How do I use the unpack function?

[Marlin Rowley]

Sorry Gary,
 
I found out that I wasn't reassigning the array back once I got the first 4 bytes.  I don't mean to appear lazy..:(
 
Thanks for the help!
 
-M



> Date: Thu, 15 May 2008 09:51:22 -0700> From: gherron at islandtraining.com> To: marlin_rowley at hotmail.com> CC: python-list at python.org> Subject: Re: How do I use the unpack function?> > Marlin Rowley wrote:> > Thanks for the advice!> > > > However, I assumed that:> > > > fourbytes = pixelComponent[:4]> > > > would shave that byte off the array in pixelComponent. So that the > > array is smaller by one on the next iteration. Is this not the case?> You don't need the newsgroup to answer this kind of question. Just try it!> > >>> a = 'abcdefghi'> >>> b = a[:4]> >>> print a,b> abcdefghi abcd> > Notice that the [:4] index does not change the original array.> > Gary Herron> > > > > > > I'm getting weird results now..> > > > -M> >> >> >> >> > ------------------------------------------------------------------------> >> > > Date: Thu, 15 May 2008 09:11:23 -0700> > > From: gherron at islandtraining.com> > > To: marlin_rowley at hotmail.com> > > CC: python-list at python.org> > > Subject: Re: How do I use the unpack function?> > >> > > Marlin Rowley wrote:> > > > All:> > > >> > > > I've got a script that runs really slow because I'm reading from a> > > > stream a byte at a time:> > > >> > > > // TERRIBLE> > > > for y in range( height ):> > > > for color in range(4):> > > > for x in range( width ):> > > > pixelComponent = fileIO.read(4)> > > > buffer = unpack("!f",pixelComponent) << unpacks ONE> > > > float, but we now can do something with that pixel component.> > > >> > > >> > > > I can speed this up dramatically if I did this:> > > >> > > > // MUCH FASTER> > > > for y in range( height ):> > > > for color in range(4):> > > > pixelComponent = fileIO.read(4*width) <<<<<<<<< GET a LOT more> > > > data from the stream into memory FIRST!!> > > > for x in range( width ):> > > > buffer = unpack( ?????? ) <<<< how do I get each float from> > > > the pixelComponent???> > >> > > Just carve of the first four bytes of pixelComponent on each pass> > > through the loop, and unpack that.> > >> > > for x in range(width):> > > fourbytes = pixelComponent[:4] # first 4 bytes> > > pixelComponent = pixelComponent[4:] # All but first four bytes> > > buffer = unpack("!f", fourbytes)> > >> > >> > > There are probably better ways overall, but this directly answers your> > > question.> > >> > > Gary Herron> > >> > >> > > >> > > >> > > > -M> > > > > > ------------------------------------------------------------------------> > > > With Windows Live for mobile, your contacts travel with you. Connect> > > > on the go.> > > > > > <http://www.windowslive.com/mobile/overview.html?ocid=TXT_TAGLM_WL_Refresh_mobile_052008> > >> > > >> > > > > > ------------------------------------------------------------------------> > > >> > > > --> > > > http://mail.python.org/mailman/listinfo/python-list> > >> >> >> > ------------------------------------------------------------------------> > Get Free (PRODUCT) RED™ Emoticons, Winks and Display Pics. Check it > > out! > > <http://joinred.spaces.live.com?ocid=TXT_HMTG_prodredemoticons_052008>> > ------------------------------------------------------------------------> >> > --> > http://mail.python.org/mailman/listinfo/python-list> 
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