sys.exc_info() 的行为在 python docs 中有描述。和 SO和 SO作为:
- 在 except block 或由 except block 调用的方法中,描述异常的三元组
- 在其他地方,三元组 None 值
那么为什么这个 nosetest 会失败呢?
def test_lang_stack(self):
try:
self.assertEquals((None,None,None), sys.exc_info()) # no exception
a = 5 / 0
except:
self.assertNotEquals((None,None,None), sys.exc_info()) # got exception
else:
self.fail('should not get here')
#finally:
# self.assertEquals((None,None,None), sys.exc_info()) # already handled, right?
self.assertEquals((None,None,None), sys.exc_info()) # already handled, right?
它在最后一行失败了。如果您取消注释 finally block ,它将在那里失败。
我确实看到,如果我将所有这些放在一个方法中并从另一个方法调用,那么调用方法就不会看到异常。 exc_info 值似乎仍设置为抛出异常的方法的末尾,即使在处理异常之后也是如此。
我在 OSX 上使用 python2.7。
最佳答案
在回答你的问题之前,我必须解释一下 sys.exc_info() 决定了你程序中最新/最近的异常:-
Your program is basically a series of function calls, with caller function calling called. Thus a call stack/execution stack is formed, where an entry is pushed for each function, being called. This entry is known as stack frame in python. Thus, when in your program, sys.exc_info() is invoked, it uses the following sequence to determining latest exception. It begins from the current stack frame, which is the function from where you are invoking sys.exc_info(). If the current stack frame is not handling/had not handled an exception, the information is taken from the calling stack frame, or its caller, and so on until a stack frame is found that is handling/had handled an exception . Here, “handling an exception” is defined as “executing or having executed an except clause.” For any stack frame, only information about the most recently handled exception is accessible.
现在,开始你的代码,
def test_lang_stack(self):
try:
self.assertEquals((None,None,None), sys.exc_info()) # no exception
a = 5 / 0
except:
self.assertNotEquals((None,None,None), sys.exc_info()) # got exception
else:
self.fail('should not get here')
#finally:
# self.assertEquals((None,None,None), sys.exc_info()) # already handled, right?
self.assertEquals((None,None,None), sys.exc_info()) # already handled, right?
按照上面解释的过程,sys.exc_info() 总是会发现最近在您的函数中处理的异常。因此,除非您显式调用 sys.exec_clear()
,否则它永远不会是 Nones 的元组。
希望对你有帮助。
关于python - sys.exc_info() 是如何工作的?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/16974489/