当我不处理它时如何打印异常?

How to print an exception when I'm not handling it?

我有以下代码:

# exc is a local variable of type Exception
# This is not inside an except block
if isinstance(exc, ClientError):
    logging.debug("ClientError raised while loading %s:\n%s", package.id, traceback.format_exc())
    continue

当此代码为 运行 且 excClientError 类型时,format_exc() 仅打印出 NoneType: None,因为当前未处理任何异常(代码不在 except 块内)。幸运的是 traceback 上似乎有 format_exception 方法,它与当前正在处理的异常无关,但为了调用它,我需要从中提取类型、值和 tb我的异常变量。我该怎么做?

exc 是如何产生的?如果它是从某个没有相应堆栈的函数 return 编辑的,那么无论如何都不可能生成正确的帧。最重要的是,没有 going deep into ctypes 就不可能生成 Traceback 对象,所以这可能不是我们想要的。

如果您所追求的实际上是记录异常的堆栈,那么使用 inspect.currentframe and traceback.format_stack 可能会产生您所追求的结果。但是,如前所述,您需要获取尽可能接近错误发生位置的帧。考虑这个例子:

import traceback
import inspect
import logging


class Client:
    pass


class ClientError(Exception):
    pass


def get_client(name):
    if name is None:
        return ClientError('client must have a name')
    return Client()


def connect(target, name=None):
    exc = get_client(name)
    if isinstance(exc, ClientError):
        frames = inspect.currentframe()
        logging.debug("ClientError raised while loading %s:\n%s",
            target, ''.join(traceback.format_stack(frames)))


def main():
    connect('somewhere')


if __name__ == '__main__':
    logging.basicConfig(level=logging.DEBUG)
    main()

执行此操作将产生以下输出:

DEBUG:root:ClientError raised while loading somewhere:
  File "foo.py", line 34, in <module>
    main()
  File "foo.py", line 30, in main
    connect('somewhere')
  File "foo.py", line 26, in connect
    target, ''.join(traceback.format_stack(frames)))

请注意,堆栈恰好在调用完成的位置结束,因为 current_frame 的 return 值限制为 frames。这就是为什么堆栈应该在它产生的地方生成和格式化,并退后一层。考虑这些更新的功能:

def get_client(name):
    if name is None:
        return (
            ClientError('client must have a name'),
            traceback.format_stack(inspect.currentframe().f_back),
        )
    return Client(), None


def connect(target, name=None):
    exc, frames = get_client(name)
    if isinstance(exc, ClientError):
        stack = ''.join(frames)
        logging.debug("ClientError raised while loading %s:\n%s",
            target, stack)

执行

$ python foo.py 
DEBUG:root:ClientError raised while loading somewhere:
  File "foo.py", line 37, in <module>
    main()
  File "foo.py", line 33, in main
    connect('somewhere')
  File "foo.py", line 25, in connect
    exc, frames = get_client(name)

注意跟踪是如何在产生异常的函数处结束的。