struct->bit access

[Phil Frost]

It's not slow or complicated. Try something like this:


import struct

class Example(object):
  def __init__(data):
    '''data is a string of 4 bytes read from your input socket.'''
    (i,) = struct.unpack('!I', data)
    self.var1 = i & 7
    self.var2 = (i >> 3) & 7
    self.var3 = (i >> 6) & 1
    self.var4 = (i >> 8) & 0xf
    self.var5 = (i >> 16) & 0xff


You might want to change the format string for unpack() depending on the
byte order of the input.
<http://python.org/doc/2.3.4/lib/module-struct.html> has more
information.

On Mon, Sep 13, 2004 at 07:58:23AM -0700, Mike Spindler wrote:
> I am passing structs via UDP socket to my Python app from an external
> C program.  The structure is made up almost entirely of bit fields.
>  
> struct example: 
>  unsigned int var1 : 3;
>  unsigned int var2 : 3;
>  unsigned int var3 : 1;
>  unsigned int pad1 : 1;
>  unsigned int var4 : 8;
>  unsigned int var5 : 16;
> 
> Everything I've read so far says this is too complicated and slow for
> Python - write it in C.  Can someone point me to a good example of
> extracting this and rebuilding using only Python?
> Thank you!  -Mike