大家在开发的过程中可能时常碰到一个需求，需要把Python的异常信息输出到日志文件中。
网上的办法都不太实用，下面介绍一种实用的，从Python 2.7源码中扣出来的。
废话不说 直接上代码，代码不多，注释比较多而已。   
import sys, traceback

traceback_template = '''Traceback (most recent call last):
File "%(filename)s", line %(lineno)s, in %(name)s
%(type)s: %(message)s\n''' # Skipping the "actual line" item

# Also note: we don't walk all the way through the frame stack in this example
# see hg.python.org/cpython/file/8dffb76faacc/Lib/traceback.py#l280
# (Imagine if the 1/0, below, were replaced by a call to test() which did 1/0.)

try:
  1/0
except:
  # http://docs.python.org/2/library/sys.html#sys.exc_info
  exc_type, exc_value, exc_traceback = sys.exc_info() # most recent (if any) by default

  '''
  Reason this _can_ be bad: If an (unhandled) exception happens AFTER this,
  or if we do not delete the labels on (not much) older versions of Py, the
  reference we created can linger.

  traceback.format_exc/print_exc do this very thing, BUT note this creates a
  temp scope within the function.
  '''

  traceback_details = {
             'filename': exc_traceback.tb_frame.f_code.co_filename,
             'lineno' : exc_traceback.tb_lineno,
             'name'  : exc_traceback.tb_frame.f_code.co_name,
             'type'  : exc_type.__name__,
             'message' : exc_value.message, # or see traceback._some_str()
            }

  del(exc_type, exc_value, exc_traceback) # So we don't leave our local labels/objects dangling
  # This still isn't "completely safe", though!
  # "Best (recommended) practice: replace all exc_type, exc_value, exc_traceback
  # with sys.exc_info()[0], sys.exc_info()[1], sys.exc_info()[2]


  ## 修改这里就可以把traceback打到任意地方，或者存储到文件中了
  print traceback_template % traceback_details

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