()    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.        """"""关注对编码的处理"""        try:            msg = self.format(record)            stream = self.stream            fs = "%s\n"            if not _unicode: #if no unicode support...                stream.write(fs % msg)            else:                try:                    if (isinstance(msg, unicode) and                        getattr(stream, 'encoding', None)):                        ufs = u'%s\n'                        try:                            stream.write(ufs % msg)                        except UnicodeEncodeError:                            #Printing to terminals sometimes fails. For example,                            #with an encoding of 'cp1251', the above write will                            #work if written to a stream opened or wrapped by                            #the codecs module, but fail when writing to a                            #terminal even when the codepage is set to cp1251.                            #An extra encoding step seems to be needed.                            stream.write((ufs % msg).encode(stream.encoding))                    else:                        stream.write(fs % msg)                except UnicodeError:                    stream.write(fs % msg.encode("UTF-8"))            self.flush()        except (KeyboardInterrupt, SystemExit):            raise        except:            self.handleError(record)class FileHandler(StreamHandler):    """    A handler class which writes formatted logging records to disk files.    """"""StreamHeadler类的子类。关注_open()方法，关注对编码的处理"""    def __init__(self, filename, mode='a', encoding=None, delay=0):        """        Open the specified file and use it as the stream for logging.        """        #keep the absolute path, otherwise derived classes which use this        #may come a cropper when the current directory changes        if codecs is None:            encoding = None        self.baseFilename = os.path.abspath(filename)        self.mode = mode        self.encoding = encoding        self.delay = delay        if delay:            #We don't open the stream, but we still need to call the            #Handler constructor to set level, formatter, lock etc.            Handler.__init__(self)            self.stream = None        else:            StreamHandler.__init__(self, self._open())    def close(self):        """        Closes the stream.        """        self.acquire()        try:            try:                if self.stream:                    try:                        self.flush()                    finally:                        stream = self.stream                        self.stream = None                        if hasattr(stream, "close"):                            stream.close()            finally:                # Issue #19523: call unconditionally to                # prevent a handler leak when delay is set                StreamHandler.close(self)        finally:            self.release()    def _open(self):        """        Open the current base file with the (original) mode and encoding.        Return the resulting stream.        """        if self.encoding is None:            stream = open(self.baseFilename, self.mode)        else:            stream = codecs.open(self.baseFilename, self.mode, self.encoding)        return stream    def emit(self, record):        """        Emit a record.        If the stream was not opened because 'delay' was specified in the        constructor, open it before calling the superclass's emit.        """        if self.stream is None:            self.stream = self._open()        StreamHandler.emit(self, record)#---------------------------------------------------------------------------#   Manager classes and functions#---------------------------------------------------------------------------class PlaceHolder(object):    """    PlaceHolder instances are used in the Manager logger hierarchy to take    the place of nodes for which no loggers have been defined. This class is    intended for internal use only and not as part of the public API.    """"""占位符。logging模块将所有Logger实例以嵌套的关系组织在一起，Logger实例的部分属性按照嵌套关系向上继承。声明Logger实例时并不需要按照嵌套关系一层层声明全部需要的Logger实例，跨级声明时，原来不存在的上层Logger实例使用PlaceHolder实例替代嵌套关系使用类似于Python/Java Package的形式，即靠name属性在逻辑上定义嵌套关系，而不依赖链表指针。但Logger实例中包含指向上层第一个Logger实例的指针（parent属性）。通过PlaceHolder实例，在插入Logger实例时，可以比较方便得处理上下层嵌套关系。"""    def __init__(self, alogger):        """        Initialize with the specified logger being a child of this placeholder.        """        #self.loggers = [alogger]        1self.loggerMap = { alogger : None }  # key为位于占位符下层的Logger实例的引用。PlaceHolder被实例化，必然存在一个Logger实例跨级创建，该Logger实例必然位于此PlaceHolder实例的下层、    def append(self, alogger):        """        Add the specified logger as a child of this placeholder.        """        #if alogger not in self.loggers:        if alogger not in self.loggerMap:            #self.loggers.append(alogger)            self.loggerMap[alogger] = None##   Determine which class to use when instantiating loggers.#_loggerClass = Nonedef setLoggerClass(klass):    """    Set the class to be used when instantiating a logger. The class should    define __init__() such that only a name argument is required, and the    __init__() should call Logger.__init__()    """"""设置默认logger类"""    if klass != Logger:        if not issubclass(klass, Logger):            raise TypeError("logger not derived from logging.Logger: "                            + klass.__name__)    global _loggerClass    _loggerClass = klassdef getLoggerClass():    """    Return the class to be used when instantiating a logger.    """    return _loggerClassclass Manager(object):    """    There is [under normal circumstances] just one Manager instance, which    holds the hierarchy of loggers.    """"""日志实例（Logger）管理类。有且仅有一个Manager实例，用于维护Logger实例的嵌套关系。"""    def __init__(self, rootnode):        """        Initialize the manager with the root node of the logger hierarchy.        """        self.root = rootnode  # 根节点        self.disable = 0  # 限制可输出的日志级别。只有级别高于disable属性的日志才可能被输出        self.emittedNoHandlerWarning = 0  # 标记位，标记是否有logger存在无handler可用，并且异常被输出至sys.stderr的情况        self.loggerDict = {}  # 维护全部Logger实例，Logger.name: Logger        self.loggerClass = None  # 指定创建日志实例时使用的类，优先级最高，设置后可以覆盖_loggerClass    def getLogger(self, name):        """        Get a logger with the specified name (channel name), creating it        if it doesn't yet exist. This name is a dot-separated hierarchical        name, such as "a", "a.b", "a.b.c" or similar.        If a PlaceHolder existed for the specified name [i.e. the logger        didn't exist but a child of it did], replace it with the created        logger and fix up the parent/child references which pointed to the        placeholder to now point to the logger.        """"""根据name，在self.loggerDict中搜索并返回logger实例。不存在则先创建并插入再返回；存在但不是Logger实例，是PlaceHolder实例，则先创建并替换再返回"""        rv = None        if not isinstance(name, basestring):            raise TypeError('A logger name must be string or Unicode')        if isinstance(name, unicode):            name = name.encode('utf-8')        _acquireLock()        try:            if name in self.loggerDict:                rv = self.loggerDict[name]                if isinstance(rv, PlaceHolder):                    ph = rv                    rv = (self.loggerClass or _loggerClass)(name)                    rv.manager = self                    self.loggerDict[name] = rv                    self._fixupChildren(ph, rv)                    self._fixupParents(rv)            else:                rv = (self.loggerClass or _loggerClass)(name)                rv.manager = self                self.loggerDict[name] = rv                self._fixupParents(rv)        finally:            _releaseLock()        return rv    def setLoggerClass(self, klass):        """        Set the class to be used when instantiating a logger with this Manager.        """"""类似于全局方法setLoggerClass()"""        if klass != Logger:            if not issubclass(klass, Logger):                raise TypeError("logger not derived from logging.Logger: "                                + klass.__name__)        self.loggerClass = klass    def _fixupParents(self, alogger):        """        Ensure that there are either loggers or placeholders all the way        from the specified logger to the root of the logger hierarchy.        """"""在嵌套结构中向上修复因插入新Logger实例导致的错误：1、延嵌套结构向上，完善嵌套结构的每一层，不存在的就创建PlaceHolder实例2、新节点的parent属性指向眼嵌套结构向上第一个Logger对象，没有找到则指向根节点3、将新节点添加为新节点及其parent属性指向节点间所有PlaceHolder实例的子节点"""        name = alogger.name        i = name.rfind(".")        rv = None        while (i > 0) and not rv:            substr = name[:i]            if substr not in self.loggerDict:                self.loggerDict[substr] = PlaceHolder(alogger)            else:                obj = self.loggerDict[substr]                if isinstance(obj, Logger):                    rv = obj                else:                    assert isinstance(obj, PlaceHolder)                    obj.append(alogger)            i = name.rfind(".", 0, i - 1)        if not rv:            rv = self.root        alogger.parent = rv    def _fixupChildren(self, ph, alogger):        """        Ensure that children of the placeholder ph are connected to the        specified logger.使用logger实例替换层次结构中的占位符以后，要注意修改被替换占位符子节点的parent属性，毕竟parent属性指向的是它层次机构之上第一个logger实例修改logger实例的parent属性应该只是顺便写一下，毕竟无论替换还是插入logger，都需要调用_fixupParents()方法，而在_fixupParents()方法中做了类似的事情        """"""在嵌套结构中向下修复因插入新Logger实例导致的错误：1、新插入Logger实例未取代原有PlaceHolder实例，无需调用该方法2、嵌套结构向下第一个Logger对象的parent属性指向新插入的Logger实例"""        name = alogger.name        namelen = len(name)        for c in ph.loggerMap.keys():            #The if means ... if not c.parent.name.startswith(nm)            if c.parent.name[:namelen] != name:                alogger.parent = c.parent                c.parent = alogger#---------------------------------------------------------------------------#   Logger classes and functions#---------------------------------------------------------------------------class Logger(Filterer):    """    Instances of the Logger class represent a single logging channel. A    "logging channel" indicates an area of an application. Exactly how an    "area" is defined is up to the application developer. Since an    application can have any number of areas, logging channels are identified    by a unique string. Application areas can be nested (e.g. an area    of "input processing" might include sub-areas "read CSV files", "read    XLS files" and "read Gnumeric files"). To cater for this natural nesting,    channel names are organized into a namespace hierarchy where levels are    separated by periods, much like the Java or Python package namespace. So    in the instance given above, channel names might be "input" for the upper    level, and "input.csv", "input.xls" and "input.gnu" for the sub-levels.    There is no arbitrary limit to the depth of nesting.    """"""日志类。logging模块暴露给用户的接口类，不同Logger实例在Manager实例中以嵌套形式组织，以便level、handlers等属性向上继承。"""    def __init__(self, name, level=NOTSET):        """        Initialize the logger with a name and an optional level.        """        Filterer.__init__(self)        self.name = name        self.level = _checkLevel(level)        self.parent = None  # 上层Logger实例        self.propagate = 1  # logger是否允许递归像层次结构中的上一层获取handler        self.handlers = []        self.disabled = 0  # logger是否允许输出日志    def setLevel(self, level):        """        Set the logging level of this logger.        """        self.level = _checkLevel(level)    def debug(self, msg, *args, **kwargs):        """        Log 'msg % args' with severity 'DEBUG'.        To pass exception information, use the keyword argument exc_info with        a true value, e.g.        logger.debug("Houston, we have a %s", "thorny problem", exc_info=1)        """        if self.isEnabledFor(DEBUG):            self._log(DEBUG, msg, args, **kwargs)    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)    def warning(self, msg, *args, **kwargs):        """        Log 'msg % args' with severity 'WARNING'.        To pass exception information, use the keyword argument exc_info with        a true value, e.g.        logger.warning("Houston, we have a %s", "bit of a problem", exc_info=1)        """        if self.isEnabledFor(WARNING):            self._log(WARNING, msg, args, **kwargs)    warn = warning    def error(self, msg, *args, **kwargs):        """        Log 'msg % args' with severity 'ERROR'.        To pass exception information, use the keyword argument exc_info with        a true value, e.g.        logger.error("Houston, we have a %s", "major problem", exc_info=1)        """        if self.isEnabledFor(ERROR):            self._log(ERROR, msg, args, **kwargs)    def exception(self, msg, *args, **kwargs):        """        Convenience method for logging an ERROR with exception information.        """        kwargs['exc_info'] = 1        self.error(msg, *args, **kwargs)    def critical(self, msg, *args, **kwargs):        """        Log 'msg % args' with severity 'CRITICAL'.        To pass exception information, use the keyword argument exc_info with        a true value, e.g.        logger.critical("Houston, we have a %s", "major disaster", exc_info=1)        """        if self.isEnabledFor(CRITICAL):            self._log(CRITICAL, msg, args, **kwargs)    fatal = critical    def log(self, level, msg, *args, **kwargs):        """        Log 'msg % args' with the integer severity 'level'.        To pass exception information, use the keyword argument exc_info with        a true value, e.g.        logger.log(level, "We have a %s", "mysterious problem", exc_info=1)        """"""创建日志。参数含义：level——日志级别，数字，可以是默认级别、自定义级别甚至未定义的级别，未定义级别在声明LogRecord实例时可能会有问题msg——日志主体内容或主体内容的格式args——填充主体内容格式的参数kwargs——仅支持exc_info和extra两个参数。exc_info为非0值时输出的日志将附带上一个被输出的异常的函数调用关系；extta被用来扩展LogRecord实例的属性debug()/info()/warn()/warning()/error()/exception()/critical()/fatal()是log()函数使用默认级别的具体形式而已"""        if not isinstance(level, int):            if raiseExceptions:                raise TypeError("level must be an integer")            else:                return        if self.isEnabledFor(level):            self._log(level, msg, args, **kwargs)    def findCaller(self):        """        Find the stack frame of the caller so that we can note the source        file name, line number and function name.        """"""由函数调用栈中logging模块的某一层开始，向调用者方向追溯，通过比对所在文件名判断是否跳出logging模块，第一层跳出logging模块的函数即为logging模块的调用者，返回调用者的文件名、行号、函数名"""        f = currentframe()        #On some versions of IronPython, currentframe() returns None if        #IronPython isn't run with -X:Frames.        if f is not None:            f = f.f_back        rv = "(unknown file)", 0, "(unknown function)"        while hasattr(f, "f_code"):            co = f.f_code            filename = os.path.normcase(co.co_filename)            if filename == _srcfile:                f = f.f_back                continue            rv = (co.co_filename, f.f_lineno, co.co_name)            break        return rv    def makeRecord(self, name, level, fn, lno, msg, args, exc_info, func=None, extra=None):        """        A factory method which can be overridden in subclasses to create        specialized LogRecords.        """"""声明LogRecord对象"""        rv = LogRecord(name, level, fn, lno, msg, args, exc_info, func)        if extra is not None:  # 通过extra属性，可以为LogRecord对象添加未定义的属性，结合LoggerAdapter类和Formatter类，可以实现在日志文本中使用自定义的内容（s = self._fmt % record.__dict__）            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    def _log(self, level, msg, args, exc_info=None, extra=None):        """        Low-level logging routine which creates a LogRecord and then calls        all the handlers of this logger to handle the record.        """"""收集信息，声明LogRecord实例，调用输出处理函数"""        if _srcfile:  # _srcfile不存在的话，findCaller()函数的功能无法完成            #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 = self.findCaller()            except ValueError:                fn, lno, func = "(unknown file)", 0, "(unknown function)"        else:            fn, lno, func = "(unknown file)", 0, "(unknown function)"        if exc_info:  # 通过将exc_info设置为一个布尔真的值，可以输出上一个异常的函数调用信息            if not isinstance(exc_info, tuple):                exc_info = sys.exc_info()        record = self.makeRecord(self.name, level, fn, lno, msg, args, exc_info, func, extra)        self.handle(record)    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.        """"""日志能够输出的第二个过滤条件：Logger实例是否允许输出日志；是否满足Logger实例的过滤条件"""        if (not self.disabled) and self.filter(record):            self.callHandlers(record)    def addHandler(self, hdlr):        """        Add the specified handler to this logger.        """        _acquireLock()        try:            if not (hdlr in self.handlers):                self.handlers.append(hdlr)        finally:            _releaseLock()    def removeHandler(self, hdlr):        """        Remove the specified handler from this logger.        """        _acquireLock()        try:            if hdlr in self.handlers:                self.handlers.remove(hdlr)        finally:            _releaseLock()    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.        """"""在允许的范围内（bool(propagate)==True），递归的获取当前Logger实例及上层Logger实例的handler，并分别调用handler进行输出。没有可用handler，视条件决定是否输出错误日志并记录日志能够输出的第三个过滤条件：日志级别是否高于handler级别"""        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) and raiseExceptions and not self.manager.emittedNoHandlerWarning:  # 只要曾经有logger存在无可用handler的问题，之后再出现就不会再输出错误了，因为 and not self.manager.emittedNoHandlerWarning            sys.stderr.write("No handlers could be found for logger"                             " \"%s\"\n" % self.name)            self.manager.emittedNoHandlerWarning = 1    def getEffectiveLevel(self):        """        Get the effective level for this logger.        Loop through this logger and its parents in the logger hierarchy,        looking for a non-zero logging level. Return the first one found.""""""获取当前Logger实例的级别（向上继承），默认设置为notice（Manager实例根节点级别为Warning）        """        logger = self        while logger:            if logger.level:                return logger.level            logger = logger.parent        return NOTSET    def isEnabledFor(self, level):        """        Is this logger enabled for level 'level'?""""""根据日志等级判断是否允许输出，包含两方面的判断：1、高于manager设置的日志级别下限；高于logger的级别2、级别小于当前logger级别的不允许输出，logger的级别由Logger.level属性决定，若未设置就根据层次结构向上查询，查到位置，注意，Logger默认设置日志级别为notice影响日志能否输出的第一层过滤        """        if self.manager.disable >= level:            return 0        return level >= self.getEffectiveLevel()    def getChild(self, suffix):        """        Get a logger which is a descendant to this one.        This is a convenience method, such that        logging.getLogger('abc').getChild('def.ghi')        is the same as        logging.getLogger('abc.def.ghi')        It's useful, for example, when the parent logger is named using        __name__ rather than a literal string.""""""通过指定后缀，返回当前logger节点的子节点        """        if self.root is not self:            suffix = '.'.join((self.name, suffix))        return self.manager.getLogger(suffix)class RootLogger(Logger):    """    A root logger is not that different to any other logger, except that    it must have a logging level and there is only one instance of it in    the hierarchy.    """    def __init__(self, level):        """        Initialize the logger with the name "root".        """        Logger.__init__(self, "root", level)_loggerClass = Loggerclass LoggerAdapter(object):    """    An adapter for loggers which makes it easier to specify contextual    information in logging output.""""""对Logger实例再进行一次封装。为该Logger实例创建的LogRecord实例提供额外属性。可以结合Fomatter类将额外提供的属性输出为最终日志。    """    def __init__(self, logger, extra):        """        Initialize the adapter with a logger and a dict-like object which        provides contextual information. This constructor signature allows        easy stacking of LoggerAdapters, if so desired.        You can effectively pass keyword arguments as shown in the        following example:        adapter = LoggerAdapter(someLogger, dict(p1=v1, p2="v2"))        """        self.logger = logger        self.extra = extra    def process(self, msg, kwargs):        """        Process the logging message and keyword arguments passed in to        a logging call to insert contextual information. You can either        manipulate the message itself, the keyword args or both. Return        the message and kwargs modified (or not) to suit your needs.        Normally, you'll only need to override this one method in a        LoggerAdapter subclass for your specific needs.        """        kwargs["extra"] = self.extra        return msg, kwargs    def debug(self, msg, *args, **kwargs):        """        Delegate a debug call to the underlying logger, after adding        contextual information from this adapter instance.        """        msg, kwargs = self.process(msg, kwargs)        self.logger.debug(msg, *args, **kwargs)    def info(self, msg, *args, **kwargs):        """        Delegate an info call to the underlying logger, after adding        contextual information from this adapter instance.        """        msg, kwargs = self.process(msg, kwargs)        self.logger.info(msg, *args, **kwargs)    def warning(self, msg, *args, **kwargs):        """        Delegate a warning call to the underlying logger, after adding        contextual information from this adapter instance.        """        msg, kwargs = self.process(msg, kwargs)        self.logger.warning(msg, *args, **kwargs)    def error(self, msg, *args, **kwargs):        """        Delegate an error call to the underlying logger, after adding        contextual information from this adapter instance.        """        msg, kwargs = self.process(msg, kwargs)        self.logger.error(msg, *args, **kwargs)    def exception(self, msg, *args, **kwargs):        """        Delegate an exception call to the underlying logger, after adding        contextual information from this adapter instance.        """        msg, kwargs = self.process(msg, kwargs)        kwargs["exc_info"] = 1        self.logger.error(msg, *args, **kwargs)    def critical(self, msg, *args, **kwargs):        """        Delegate a critical call to the underlying logger, after adding        contextual information from this adapter instance.        """        msg, kwargs = self.process(msg, kwargs)        self.logger.critical(msg, *args, **kwargs)    def log(self, level, msg, *args, **kwargs):        """        Delegate a log call to the underlying logger, after adding        contextual information from this adapter instance.        """        msg, kwargs = self.process(msg, kwargs)        self.logger.log(level, msg, *args, **kwargs)    def isEnabledFor(self, level):        """        See if the underlying logger is enabled for the specified level.        """        return self.logger.isEnabledFor(level)root = RootLogger(WARNING)# 为Logger类添加一个类属性Logger.root = rootLogger.manager = Manager(Logger.root)#---------------------------------------------------------------------------# Configuration classes and functions#---------------------------------------------------------------------------BASIC_FORMAT = "%(levelname)s:%(name)s:%(message)s"def basicConfig(**kwargs):    """    Do basic configuration for the logging system.    This function does nothing if the root logger already has handlers    configured. It is a convenience method intended for use by simple scripts    to do one-shot configuration of the logging package.    The default behaviour is to create a StreamHandler which writes to    sys.stderr, set a formatter using the BASIC_FORMAT format string, and    add the handler to the root logger.    A number of optional keyword arguments may be specified, which can alter    the default behaviour.    filename  Specifies that a FileHandler be created, using the specified              filename, rather than a StreamHandler.    filemode  Specifies the mode to open the file, if filename is specified              (if filemode is unspecified, it defaults to 'a').    format    Use the specified format string for the handler.    datefmt   Use the specified date/time format.    level     Set the root logger level to the specified level.    stream    Use the specified stream to initialize the StreamHandler. Note              that this argument is incompatible with 'filename' - if both              are present, 'stream' is ignored.    Note that you could specify a stream created using open(filename, mode)    rather than passing the filename and mode in. However, it should be    remembered that StreamHandler does not close its stream (since it may be    using sys.stdout or sys.stderr), whereas FileHandler closes its stream    when the handler is closed.    """"""配置根节点"""    # Add thread safety in case someone mistakenly calls    # basicConfig() from multiple threads    _acquireLock()    try:        if len(root.handlers) == 0:            filename = kwargs.get("filename")            if filename:                mode = kwargs.get("filemode", 'a')                hdlr = FileHandler(filename, mode)            else:                stream = kwargs.get("stream")                hdlr = StreamHandler(stream)            fs = kwargs.get("format", BASIC_FORMAT)            dfs = kwargs.get("datefmt", None)            fmt = Formatter(fs, dfs)            hdlr.setFormatter(fmt)            root.addHandler(hdlr)            level = kwargs.get("level")            if level is not None:                root.setLevel(level)    finally:        _releaseLock()#---------------------------------------------------------------------------# Utility functions at module level.# Basically delegate everything to the root logger.#---------------------------------------------------------------------------def getLogger(name=None):    """    Return a logger with the specified name, creating it if necessary.    If no name is specified, return the root logger.""""""用户获取Logger实例的接口方法    """    if name:        return Logger.manager.getLogger(name)    else:        return root#def getRootLogger():#    """#    Return the root logger.##    Note that getLogger('') now does the same thing, so this function is#    deprecated and may disappear in the future.#    """#    return root# 提供了一组函数简便的使用logging模块（基于根节点）def critical(msg, *args, **kwargs):    """    Log a message with severity 'CRITICAL' on the root logger.    """    if len(root.handlers) == 0:        basicConfig()    root.critical(msg, *args, **kwargs)fatal = criticaldef error(msg, *args, **kwargs):    """    Log a message with severity 'ERROR' on the root logger.    """    if len(root.handlers) == 0:        basicConfig()    root.error(msg, *args, **kwargs)def exception(msg, *args, **kwargs):    """    Log a message with severity 'ERROR' on the root logger,    with exception information.    """    kwargs['exc_info'] = 1    error(msg, *args, **kwargs)def warning(msg, *args, **kwargs):    """    Log a message with severity 'WARNING' on the root logger.    """    if len(root.handlers) == 0:        basicConfig()    root.warning(msg, *args, **kwargs)warn = warningdef info(msg, *args, **kwargs):    """    Log a message with severity 'INFO' on the root logger.    """    if len(root.handlers) == 0:        basicConfig()    root.info(msg, *args, **kwargs)def debug(msg, *args, **kwargs):    """    Log a message with severity 'DEBUG' on the root logger.    """    if len(root.handlers) == 0:        basicConfig()    root.debug(msg, *args, **kwargs)def log(level, msg, *args, **kwargs):    """    Log 'msg % args' with the integer severity 'level' on the root logger.    """    if len(root.handlers) == 0:        basicConfig()    root.log(level, msg, *args, **kwargs)def disable(level):    """    Disable all logging calls of severity 'level' and below.    """    root.manager.disable = leveldef shutdown(handlerList=_handlerList):    """    Perform any cleanup actions in the logging system (e.g. flushing    buffers).    Should be called at application exit.    """"""关闭未被释放的Handler实例。用于程序退出前的清理。"""    for wr in reversed(handlerList[:]):        #errors might occur, for example, if files are locked        #we just ignore them if raiseExceptions is not set        try:            h = wr()            if h:                try:                    h.acquire()                    h.flush()                    h.close()                except (IOError, ValueError):                    # Ignore errors which might be caused                    # because handlers have been closed but                    # references to them are still around at                    # application exit.                    pass                finally:                    h.release()        except:            if raiseExceptions:                raise            #else, swallow#Let's try and shutdown automatically on application exit...import atexitatexit.register(shutdown)  #注册清理函数# Null handlerclass NullHandler(Handler):    """    This handler does nothing. It's intended to be used to avoid the    "No handlers could be found for logger XXX" one-off warning. This is    important for library code, which may contain code to log events. If a user    of the library does not configure logging, the one-off warning might be    produced; to avoid this, the library developer simply needs to instantiate    a NullHandler and add it to the top-level logger of the library module or    package.    """    def handle(self, record):        pass    def emit(self, record):        pass    def createLock(self):        self.lock = None# Warnings integration_warnings_showwarning = Nonedef _showwarning(message, category, filename, lineno, file=None, line=None):    """    Implementation of showwarnings which redirects to logging, which will first    check to see if the file parameter is None. If a file is specified, it will    delegate to the original warnings implementation of showwarning. Otherwise,    it will call warnings.formatwarning and will log the resulting string to a    warnings logger named "py.warnings" with level logging.WARNING.    """    if file is not None:        if _warnings_showwarning is not None:            _warnings_showwarning(message, category, filename, lineno, file, line)    else:        s = warnings.formatwarning(message, category, filename, lineno, line)        logger = getLogger("py.warnings")        if not logger.handlers:            logger.addHandler(NullHandler())        logger.warning("%s", s)def captureWarnings(capture):    """    If capture is true, redirect all warnings to the logging package.    If capture is False, ensure that warnings are not redirected to logging    but to their original destinations.    """    global _warnings_showwarning    if capture:        if _warnings_showwarning is None:            _warnings_showwarning = warnings.showwarning            warnings.showwarning = _showwarning    else:        if _warnings_showwarning is not None:            warnings.showwarning = _warnings_showwarning            _warnings_showwarning = None