En Mon, 23 Feb 2009 22:18:31 -0200, harijay <[email protected]> escribió:
mentioned here : ( http://www.dataq.com/support/techinfo/ff.htm)
I have a question about how to bitmask a bunch of bytes read in from
such a binary formatted file .
For eg the spec says the first two bytes have different parameters in
different bits .
Byte 1 Byte 0
SN16 SD9 SD8 SD7 SD6 SD5 SD4 SD3
SD2 SD1 SD0 T4 T3 T2 T1 T0
I am reading in the two bytes using the following code
import struct
f.seek(0)
element1_format = struct.Struct("<H")
(element1,) = element1_format.unpack(f.read(2))
Now element1 has type "str" .
No, should be type 'int', that's what the H format means.
How do I apply a bitmask to this to get
at information in the component bits .
Since the entire file format has many such bitmasked fields and since
this is my first venture into binary formats and c-type structs , I
wanted to know how to read values inside a byte using python.
My few tries at using bitwise operators ( element1 & 0x001f) are
frustrated by messages that say " unsupported operand type(s) for &:
'str' and 'int' " .
Try again - it should work. Perhaps you used the wrong variable name?
instead of the resultant from struct.unpack
py> import struct
py> element1_format = struct.Struct("<H")
py> (element1,) = element1_format.unpack('AB')
py> element1
16961
py> element1 & 0x007F
65
py> chr(65)
'A'
--
Gabriel Genellina
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