Winter Madness - Passing Python objects as Strings
gagsl-py2 at yahoo.com.ar
Sat Jun 6 06:43:37 CEST 2009
En Fri, 05 Jun 2009 12:33:04 -0300, Hendrik van Rooyen
<mail at microcorp.co.za> escribió:
> "Gabriel Genellina" <ga..y2 at yahoo.com.ar> wrote:
>> But if you already have a queue, you may put other objects there
>> of "canning" them). Testing the object type with isinstance(msg, str) is
>> pretty fast, and if you bind locally those names I'd say the overhead is
> Maybe you are right and I am pre optimising - but the heart of this
> box really is that silly loop and the processor really is not fast at
From your description of the problem, it seems you are acting upon
messages received from a serial port. You have to process the message
*before* the next one arrives -- but you gain nothing doing that much
faster. In other words, even with a blazingly fast processor, you can't do
things faster than the rate of incoming messages.
In any case, you have to test-and-branch in the code. Either with
isinstance(rec,str), either with rec_list=="B", or something. I'm
unsure if this is the fastest approach - intuition doesn't play well with
timings in Python, better to actually measure times.
> This is what I was trying to avoid, as it is important to get as much
> performance out of the box as I can (given that I am using Python to
> get the job done fast, because that is also important). So it is a kind
> juggling with priorities - "make it fast" would imply do not use python,
> but "get it done quickly" implies using python, and it looks to me that
> if I am careful and think more like an assembler programmer, the
> real time performance will be adequate. And I do not want to do
> anything that could conceivably compromise that. Even if it means
> jumping through a funny hoop like I am doing now, and inventing
> a weird way to pass an object.
If it works and you feel it's adequate, that's fine. I cannot count how
many times I've used an integer property to attach a pointer to another
object (in other languages), but I felt "dirty" doing that. And never did
something like that in Python...
> So to a large extent I think that I am doing the job as fast as it is
> possible - the comma delimited input string is a fact, decided on
> between myself and the customer a long time ago, and it comes over
> a socket, so it has to be a string. The least I can do with it is
> before I put it on the critical queue. Then when it comes out of the
> queue, I have to break it up into its constituent parts, and I would
> that split is the canonical way of doing that.
Ok, what if you split *before* putting in the queue? In the receiving side
of the queue, just remove the split(",") part (it's already done). This
does not add anything to the critical path - the split must be done anyway.
Now, instead of building a fake string "B,cannedobject" and uncanning on
the other side, you can simply put a tuple in the queue ("B", the_object)
and just get the object on the other side. If I'm not misunderstanding
your problem, I think this is the cleanest way to do that.
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