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```#
# bitfield manipulation
#

class bf(object):
def __init__(self,value=0):
"Init bitfield with a value int in bin, hex, oct or dec"
self._d = value

def __getitem__(self, index):
"return bit value for that index (n-0)"
return (self._d >> index) & 1

def __setitem__(self,index,value):
"set bit value for that index (n-0)"
value    = (value&1)<<index
self._d  = (self._d & ~mask) | value

def __getslice__(self, start, end):
"return bits slice from start to end (n-0)"
mask = 2**(end - start + 1) -1
return ((self._d >> start) & mask)

def __setslice__(self, start, end, value):
"set bits slice from start to end index (n-0) with the given value"
mask = 2**(end - start + 1) -1
value = (value & mask) << start
self._d = (self._d & ~mask) | value
return (self._d >> start) & mask

def __int__(self):
"add de int() function for bf"
return self._d

def int(self):
"add the bf.int() function return int"
return self._d

def bin(self):
"add the bf.bin() function return str"
return '{0:0b}'.format(self._d)

def hex(self):
"add the bf.hex() function return str"
return '{0:0x}'.format(self._d)

def __repr__(self):
"add the basic return function, return bin str"
return '{0:0b}'.format(self._d)

def __len__(self):
"add the len() function return int with the bit number count"
return len('{0:0b}'.format(self._d))

def unpack(self,pack):
"return the unpack bit fields in dec [ n1, n2, n3...] with length given in pack [ l1, l2, l3...]"
r=[]; ss=0;pack.reverse()
for i in pack:
r.append(self.__getslice__(ss,ss+i-1))
ss +=i
r.reverse()
return  r

def pack(self,pack):
"return bf with the given values in dec [n1, n2, n3...] packed"
r=bf(); ss=0;pack.reverse()
for i in pack:
l1=len(bin(i))-2
r.__setslice__(ss,ss+l1,i)
ss +=l1
return  r

if __name__ == "__main__":

k = bf(0x0f)
k[10:20] =0xfffffffffff
k[3:7]=0b10101
print k[3]
print k[5]

print k
print len(k)

print k.unpack([5, 3,1,7]),(k.unpack([5, 3,1,7]))[1]
b1,b2,b3,b4 =  k.unpack([5, 3,1,7])
print b1,b2,b3,b4

print bf().pack([0b1101,0b1001])
```