學習 python logging（2）: 格式化日誌輸出

1. 簡介

在實際項目中，我們可能需要根據實際需要去記錄日誌，包括記錄的時間、進程號、日誌的等級、出現的對應文件及行號等等，以幫助我們定位問題，分析過程。python已經爲我們提供了基礎的這些，包括:

name	format_str	meaning
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
created	%(created)f	Time when the LogRecord was created (as returned by time.time()).
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).
lineno	%(lineno)d	Source line number where the logging call was issued (if available).
message	%(message)s	The logged message, computed as msg % args. This is set when Formatter.format() is invoked.
module	%(module)s	Module (name portion of filename).
msecs	%(msecs)d	Millisecond portion of the time when the LogRecord was created.
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.
thread	%(thread)d	Thread ID (if available).
threadName	%(threadName)s	Thread name (if available).

在基本使用中，已經足夠了, 簡單的例子:

logging.basicConfig(
    format="%(asctime)s-%(filename)s-%(levelno)s-%(lineno)s, %(message)s"
)
logging.warning("test message")

日誌輸出爲：
2019-01-03 21:36:53,772-logging_format_sample.py-30-11, test message

2. 三種格式化方式

在python中日誌模塊中，有三種格式化日誌信息的方式: %-formatting, str.format(), Template, %s是默認的。

2.1 默認 %-formatting

以上例子已給出

2.2 使用 str.format()

需要將格式化的 style 參數設置成 {。

logging.basicConfig(
    style='{',
    format="{asctime}-{filename}-{levelno}-{lineno}, {message}"
)
logging.warning("test format message")

日誌輸出爲
2019-01-03 21:49:59,689-logging_format_sample.py-30-11, test format message

2.3 使用Template

需要將格式化的 style 參數設置成 $。

logging.basicConfig(
    style='$',
    format="$asctime-$filename-$levelno-$lineno, $message"
)
logging.warning("test template message")

日誌輸出爲
2019-01-03 21:53:56,873-logging_format_sample.py-30-11, test template message

以上，就是記錄日誌格式化消息的基本操作。

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參考:

1. https://docs.python.org/3/howto/logging.html#logging-basic-tutorial
2. https://docs.python.org/3/library/logging.html
3. https://docs.python.org/3/howto/logging-cookbook.html#logging-cookbook