When teaching Python, do we begin with a treatment of
low level representations of data?  Or is that saved for
a later time?

For example:

   > >> import struct,array,sys
   > >> sys.byteorder
   'little'
   > >> m = array.array('I','THIS')
   > >> m
   array('I', [1397311572L])
   > >> k = [hex(ord(i))[2:] for i in 'THIS']
   > >> k.reverse()
   > >> k
   ['53', '49', '48', '54']
   > >> k = "".join(k)
   > >> k
   '53494854'
   > >> eval('0x'+k)
   1397311572
   > >> struct.pack('i',1397311572)
   'THIS'

Basically, I'm taking the string 'THIS' and converting
it to an integer.  The way this is done internally
corresponds to concatenating 4 hex bytes in reverse
order, i.e. 'T' = 0x54:

   > >> ord('T')
   84
   > >> hex(84)
   '0x54'

Link those bytes to return a bigger number in decimal
form (1397311572).  Then tell struct it's reading an
integer, which it returns as a corresponding string:
lo and behold, our THIS is returned to us.

Kirby



_______________________________________________
Edu-sig mailing list
Edu-sig@[...].org
http://mail.python.org/mailman/listinfo/edu-sig