"harijay" <hari...@gmail.com> wrote in message news:4c7d58a1-830f-4f02-ba07-aa4910f5f...@b16g2000yqb.googlegroups.com...
In my last post I had asked about reading data from a binary file using the struct module. Thanks to some excellent help , I have managed to read in successfully most of the header of this binary format that I want to parse. These are some time-voltage traces from a digital to analog converter for my experiments. The output is according to a format 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" . 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' " . How can I keep my string objects as bits and apply bitmasks to them Any help in this will be greatly appreciated. Thanks hari
Please post a small example that fails as you describe. From your example, element1 should be an int (unpacked from two bytes), and there is no f defined. Without the actual code we can't figure out what you are doing wrong.
This works as expected:
import struct format = struct.Struct("<H") (element1,) = format.unpack('aa') # a two-byte string to unpack print hex(element1)
0x6161
print element1 & 0x1f
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