# 16.6. `logging` — Logging facility for Python

源代码: Lib/logging/__init__.py

该模块定义了为应用程序和库实现灵活事件记录系统的函数和类。

The key benefit of having the logging API provided by a standard library module is that all Python modules can participate in logging, so your application log can include your own messages integrated with messages from third-party modules.

The module provides a lot of functionality and flexibility. If you are unfamiliar with logging, the best way to get to grips with it is to see the tutorials (see the links on the right).

The basic classes defined by the module, together with their functions, are listed below.

- Loggers expose the interface that application code directly uses.
- Handlers send the log records (created by loggers) to the appropriate destination.
- Filters provide a finer grained facility for determining which log records to output.
- Formatters specify the layout of log records in the final output.

## 16.6.1. Logger Objects

Loggers have the following attributes and methods. Logger对象一般不会直接实例化得到，而是通过模块级别的函数`logging.getLogger(name)`得到。Multiple calls to `getLogger()` with the same name will always return a reference to the same Logger object.

The `name` is potentially a period-separated hierarchical value, like `foo.bar.baz` (though it could also be just plain `foo`, for example). Loggers that are further down in the hierarchical list are children of loggers higher up in the list. 例如，对于给定的一个logger对象 `foo`，其它logger对象`foo.bar`, `foo.bar.baz`, `foo.bam`，它们都是`foo`的子辈。logger对象名字的层级和python包的层级是相似的,并且如果你使用推荐的结构`logging.getLogger(__name__)`来管理你的loggers对象的话，那就与python包的层级结构是一模一样的。因为在一个模块中`__name__`是一个在python包中名字空间的模块的名称。

class `logging.``Logger`

`Logger.``propagate`

  If this evaluates to true, events logged to this logger will be passed to the handlers of higher level (ancestor) loggers, in addition to any handlers attached to this logger. Messages are passed directly to the ancestor loggers’ handlers - neither the level nor filters of the ancestor loggers in question are considered.

  If this evaluates to false, logging messages are not passed to the handlers of ancestor loggers.

  The constructor sets this attribute to `True`.

  Note

  如果将处理程序附加到记录器和其一个或多个祖先，它可能会多次发出相同的记录。In general, you should not need to attach a handler to more than one logger - if you just attach it to the appropriate logger which is highest in the logger hierarchy, then it will see all events logged by all descendant loggers, provided that their propagate setting is left set to `True`. A common scenario is to attach handlers only to the root logger, and to let propagation take care of the rest.

`Logger.``setLevel`(lvl)

  Sets the threshold for this logger to lvl. Logging messages which are less severe than lvl will be ignored. When a logger is created, the level is set to `NOTSET` (which causes all messages to be processed when the logger is the root logger, or delegation to the parent when the logger is a non-root logger). Note that the root logger is created with level `WARNING`.

  The term ‘delegation to the parent’ means that if a logger has a level of NOTSET, its chain of ancestor loggers is traversed until either an ancestor with a level other than NOTSET is found, or the root is reached.

  If an ancestor is found with a level other than NOTSET, then that ancestor’s level is treated as the effective level of the logger where the ancestor search began, and is used to determine how a logging event is handled.

  If the root is reached, and it has a level of NOTSET, then all messages will be processed. Otherwise, the root’s level will be used as the effective level.

  See Logging Levels for a list of levels.

  Changed in version 3.2: The lvl parameter now accepts a string representation of the level such as ‘INFO’ as an alternative to the integer constants such as `INFO`. 然而，注意，级别在内部存储为整数，并且方法例如 `getEffectiveLevel()`和`isEnabledFor()`将返回/期望被传递的整数。

`Logger.``isEnabledFor`(lvl)

  Indicates if a message of severity lvl would be processed by this logger. This method checks first the module-level level set by `logging.disable(lvl)` and then the logger’s effective level as determined by `getEffectiveLevel()`.

`Logger.``getEffectiveLevel`()

  Indicates the effective level for this logger. If a value other than `NOTSET` has been set using `setLevel()`, it is returned. 否则，将向根向前遍历层次结构，直到找到除`NOTSET`之外的值，并返回该值。返回的值是一个整数，通常为`logging.DEBUG`，`logging.INFO`等。

`Logger.``getChild`(suffix)

  Returns a logger which is a descendant to this logger, as determined by the suffix. Thus, `logging.getLogger('abc').getChild('def.ghi')` would return the same logger as would be returned by `logging.getLogger('abc.def.ghi')`. 这是一个方便的方法，当父记录器使用例如`__ name __`而不是字面值字符串。

  版本3.2中的新功能。

`Logger.``debug`(msg, *args, **kwargs)

  Logs a message with level `DEBUG` on this logger. The msg is the message format string, and the args are the arguments which are merged into msg using the string formatting operator. (Note that this means that you can use keywords in the format string, together with a single dictionary argument.)

  在kwargs中有三个关键字参数，它们被检查：exc_info，stack_info和extra。

  如果exc_info不计算为假，则会导致将异常信息添加到日志记录消息中。如果提供了异常元组（以`sys.exc_info()`返回的格式）或异常实例，则使用它；否则，调用`sys.exc_info()`以获取异常信息。

  第二个可选的关键字参数是stack_info，默认为`False`。如果为true，则将堆栈信息添加到日志记录消息中，包括实际的日志调用。注意，这不是通过指定exc_info显示的堆栈信息：前者是从堆栈底部到当前线程中的日志调用的堆栈帧，而后者是有关堆栈帧，它们在寻找异常处理程序时例外之后被解开。

  您可以独立于exc_info指定stack_info，例如只是展示你如何到达代码中的某一点，即使没有引发异常。堆栈帧打印在标题行后面，说：

      Stack (most recent call last):

  This mimics the `Traceback (most recent call last):` which is used when displaying exception frames.

  第三个关键字参数是extra，可用于传递一个字典，用于填充为具有用户定义属性的日志记录事件创建的LogRecord的__dict__。These custom attributes can then be used as you like. For example, they could be incorporated into logged messages. For example:

      FORMAT = '%(asctime)-15s %(clientip)s %(user)-8s %(message)s'
      logging.basicConfig(format=FORMAT)
      d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
      logger = logging.getLogger('tcpserver')
      logger.warning('Protocol problem: %s', 'connection reset', extra=d)

  would print something like

      2006-02-08 22:20:02,165 192.168.0.1 fbloggs  Protocol problem: connection reset

  The keys in the dictionary passed in extra should not clash with the keys used by the logging system. (See the `Formatter` documentation for more information on which keys are used by the logging system.)

  If you choose to use these attributes in logged messages, you need to exercise some care. In the above example, for instance, the `Formatter` has been set up with a format string which expects ‘clientip’ and ‘user’ in the attribute dictionary of the LogRecord. If these are missing, the message will not be logged because a string formatting exception will occur. So in this case, you always need to pass the extra dictionary with these keys.

  While this might be annoying, this feature is intended for use in specialized circumstances, such as multi-threaded servers where the same code executes in many contexts, and interesting conditions which arise are dependent on this context (such as remote client IP address and authenticated user name, in the above example). In such circumstances, it is likely that specialized `Formatter`s would be used with particular `Handler`s.

  New in version 3.2: The stack_info parameter was added.

  Changed in version 3.5: The exc_info parameter can now accept exception instances.

`Logger.``info`(msg, *args, **kwargs)

  Logs a message with level `INFO` on this logger. The arguments are interpreted as for `debug()`.

`Logger.``warning`(msg, *args, **kwargs)

  Logs a message with level `WARNING` on this logger. The arguments are interpreted as for `debug()`.

  Note

  有一个过时的方法`warn`，其功能与`warning`相同。由于`warn`已弃用，请不要使用它 - 请改用`warning`。

`Logger.``error`(msg, *args, **kwargs)

  Logs a message with level `ERROR` on this logger. The arguments are interpreted as for `debug()`.

`Logger.``critical`(msg, *args, **kwargs)

  Logs a message with level `CRITICAL` on this logger. The arguments are interpreted as for `debug()`.

`Logger.``log`(lvl, msg, *args, **kwargs)

  Logs a message with integer level lvl on this logger. The other arguments are interpreted as for `debug()`.

`Logger.``exception`(msg, *args, **kwargs)

  Logs a message with level `ERROR` on this logger. The arguments are interpreted as for `debug()`. Exception info is added to the logging message. This method should only be called from an exception handler.

`Logger.``addFilter`(filt)

  Adds the specified filter filt to this logger.

`Logger.``removeFilter`(filt)

  Removes the specified filter filt from this logger.

`Logger.``filter`(record)

  Applies this logger’s filters to the record and returns a true value if the record is to be processed. The filters are consulted in turn, until one of them returns a false value. If none of them return a false value, the record will be processed (passed to handlers). If one returns a false value, no further processing of the record occurs.

`Logger.``addHandler`(hdlr)

  Adds the specified handler hdlr to this logger.

`Logger.``removeHandler`(hdlr)

  Removes the specified handler hdlr from this logger.

`Logger.``findCaller`(stack_info=False)

  Finds the caller’s source filename and line number. 将文件名，行号，函数名和堆栈信息作为4元素元组返回。除非stack_info为True，否则堆栈信息将作为无返回。

`Logger.``handle`(record)

  Handles a record by passing it to all handlers associated with this logger and its ancestors (until a false value of propagate is found). This method is used for unpickled records received from a socket, as well as those created locally. Logger-level filtering is applied using `filter()`.

`Logger.``makeRecord`(name, lvl, fn, lno, msg, args, exc_info, func=None, extra=None, sinfo=None)

  This is a factory method which can be overridden in subclasses to create specialized `LogRecord` instances.

`Logger.``hasHandlers`()

  检查此记录器是否已配置任何处理程序。这是通过在记录器层次结构中查找此记录器及其父节点中的处理程序来完成的。如果找到处理程序，则返回`True`，否则`False`。当找到具有“propagate”属性设置为False的记录器时，该方法停止搜索层次结构 - 这将是检查处理程序是否存在的最后一个记录器。

  New in version 3.2.

## 16.6.2. Logging Levels

The numeric values of logging levels are given in the following table. These are primarily of interest if you want to define your own levels, and need them to have specific values relative to the predefined levels. 如果定义具有相同数值的级别，它将覆盖预定义值；预定义的名称将丢失。

Level | Numeric value
--- | ---
`CRITICAL` | 50
`ERROR` | 40
`WARNING` | 30
`INFO` | 20
`DEBUG` | 10
`NOTSET` | 0

## 16.6.3. Handler Objects

Handlers have the following attributes and methods. 注意：`Handler`不应该直接被实例化，此类应该作为基类来子类化出一些有用的类。然而，`__init__()`方法在子类中需要被`Handler.__init__()`来调用。

`Handler.``__init__`(level=NOTSET)

  Initializes the `Handler` instance by setting its level, setting the list of filters to the empty list and creating a lock (using `createLock()`) for serializing access to an I/O mechanism.

`Handler.``createLock`()

  Initializes a thread lock which can be used to serialize access to underlying I/O functionality which may not be threadsafe.

`Handler.``acquire`()

  Acquires the thread lock created with `createLock()`.

`Handler.``release`()

  Releases the thread lock acquired with `acquire()`.

`Handler.``setLevel`(lvl)

  Sets the threshold for this handler to lvl. Logging messages which are less severe than lvl will be ignored. When a handler is created, the level is set to `NOTSET` (which causes all messages to be processed).

  See Logging Levels for a list of levels.

  在版本3.2中更改： lvl参数现在接受级别的字符串表示形式，如“INFO”，作为整数常量的替代，如`INFO` 。

`Handler.``setFormatter`(form)

  Sets the `Formatter` for this handler to form.

`Handler.``addFilter`(filt)

  Adds the specified filter filt to this handler.

`Handler.``removeFilter`(filt)

  Removes the specified filter filt from this handler.

`Handler.``filter`(record)

  Applies this handler’s filters to the record and returns a true value if the record is to be processed. The filters are consulted in turn, until one of them returns a false value. If none of them return a false value, the record will be emitted. If one returns a false value, the handler will not emit the record.

`Handler.``flush`()

  Ensure all logging output has been flushed. This version does nothing and is intended to be implemented by subclasses.

`Handler.``close`()

  Tidy up any resources used by the handler. This version does no output but removes the handler from an internal list of handlers which is closed when `shutdown()` is called. Subclasses should ensure that this gets called from overridden `close()` methods.

`Handler.``handle`(record)

  Conditionally emits the specified logging record, depending on filters which may have been added to the handler. Wraps the actual emission of the record with acquisition/release of the I/O thread lock.

`Handler.``handleError`(record)

  此方法应该在调用`emit()`时遇到异常后从handlers被调用。If the module-level attribute `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 specified record is the one which was being processed when the exception occurred. (The default value of `raiseExceptions` is `True`, as that is more useful during development).

`Handler.``format`(record)

  Do formatting for a record - if a formatter is set, use it. Otherwise, use the default formatter for the module.

`Handler.``emit`(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`.

For a list of handlers included as standard, see `logging.handlers`.

## 16.6.4. Formatter Objects

`Formatter`对象有以下属性和方法。它负责将`LogRecord`转换（通常）成人类和其它系统可以理解的字符串。基类`Formatter`允许指定某个格式的字符串。如果提供None，那么`'%(message)s'`将会作为默认值，它仅仅包括日志调用中的信息。如果想加入一些额外的格式输出（例如时间戳）信息项，请继续阅读下去。

Formatter对象可以用一个使`LogRecord`的属性的反应信息有用的字符串来进行实例化。例如上面提到的用来使用户信息和参数预格式化进`LogRecord`对象的 message属性有效的默认值。This format string contains standard Python %-style mapping keys. 欲了解更多关于字符串格式化的信息，请参见printf-style String Formatting。

在`LogRecord`对象中，有效的映射键存在于LogRecord attributes属性中。

class `logging.``Formatter`(fmt=None, datefmt=None, style='%')

  返回一个`Formatter`类的新实例。The instance is initialized with a format string for the message as a whole, as well as a format string for the date/time portion of a message. 如果fmt不被指定, `'%(message)s'`将会被使用。If no datefmt is specified, the ISO8601 date format is used.

  style可以是 ‘%’, ‘{‘ or ‘$’中的任何一个，并且它决定格式化字符串将会怎样与它的数据融合: 使用%格式化的更多信息参考`str.format()` or `string.Template`.有关使用{ - 和$ - 格式化日志消息的详细信息，请参阅在应用程序中使用特定格式样式。

  在版本3.2中已更改：添加了样式参数。

  `format`(record)

    The record’s attribute dictionary is used as the operand to a string formatting operation. Returns the resulting string. Before formatting the dictionary, a couple of preparatory steps are carried out. The message attribute of the record is computed using msg % args. If the formatting string contains `'(asctime)'`, `formatTime()` is called to format the event time. If there is exception information, it is formatted using `formatException()` and appended to the message. Note that the formatted exception information is cached in attribute exc_text. This is useful because the exception information can be pickled and sent across the wire, but you should be careful if you have more than one `Formatter` subclass which customizes the formatting of exception information. In this case, you will have to clear the cached value after a formatter has done its formatting, so that the next formatter to handle the event doesn’t use the cached value but recalculates it afresh.

    If stack information is available, it’s appended after the exception information, using `formatStack()` to transform it if necessary.

  `formatTime`(record, datefmt=None)

    此方法应该被从想使用格式化时间的formatter对象的`format()`调用。This method can be overridden in formatters to provide for any specific requirement, but the basic behavior 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. 默认情况下，使用`time.localtime()`；为特定格式化程序更改此属性实例，将`转换器`属性设置为具有与`time.localtime()`或`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.

    在版本3.3中更改：以前，默认的ISO 8601格式是硬编码的，如在此示例中：`2010-09-06 22:38： 15,292`其中逗号之前的部分由strptime格式字符串处理（`'％Y-％m-％d ％H：％M ：％S'`），逗号后面的部分是毫秒值。因为strptime没有毫秒的格式占位符，所以使用另一个格式字符串`'％s，％03d'`附加毫秒值，并且这两个格式字符串都已硬编码到此方法中。随着改变，这些字符串被定义为类级别的属性，在需要时可以在实例级别被覆盖。属性的名称为`default_time_format`（对于strptime格式字符串）和`default_msec_format`（用于追加毫秒值）。

  `formatException`(exc_info)

    Formats the specified exception information (a standard exception tuple as returned by `sys.exc_info()`) as a string. This default implementation just uses `traceback.print_exception()`. The resulting string is returned.

  `formatStack`(stack_info)

    格式化指定的堆栈信息（由`traceback.print_stack()`返回的字符串，但删除了最后一个换行符）作为字符串。这个默认实现只返回输入值。

## 16.6.5. Filter Objects

`Filters` can be used by `Handlers` and `Loggers` for more sophisticated filtering than is provided by levels. The base filter class only allows events which are below a certain point in the logger hierarchy. 例如，用“A.B”初始化的过滤器将允许由记录器“A.B”，“A.B.C”，“A.B.C.D”，“A.B.D”等记录的事件。但是,不接受“A.BB”，“B.A.B”等的格式。If initialized with the empty string, all events are passed.

class `logging.``Filter`(name='')

  Returns an instance of the `Filter` class. If name is specified, it names a logger which, together with its children, will have its events allowed through the filter. If name is the empty string, allows every event.

  `filter`(record)

    Is the specified record to be logged? Returns zero for no, nonzero for yes. If deemed appropriate, the record may be modified in-place by this method.

注意，在处理程序发出事件之前，请参考处理程序附带的过滤器，而记录事件时会查询附加到日志记录器的过滤器（使用`debug()`，`info` 等。), before sending an event to handlers. This means that events which have been generated by descendant loggers will not be filtered by a logger’s filter setting, unless the filter has also been applied to those descendant loggers.

You don’t actually need to subclass `Filter`: you can pass any instance which has a `filter` method with the same semantics.

Changed in version 3.2: You don’t need to create specialized `Filter` classes, or use other classes with a `filter` method: you can use a function (or other callable) as a filter. The filtering logic will check to see if the filter object has a `filter` attribute: if it does, it’s assumed to be a `Filter` and its `filter()` method is called. Otherwise, it’s assumed to be a callable and called with the record as the single parameter. The returned value should conform to that returned by `filter()`.

Although filters are used primarily to filter records based on more sophisticated criteria than levels, they get to see every record which is processed by the handler or logger they’re attached to: this can be useful if you want to do things like counting how many records were processed by a particular logger or handler, or adding, changing or removing attributes in the LogRecord being processed. Obviously changing the LogRecord needs to be done with some care, but it does allow the injection of contextual information into logs (see Using Filters to impart contextual information).

## 16.6.6. LogRecord Objects

每次某个事件被日志记录时`LogRecord`实例就会被`Logger`自动创建，并且可以被手动创建，通过 `makeLogRecord()` (例如，一个网络序列化事件).

class `logging.``LogRecord`(name, level, pathname, lineno, msg, args, exc_info, func=None, sinfo=None)

  Contains all the information pertinent to the event being logged.

  主要信息由`msg`和`args`传入，which are combined using `msg % args` to create the `message` field of the record.

  Parameters: | name - 用于记录由此LogRecord表示的事件的记录器的名称。Note that this name will always have this value, even though it may be emitted by a handler attached to a different (ancestor) logger. level - 记录事件的数字级别（DEBUG，INFO等之一）请注意，将其转换为LogRecord的两个属性：`levelno`表示数字值，`levelname`表示相应的级别名称。 pathname - 进行记录调用的源文件的完整路径名。 lineno - 进行日志调用的源文件中的行号。 msg - 事件描述消息，可能是带有变量数据占位符的格式字符串。 args - 要合并到msg参数中的变量数据，以获取事件描述。 exc_info - 当前异常信息的异常元组，如果没有异常信息，则为None。 func - 调用日志记录调用的函数或方法的名称。 sinfo - 表示当前线程中堆栈基址的堆栈信息的文本字符串，直到日志调用。

  `getMessage`()

    `LogRecord`实例在融合用户提供的参数后返回一条message。If the user-supplied message argument to the logging call is not a string, `str()` is called on it to convert it to a string. This allows use of user-defined classes as messages, whose `__str__` method can return the actual format string to be used.

  在版本3.2中已更改：通过提供用于创建记录的工厂，可以更轻松地创建`LogRecord`。可以使用`getLogRecordFactory()`和`setLogRecordFactory()`来设置工厂（参见工厂的签名）。

  此功能可用于在创建时将自己的值注入LogRecord。您可以使用以下模式：

      old_factory = logging.getLogRecordFactory()

      def record_factory(*args, **kwargs):
          record = old_factory(*args, **kwargs)
          record.custom_attribute = 0xdecafbad
          return record

      logging.setLogRecordFactory(record_factory)

  使用这种模式，多个工厂可以链接，并且只要它们不会覆盖彼此的属性或无意地覆盖上面列出的标准属性，就不会有任何意外。

## 16.6.7. LogRecord attributes

The LogRecord has a number of attributes, most of which are derived from the parameters to the constructor. (Note that the names do not always correspond exactly between the LogRecord constructor parameters and the LogRecord attributes.) These attributes can be used to merge data from the record into the format string. The following table lists (in alphabetical order) the attribute names, their meanings and the corresponding placeholder in a %-style format string.

如果使用{} -formatting（`str.format()`），则可以使用`{attrname}`作为格式字符串中的占位符。如果您使用$ -formatting（`string.Template`），请使用形式`$ {attrname}`。在这两种情况下，当然，将`attrname`替换为要使用的实际属性名称。

在{}格式化的情况下，您可以通过将属性名称放在属性名称后面指定格式化标记，并用冒号分隔。例如：`{msecs：03d}`的占位符会将`4`的毫秒值格式化为`004`。有关可用选项的完整详细信息，请参阅`str.format()`文档。

Attribute name | Format | Description
--- | --- | ---
args | You shouldn’t need to format this yourself. | The tuple of arguments merged into `msg` to produce `message`, or a dict whose values are used for the merge (when there is only one argument, and it is a dictionary).
asctime | `%(asctime)s` | Human-readable time when the `LogRecord` was created. By default this is of the form ‘2003-07-08 16:49:45,896’ (the numbers after the comma are millisecond portion of the time).
created | `%(created)f` | Time when the `LogRecord` was created (as returned by `time.time()`).
exc_info | You shouldn’t need to format this yourself. | Exception tuple (à la `sys.exc_info`) or, if no exception has occurred, None.
filename | `%(filename)s` | Filename portion of `pathname`.
funcName | `%(funcName)s` | Name of function containing the logging call.
levelname | `%(levelname)s` | Text logging level for the message (`'DEBUG'`, `'INFO'`, `'WARNING'`, `'ERROR'`, `'CRITICAL'`).
levelno | `%(levelno)s` | Numeric logging level for the message (`DEBUG`, `INFO`, `WARNING`, `ERROR`, `CRITICAL`).
行号 | `%(lineno)d` | Source line number where the logging call was issued (if available).
module | `%(module)s` | Module (name portion of `filename`).
msecs | `%(msecs)d` | Millisecond portion of the time when the `LogRecord` was created.
message | `%(message)s` | The logged message, computed as `msg % args`. This is set when `Formatter.format()` is invoked.
msg | You shouldn’t need to format this yourself. | The format string passed in the original logging call. Merged with `args` to produce `message`, or an arbitrary object (see Using arbitrary objects as messages).
name | `%(name)s` | Name of the logger used to log the call.
pathname | `%(pathname)s` | Full pathname of the source file where the logging call was issued (if available).
process | `%(process)d` | Process ID (if available).
processName | `%(processName)s` | Process name (if available).
relativeCreated | `%(relativeCreated)d` | Time in milliseconds when the LogRecord was created, relative to the time the logging module was loaded.
stack_info | You shouldn’t need to format this yourself. | Stack frame information (where available) from the bottom of the stack in the current thread, up to and including the stack frame of the logging call which resulted in the creation of this record.
thread | `%(thread)d` | Thread ID (if available).
threadName | `%(threadName)s` | Thread name (if available).

Changed in version 3.1: processName was added.

## 16.6.8. LoggerAdapter Objects

`LoggerAdapter`实例用来方便的传递文本信息给logging调用。For a usage example, see the section on adding contextual information to your logging output.

class `logging.``LoggerAdapter`(logger, extra)

  Returns an instance of `LoggerAdapter` initialized with an underlying `Logger` instance and a dict-like object.

  `process`(msg, kwargs)

    Modifies the message and/or keyword arguments passed to a logging call in order to insert contextual information. This implementation takes the object passed as extra to the constructor and adds it to kwargs using key ‘extra’. The return value is a (msg, kwargs) tuple which has the (possibly modified) versions of the arguments passed in.

In addition to the above, `LoggerAdapter` supports the following methods of `Logger`: `debug()`, `info()`, `warning()`, `error()`, `exception()`, `critical()`, `log()`, `isEnabledFor()`, `getEffectiveLevel()`, `setLevel()` and `hasHandlers()`. These methods have the same signatures as their counterparts in `Logger`, so you can use the two types of instances interchangeably.

Changed in version 3.2: The `isEnabledFor()`, `getEffectiveLevel()`, `setLevel()` and `hasHandlers()` methods were added to `LoggerAdapter`. These methods delegate to the underlying logger.

## 16.6.9. Thread Safety

The logging module is intended to be thread-safe without any special work needing to be done by its clients. 它实现了这一点，虽然使用线程锁；有一个锁来串行访问模块的共享数据，并且每个处理程序还创建一个锁以串行化对其底层I / O的访问。

If you are implementing asynchronous signal handlers using the `signal` module, you may not be able to use logging from within such handlers. This is because lock implementations in the `threading` module are not always re-entrant, and so cannot be invoked from such signal handlers.

## 16.6.10. Module-Level Functions

In addition to the classes described above, there are a number of module- level functions.

`logging.``getLogger`(name=None)

  返回具有指定名称的记录器，如果名称为`无`，则返回一个记录器，它是层次结构的根记录器。如果指定，名称通常是点分隔的分层名称，如'a'，'a.b'或'a.b.c.d'。Choice of these names is entirely up to the developer who is using logging.

  All calls to this function with a given name return the same logger instance. This means that logger instances never need to be passed between different parts of an application.

`logging.``getLoggerClass`()

  Return either the standard `Logger` class, or the last class passed to `setLoggerClass()`. This function may be called from within a new class definition, to ensure that installing a customized `Logger` class will not undo customizations already applied by other code. For example:

      class MyLogger(logging.getLoggerClass()):
          # ... override behaviour here

`logging.``getLogRecordFactory`()

  Return a callable which is used to create a `LogRecord`.

  New in version 3.2: This function has been provided, along with `setLogRecordFactory()`, to allow developers more control over how the `LogRecord` representing a logging event is constructed.

  See `setLogRecordFactory()` for more information about the how the factory is called.

`logging.``debug`(msg, *args, **kwargs)

  Logs a message with level `DEBUG` on the root logger. The msg is the message format string, and the args are the arguments which are merged into msg using the string formatting operator. (Note that this means that you can use keywords in the format string, together with a single dictionary argument.)

  There are three keyword arguments in kwargs which are inspected: exc_info which, if it does not evaluate as false, causes exception information to be added to the logging message. If an exception tuple (in the format returned by `sys.exc_info()`) is provided, it is used; otherwise, `sys.exc_info()` is called to get the exception information.

  The second optional keyword argument is stack_info, which defaults to `False`. If true, stack information is added to the logging message, including the actual logging call. Note that this is not the same stack information as that displayed through specifying exc_info: The former is stack frames from the bottom of the stack up to the logging call in the current thread, whereas the latter is information about stack frames which have been unwound, following an exception, while searching for exception handlers.

  You can specify stack_info independently of exc_info, e.g. to just show how you got to a certain point in your code, even when no exceptions were raised. The stack frames are printed following a header line which says:

      Stack (most recent call last):

  This mimics the `Traceback (most recent call last):` which is used when displaying exception frames.

  The third optional keyword argument is extra which can be used to pass a dictionary which is used to populate the __dict__ of the LogRecord created for the logging event with user-defined attributes. These custom attributes can then be used as you like. For example, they could be incorporated into logged messages. For example:

      FORMAT = '%(asctime)-15s %(clientip)s %(user)-8s %(message)s'
      logging.basicConfig(format=FORMAT)
      d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
      logging.warning('Protocol problem: %s', 'connection reset', extra=d)

  would print something like:

      2006-02-08 22:20:02,165 192.168.0.1 fbloggs  Protocol problem: connection reset

  The keys in the dictionary passed in extra should not clash with the keys used by the logging system. (See the `Formatter` documentation for more information on which keys are used by the logging system.)

  If you choose to use these attributes in logged messages, you need to exercise some care. In the above example, for instance, the `Formatter` has been set up with a format string which expects ‘clientip’ and ‘user’ in the attribute dictionary of the LogRecord. If these are missing, the message will not be logged because a string formatting exception will occur. So in this case, you always need to pass the extra dictionary with these keys.

  While this might be annoying, this feature is intended for use in specialized circumstances, such as multi-threaded servers where the same code executes in many contexts, and interesting conditions which arise are dependent on this context (such as remote client IP address and authenticated user name, in the above example). In such circumstances, it is likely that specialized `Formatter`s would be used with particular `Handler`s.

  New in version 3.2: The stack_info parameter was added.

`logging.``info`(msg, *args, **kwargs)

  Logs a message with level `INFO` on the root logger. The arguments are interpreted as for `debug()`.

`logging.``warning`(msg, *args, **kwargs)

  Logs a message with level `WARNING` on the root logger. The arguments are interpreted as for `debug()`.

  Note

  There is an obsolete function `warn` which is functionally identical to `warning`. As `warn` is deprecated, please do not use it - use `warning` instead.

`logging.``error`(msg, *args, **kwargs)

  Logs a message with level `ERROR` on the root logger. The arguments are interpreted as for `debug()`.

`logging.``critical`(msg, *args, **kwargs)

  Logs a message with level `CRITICAL` on the root logger. The arguments are interpreted as for `debug()`.

`logging.``exception`(msg, *args, **kwargs)

  Logs a message with level `ERROR` on the root logger. The arguments are interpreted as for `debug()`. Exception info is added to the logging message. This function should only be called from an exception handler.

`logging.``log`(level, msg, *args, **kwargs)

  Logs a message with level level on the root logger. The other arguments are interpreted as for `debug()`.

  Note

  The above module-level convenience functions, which delegate to the root logger, call `basicConfig()` to ensure that at least one handler is available. Because of this, they should not be used in threads, in versions of Python earlier than 2.7.1 and 3.2, unless at least one handler has been added to the root logger before the threads are started. In earlier versions of Python, due to a thread safety shortcoming in `basicConfig()`, this can (under rare circumstances) lead to handlers being added multiple times to the root logger, which can in turn lead to multiple messages for the same event.

`logging.``disable`(lvl)

  Provides an overriding level lvl for all loggers which takes precedence over the logger’s own level. When the need arises to temporarily throttle logging output down across the whole application, this function can be useful. Its effect is to disable all logging calls of severity lvl and below, so that if you call it with a value of INFO, then all INFO and DEBUG events would be discarded, whereas those of severity WARNING and above would be processed according to the logger’s effective level. If `logging.disable(logging.NOTSET)` is called, it effectively removes this overriding level, so that logging output again depends on the effective levels of individual loggers.

`logging.``addLevelName`(lvl, levelName)

  Associates level lvl with text levelName in an internal dictionary, which is used to map numeric levels to a textual representation, for example when a `Formatter` formats a message. This function can also be used to define your own levels. The only constraints are that all levels used must be registered using this function, levels should be positive integers and they should increase in increasing order of severity.

  Note

  If you are thinking of defining your own levels, please see the section on Custom Levels.

`logging.``getLevelName`(lvl)

  Returns the textual representation of logging level lvl. If the level is one of the predefined levels `CRITICAL`, `ERROR`, `WARNING`, `INFO` or `DEBUG` then you get the corresponding string. If you have associated levels with names using `addLevelName()` then the name you have associated with lvl 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’ % lvl is returned.

  Note

  Levels are internally integers (as they need to be compared in the logging logic). This function is used to convert between an integer level and the level name displayed in the formatted log output by means of the `%(levelname)s` format specifier (see LogRecord attributes).

  Changed in version 3.4: In Python versions earlier than 3.4, this function could also be passed a text level, and would return the corresponding numeric value of the level. This undocumented behaviour was considered a mistake, and was removed in Python 3.4, but reinstated in 3.4.2 due to retain backward compatibility.

`logging.``makeLogRecord`(attrdict)

  Creates and returns a new `LogRecord` instance whose attributes are defined by attrdict. This function is useful for taking a pickled `LogRecord` attribute dictionary, sent over a socket, and reconstituting it as a `LogRecord` instance at the receiving end.

`logging.``basicConfig`(**kwargs)

  Does basic configuration for the logging system by creating a `StreamHandler` with a default `Formatter` and adding it to the root logger. The functions `debug()`, `info()`, `warning()`, `error()` and `critical()` will call `basicConfig()` automatically if no handlers are defined for the root logger.

  This function does nothing if the root logger already has handlers configured for it.

  Note

  This function should be called from the main thread before other threads are started. In versions of Python prior to 2.7.1 and 3.2, if this function is called from multiple threads, it is possible (in rare circumstances) that a handler will be added to the root logger more than once, leading to unexpected results such as messages being duplicated in the log.

  The following keyword arguments are supported.

  Format | Description
  --- | ---
  `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.
  `style` | If `format` is specified, use this style for the format string. One of ‘%’, ‘{‘ or ‘$’ for %-formatting, `str.format()` or `string.Template` respectively, and defaulting to ‘%’ if not specified.
  `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, a `ValueError` is raised.
  `handlers` | If specified, this should be an iterable of already created handlers to add to the root logger. Any handlers which don’t already have a formatter set will be assigned the default formatter created in this function. Note that this argument is incompatible with ‘filename’ or ‘stream’ - if both are present, a `ValueError` is raised.

  Changed in version 3.2: The `style` argument was added.

  Changed in version 3.3: The `handlers` argument was added. Additional checks were added to catch situations where incompatible arguments are specified (e.g. `handlers` together with `stream` or `filename`, or `stream` together with `filename`).

`logging.``shutdown`()

  Informs the logging system to perform an orderly shutdown by flushing and closing all handlers. This should be called at application exit and no further use of the logging system should be made after this call.

`logging.``setLoggerClass`(klass)

  Tells the logging system to use the class klass when instantiating a logger. The class should define `__init__()` such that only a name argument is required, and the `__init__()` should call `Logger.__init__()`. This function is typically called before any loggers are instantiated by applications which need to use custom logger behavior.

`logging.``setLogRecordFactory`(factory)

  Set a callable which is used to create a `LogRecord`.

  Parameters: | factory – The factory callable to be used to instantiate a log record.

  New in version 3.2: This function has been provided, along with `getLogRecordFactory()`, to allow developers more control over how the `LogRecord` representing a logging event is constructed.

  The factory has the following signature:

  `factory(name, level, fn, lno, msg, args, exc_info, func=None, sinfo=None, **kwargs)`

  > name: | The logger name.
  > level: | The logging level (numeric).
  > fn: | The full pathname of the file where the logging call was made.
  > lno: | The line number in the file where the logging call was made.
  > msg: | The logging message.
  > args: | The arguments for the logging message.
  > exc_info: | An exception tuple, or None.
  > func: | The name of the function or method which invoked the logging call.
  > sinfo: | A stack traceback such as is provided by `traceback.print_stack()`, showing the call hierarchy.
  > kwargs: | Additional keyword arguments.

## 16.6.11. Module-Level Attributes

`logging.``lastResort`

  A “handler of last resort” is available through this attribute. This is a `StreamHandler` writing to `sys.stderr` with a level of `WARNING`, and is used to handle logging events in the absence of any logging configuration. The end result is to just print the message to `sys.stderr`. This replaces the earlier error message saying that “no handlers could be found for logger XYZ”. If you need the earlier behaviour for some reason, `lastResort` can be set to `None`.

  New in version 3.2.

## 16.6.12. Integration with the warnings module

The `captureWarnings()` function can be used to integrate `logging` with the `warnings` module.

`logging.``captureWarnings`(capture)

  This function is used to turn the capture of warnings by logging on and off.

  If capture is `True`, warnings issued by the `warnings` module will be redirected to the logging system. Specifically, a warning will be formatted using `warnings.formatwarning()` and the resulting string logged to a logger named `'py.warnings'` with a severity of `WARNING`.

  If capture is `False`, the redirection of warnings to the logging system will stop, and warnings will be redirected to their original destinations (i.e. those in effect before `captureWarnings(True)` was called).

See also

Module `logging.config`
  Configuration API for the logging module.
Module `logging.handlers`
  Useful handlers included with the logging module.
PEP 282 - A Logging System
  The proposal which described this feature for inclusion in the Python standard library.
Original Python logging package
  This is the original source for the `logging` package. 该站点此版本的包适用与Python 1.5.2, 2.1.x 和 2.2.x，在这些版本的Python标准库中并不包括`logging`包。