getting at individual bits inside byte field: struct module : bitwise operator

[harijay]

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