Comments on: Aren’t django signals a little like comefrom?

By: Kelvin71

Kelvin71 — Fri, 23 Oct 2009 02:08:56 +0000

Ask yourself these seven questions to determine what type of learner you are: If you would choose to read about it you are more of a visual learner, if you would prefer to hear about it you are a more auditory learner and if you would like to try it yourself you are more of a tactile learner. ,

By: Gonzalo Delgado

Gonzalo Delgado — Mon, 20 Jul 2009 02:20:17 +0000

So you're saying the observer pattern is a bit like comefrom.. interesting.

By: 悉尼

悉尼 — Mon, 20 Jul 2009 01:56:28 +0000

yes, it’s a little bit like comefrom…

By: bill jones

bill jones — Sun, 19 Jul 2009 22:26:24 +0000

The similarity is superficial.

COMEFROM (and GOTO) are both static - in that they are defined when the code is written and cannot be changed at runtime. Signal-based connections can be created or removed at runtime.

Any number of signal handlers can respond to a single event, whereas COMEFROM/GOTO only transfer control flow from point A to point B (not B1, B2... Bn).

Also, I'm pretty sure your COMEFROM based translation of the signal example could not possibly work. For example, what's the actual entry point to the 'handle_num_comments' function? The fact that you can't create a corresponding example (that actually works) kind of proves the point that these structures are not equivalent.

By: Max Battcher

Max Battcher — Sun, 19 Jul 2009 21:57:27 +0000

Although “GOTO is considered harmful”, no one has proven that COMEFROM is harmful. In the case of INTERCAL, COMEFROM is a nightmare because it is the only real flow-control mechanism in the language and requires some mind-bending to actually accomplish more straightforward patterns. Django signals doesn’t suffer from the same problems as COMEFROM, because ultimately it is not the only flow-control mechanism in Django/Python. Signals are merely a nice aspect-oriented/event-oriented support tool that is one in a large bag of useful tools.

By: Douglas

Douglas — Sun, 19 Jul 2009 13:33:01 +0000

The difference between COMEFROM and event handling/post_save, is that control does not return back to the label after COMFROM.

Example: register_post_save_handler(); save(); // handler called here now_this_is_called();

register_COMEFROM_post_save(); save(); // handler called here this_may_not_get_called,_call_stack_gone();

By: K

Sun, 19 Jul 2009 09:09:51 +0000

I haven’t looked at Django, but it seems like basic event handling to me. If so, you could say that all event handling is a lot like COMEFROM

By: mjc

mjc — Sun, 19 Jul 2009 05:11:30 +0000

I remember in the 70′s studying the semantics of programming languages and coming across this definition of the semantics of a label: The condition true at a label is the union (logical or) of all the conditions true at the places where the next statement (via goto or falling through) is the label. This seemed (1) true after it is pointed out, and (2) a lot like the COMEFROM.