Winter Madness - Passing Python objects as Strings
Hendrik van Rooyen
mail at microcorp.co.za
Fri Jun 5 10:54:47 CEST 2009
<skip at pobox.com> wrote:
> Got some use cases?
plural cases - no.
I did it for the reason already described.
to elucidate, the code looks something like this:
rec = input_q.get() # <=== this has its origen in a socket, as a netstring.
reclist = rec.split(',')
if reclist == 'A':
do something with the outputs
get hold of the latest inputs
return the result by putting a message on the normal output q.
# up to here this is the code that is done in 99.9999% of cases.
# note that it has to run as fast as possible, in a very cripple processor.
if reclist == "B": # This means we have to change state,
# it comes from another thread that did
# not exist before an event.
new_output_q = uncan(reclist) # <== This is where it is used
do similar stuff until normality is re established,
discarding the incoming "A" records,
using new "C" records and new_output_q.
Terminated by a "D" record.
It is simply a different way of saying "use this one",
in an in band way.
In the above, it avoids a double unpacking step - once to
get to the record type, and then to get to the actual data.
It only makes sense here because I know that the stuff
that comes in is basically an unending stream of more
of the same, and it happens - I would say thousands of
times a second, but it is more like a hundred or so, given
the lack of speed of the processor.
So I am quite prepared to trade off the slight inefficiency
during the seldom occurring changeover for the railroad
like chugging along in the vast majority of cases.
"seldom" here is like once a day for a few minutes.
And it sure beats the hell out of passing the queue
name as a string and mucking around with exec or eval -
That is what I did first, and I liked it even less,
as the queue passed in such a way had to be a global
for the exec to work.
It all started because I was not prepared to waste
precious cycles in an extra unpacking stage.
So I wrote the Can extension module, and
I thought it weird enough to make it public: -
Hands up those who have ever passed a
pointer as a string !
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