[Python-talk] struct pack

[Lloyd Kvam]

On Thu, 2009-08-27 at 12:01 -0400, bruce.labitt at autoliv.com wrote:
> Is there a way to use struct.pack on an array? or a list?
> 
> # CME
> from struct import pack, unpack
> from numpy import array, random
> 
> anum = random.normal(0., 0.1, 10)       # make array of 10 random numbers
> fmt = '!'+str(anum.size)+'d'            # code as 10 doubles, network 
> order
> 
> apackt = pack( fmt, anum )              # <== pseudo-code, but that is my 
> intent...

In [11]: apackt = pack( fmt, *anum )              # <== pseudo-code,

pack expects separate args after the format string.
The * notation explodes a sequence into separate args to fit the pack
function signature.

> apack = array(apackt)                   # convert returned tuple to an 
> array
> 
> 
> One gets the error, "error: pack requires exactly 10 arguments"
> 
> Is there a way to do this besides processing each element and 
> concatenating all the resultant strings?  I would imagine this to be quite 
> slow for 308 x 32K byte strings = 1 FFT
> 
> I did not understand the Section 8.3.1 Struct Objects. 
> http://docs.python.org/library/struct.html
> 
> Can someone provide a simple example (somewhat like above) that uses 
> struct objects?
> 
> Supposedly using struct objects is faster.  If I have to process every 
> element, it could be useful.
> 
> Thanks!
> Bruce
> 
> Bruce Labitt
> Autoliv Electronics
> 1011B Pawtucket Blvd, PO Box 1858
> Lowell, MA  01853
> 
> Email: bruce.labitt at autoliv.com. 
> Tel:  (978) 674-6526
> Fax: (978) 674-6581 
> 
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Lloyd Kvam
Venix Corp
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