sys.excepthook在导入模块中不起作用

Question

我正在设计一个Python程序，目的是记录所有未处理的异常，使用的是日志模块。我通过使用sys.excepthook这个函数来覆盖默认的异常处理方式。我发现如果我直接从命令行运行这个程序，它工作得很好，但如果我尝试导入这个文件，就不行了。看起来sys.excepthook函数对日志模块并不了解。下面是一个例子：

#! /usr/bin/env python2.7
import logging, sys

logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
logger.addHandler(logging.FileHandler("test.log"))

print "outside of exception handler: logger = %s" % logger

def handleException(excType, excValue, traceback):
    #global logger  # this function doesn't work whether or not I include this line
    print "inside exception handler: logger = %s" % logger
    logger.error("Uncaught exception", exc_info=(excType, excValue, traceback))

sys.excepthook = handleException

logger.debug("starting")
asdf    # create an exception

当我从命令行运行这个程序（./loggingTest.py）时，一切正常。异常会被记录下来，我看到这样的输出：

outside of exception handler: logger = <logging.RootLogger object at 0x7f2022eab950>
inside exception handler: logger = <logging.RootLogger object at 0x7f2022eab950>

但是，如果我启动Python解释器并尝试导入这个文件（import loggingTest），它就表现得很奇怪。异常没有被记录下来，我看到的是这样的：

outside of exception handler: logger = <logging.RootLogger object at 0x7f8ab04f3ad0>
inside exception handler: logger = None
Error in sys.excepthook:
Traceback (most recent call last):
  File "loggingTest.py", line 13, in handleException
    logger.error("Uncaught exception", exc_info=(excType, excValue, traceback))
AttributeError: 'NoneType' object has no attribute 'error'

Original exception was:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "loggingTest.py", line 18, in <module>
    asdf    # create an exception
NameError: name 'asdf' is not defined

我可能可以通过在sys.excepthook里面再次导入日志模块来解决这个问题，但我还是很好奇：为什么会这样呢？

Answer 1

我无法重现你遇到的错误，即使它发生在 exhook.py 文件里。这个文件的内容是：

#! /usr/bin/env python2.7
import logging, sys, traceback as tb

logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
logger.addHandler(logging.FileHandler("test.log"))

print "outside of exception handler: logger = %s" % logger

def handleException(excType, excValue, traceback):
    #global logger  # this function doesn't work whether or not I include this line
    tb.print_exception(excType, excValue, traceback)
    print "inside exception handler: logger = %s" % logger
    logger.error("Uncaught exception", exc_info=(excType, excValue, traceback))

sys.excepthook = handleException

raise Exception

然后：

Python 2.7 (r27:82525, Jul  4 2010, 09:01:59) [MSC v.1500 32 bit (Intel)] on win
32
Type "help", "copyright", "credits" or "license" for more information.
>>> import exhook
outside of exception handler: logger = <logging.RootLogger object at 0x02AB0A70>

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "exhook.py", line 18, in <module>
    raise Exception
Exception inside exception handler: logger = <logging.RootLogger object at 0x02AB0A70>

它运行得很好。你这边能正常工作吗？

Answer 2

我在Python的错误追踪系统上报告了这个问题，认为它是一个bug。到目前为止，有人回复说在Python 2.7和2.7.1之间确实有变化，他认为这是正常的行为。他还建议可以用下面的方式来记录所有的异常：

def handleException(excType, excValue, traceback, logger=logger):
    logger.error("Uncaught exception", exc_info=(excType, excValue, traceback))

sys.excepthook = handleException