Hi Charles, Yes, twistd doesn't appear to work on py3k. Not being able to import _preamble is normal (once Twisted has been installed), but _preamble does assume sys.exc_clear exists, which isn't true on 3.x. I couldn't find any ticket on this. Perhaps you should file it (and maybe fix it!) :) It's my understanding that the new except clause semantics are expected to take care of this problem. Can someone comment as to why this was put there in the first place, and, specifically, why it can't just be "pass"? Is there some logging system that looks at the current exception or something when twistd (or some other script) starts? cheers lvh

On Tue, Sep 17, 2013 at 2:14 PM, wrote:

I think there are still many unported dependencies of `twistd` to port first.

Sure, but every little bit helps, right? :)

Can someone comment as to why this was put there in the first place, and,

...

specifically, why it can't just be "pass"? Is there some logging system that looks at the current exception or something when twistd (or some other script) starts?

Both `log.err()´ and `Failure()´ look at the current exception. If we don't `sys.clear_exc()´ here then the first piece of code that tries to use either of those may get a surprising result. The current exception state can last a long time so this surprise can hide for a remarkably long time before showing up.

Okay, cool. From what I understand: 1. _preamble is just a hack to get bin/whatever to work right without installing (i.e. from a checkout) 2. (not too sure about this) in py3k, except statements do the clearing bit already: www.python.org/dev/peps/pep-3110/#semantic-changes So, does that mean we can do a try: ... ; except AttributeError and be done with it? The exception state also holds references to lots of extra things on the

stack which is undesirable even if there are no other side-effects.

Jean-Paul

lvh

Jean-Paul 您好！ Thanks for your help. Because i am a fresh man to twisted. I will roll back to version 2.x and try the application again. 谢谢！！ ---------------------------- 姓名 : 吴志高/Charles 电话 : (+086)13410859946 邮箱 : wuzhigaoem@163.com ================================================ At 2013-09-17 20:14:08,exarkun@twistedmatrix.com wrote:

On 09:06 am, _@lvh.io wrote:

...

Hi Charles,

Yes, twistd doesn't appear to work on py3k. Not being able to import _preamble is normal (once Twisted has been installed), but _preamble does assume sys.exc_clear exists, which isn't true on 3.x.

I couldn't find any ticket on this. Perhaps you should file it (and maybe fix it!) :)

I think there are still many unported dependencies of `twistd` to port first.

...

It's my understanding that the new except clause semantics are expected to take care of this problem.

Can someone comment as to why this was put there in the first place, and, specifically, why it can't just be "pass"? Is there some logging system that looks at the current exception or something when twistd (or some other script) starts?

Both `log.err()´ and `Failure()´ look at the current exception. If we don't `sys.clear_exc()´ here then the first piece of code that tries to use either of those may get a surprising result. The current exception state can last a long time so this surprise can hide for a remarkably long time before showing up.

The exception state also holds references to lots of extra things on the stack which is undesirable even if there are no other side-effects.

Jean-Paul

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