At 10:20 PM 2/17/05 -0800, Andi Vajda wrote:
At 07:37 PM 2/17/05 -0800, Morgen Sagen wrote:raise takes 3 arguments:
http://www.python.org/doc/current/ref/raise.html#raiseYes, there it says.
But here, http://www.python.org/doc/current/lib/module-exceptions.html#l2h-280,
it doesn't (or I couldn't find it).
The bad part, is that I knew this, and had coded it right the first time. Upon reviewing the code, I found this 'bug' and 'fixed' it.
So, I fixed it again, this time commenting the unobvious, somewhat documented, use of the 3rd argument.
Just FYI, your fix is not thread-safe; if an error (even as simple as a transient KeyError or AttributeError) occurs in another thread between the __import__ and the raise statements, you will re-raise that thread's value and traceback, not the one you want. sys.exc_value and sys.exc_traceback have been deprecated for years because of this issue; see the sys module page referenced below. Naturally, for this particular use case it may not matter much, but it seems worth pointing out.
Anyway, the specific code in question should just use zero-argument raise, unless there's some reason that clients of ClassLoader want all exceptions to be transformed into ImportError, in which case the correct form would be this rather ugly three-argument form:
raise ImportError, ImportError(sys.exc_info()[1]), sys.exc_info()[2]
This is basically wrapping the original exception instance (exc_info()[1]) in an ImportError, and reusing the traceback. I'm using sys.exc_info() instead of sys.exc_value and exc_traceback because those variables are not threadsafe nor frame-specific, as exc_info() is. (See http://www.python.org/doc/current/lib/module-sys.html for details.)
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