Python logging日志模块的概念与实践讲解

print("This is some information.")

import logging
# Create a logger and set the log level to INFO
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
# Add a StreamHandler to send log messages to console
console_handler = logging.StreamHandler()
logger.addHandler(console_handler)
# Log an informational message
logger.info("This is an informational message.")

import logging
# This will log the message to the console
logging.warning('This is a warning message')

import logging
# Create a logger
logger = logging.getLogger(__name__)
# Log some messages
logger.debug("This is a debug message.")
logger.info("This is an informational message.")
logger.warning("Careful! Something does not look right.")
logger.error("You have encountered an error.")
logger.critical("The program cannot recover from this situation!")

import logging
# Create a logger
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)
# Create a file handler
file_handler = logging.FileHandler('my_log.log')
logger.addHandler(file_handler)
# Create a console handler
console_handler = logging.StreamHandler()
logger.addHandler(console_handler)
# Log some messages
logger.debug("This is a debug message.")
logger.info("This is an informational message.")
logger.warning("Careful! Something does not look right.")
logger.error("You have encountered an error.")
logger.critical("The program cannot recover from this situation!")

import logging
# Create a logger
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)
# Create a console handler
console_handler = logging.StreamHandler()
# Create a formatter
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
# Add the formatter to the console handler
console_handler.setFormatter(formatter)
# Add the console handler to the logger
logger.addHandler(console_handler)
# Log some messages
logger.debug("This is a debug message.")
logger.info("This is an informational message.")
logger.warning("Careful! Something does not look right.")
logger.error("You have encountered an error.")
logger.critical("The program cannot recover from this situation!")

import logging
logger = logging.getLogger(__name__)
try:
    a = [1, 2, 3]
    value = a[3]
except IndexError as e:
    logger.error("Unhandled exception", exc_info=True)
		```
当运行此段代码，日志记录器将记录下出现的异常信息，如下：
```python
ERROR:__main__:Unhandled exception
Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
IndexError: list index out of range

import logging
from logging.handlers import RotatingFileHandler
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
# Create a file handler
handler = RotatingFileHandler('my_log.log', maxBytes=2000, backupCount=10)
logger.addHandler(handler)
# Log some messages
for _ in range(10000):
    logger.info("Hello, world!")
		```
##这段代码将在日志文件大小达到2000字节时创建一个新的日志文件，并保留最新的10个日志文件。
## 配置日志级别
##根据我们的需要，可以在运行时改变日志的级别。例如，当我们在调试应用程序时，我们可能需要输出所有级别的日志。但是在生产环境中，我们可能只关心错误及以上级别的日志。我们可以通过setLevel()函数来改变日志级别。如下例所示：
```python
import logging
# Create a logger
logger = logging.getLogger(__name__)
# Set log level to DEBUG
logger.setLevel(logging.DEBUG)
# Log some messages
logger.debug("This is a debug message.")
logger.info("This is an informational message.")
logger.warning("Careful! Something does not look right.")
logger.error("You have encountered an error.")
logger.critical("The program cannot recover from this situation!")

import logging
# Create a logger at the module level
logger = logging.getLogger(__name__)

import logging
import json
# Create a logger
logger = logging.getLogger(__name__)
# Log a structured message
logger.info(json.dumps({
    'action': 'User login',
    'username': 'user123',
    'ip_address': '123.123.123.123',
    'status': 'success',
}))

import logging
logger = logging.getLogger(__name__)
try:
    x = 1 / 0
except ZeroDivisionError:
    logger.exception("Zero Division Error Caught.")