How to use the bitstring.bitstore.offsetcopy function in bitstring

def _reversebytes(self, start, end):
        """Reverse bytes in-place."""
        # Make the start occur on a byte boundary
        # TODO: We could be cleverer here to avoid changing the offset.
        newoffset = 8 - (start % 8)
        if newoffset == 8:
            newoffset = 0
        self._datastore = bitstore.offsetcopy(self._datastore, newoffset)
        # Now just reverse the byte data
        toreverse = bytearray(self._datastore.getbyteslice((newoffset + start) // 8, (newoffset + end) // 8))
        toreverse.reverse()
        self._datastore.setbyteslice((newoffset + start) // 8, (newoffset + end) // 8, toreverse)

# Just overwriting with self, so do nothing.
            assert pos == 0
            return
        firstbytepos = (self._offset + pos) // 8
        lastbytepos = (self._offset + pos + bs.len - 1) // 8
        bytepos, bitoffset = divmod(self._offset + pos, 8)
        if firstbytepos == lastbytepos:
            mask = ((1 << bs.len) - 1) << (8 - bs.len - bitoffset)
            self._datastore.setbyte(bytepos, self._datastore.getbyte(bytepos) & (~mask))
            d = bitstore.offsetcopy(bs._datastore, bitoffset)
            self._datastore.setbyte(bytepos, self._datastore.getbyte(bytepos) | (d.getbyte(0) & mask))
        else:
            # Do first byte
            mask = (1 << (8 - bitoffset)) - 1
            self._datastore.setbyte(bytepos, self._datastore.getbyte(bytepos) & (~mask))
            d = bitstore.offsetcopy(bs._datastore, bitoffset)
            self._datastore.setbyte(bytepos, self._datastore.getbyte(bytepos) | (d.getbyte(0) & mask))
            # Now do all the full bytes
            self._datastore.setbyteslice(firstbytepos + 1, lastbytepos, d.getbyteslice(1, lastbytepos - firstbytepos))
            # and finally the last byte
            bitsleft = (self._offset + pos + bs.len) % 8
            if not bitsleft:
                bitsleft = 8
            mask = (1 << (8 - bitsleft)) - 1
            self._datastore.setbyte(lastbytepos, self._datastore.getbyte(lastbytepos) & mask)
            self._datastore.setbyte(lastbytepos,
                                    self._datastore.getbyte(lastbytepos) | (d.getbyte(d.bytelength - 1) & ~mask))
        assert self._assertsanity()

def _inplace_logical_helper(self, bs, f):
        """Helper function containing most of the __ior__, __iand__, __ixor__ code."""
        # Give the two bitstrings the same offset (modulo 8)
        self_byteoffset, self_bitoffset = divmod(self._offset, 8)
        bs_byteoffset, bs_bitoffset = divmod(bs._offset, 8)
        if bs_bitoffset != self_bitoffset:
            if not self_bitoffset:
                bs._datastore = bitstore.offsetcopy(bs._datastore, 0)
            else:
                self._datastore = bitstore.offsetcopy(self._datastore, bs_bitoffset)
        a = self._datastore.rawbytes
        b = bs._datastore.rawbytes
        #assert a.bytelength == b.bytelength
        for i in xrange(len(a)):
            a[i] = f(a[i + self_byteoffset], b[i + bs_byteoffset])
        return self

"""
        if isinstance(bs, Bits):
            return bs
        try:
            return cache[(bs, offset)]
        except KeyError:
            if isinstance(bs, basestring):
                b = cls()
                try:
                    _, tokens = tokenparser(bs)
                except ValueError as e:
                    raise bitstring.CreationError(*e.args)
                if tokens:
                    b._append(Bits._init_with_token(*tokens[0]))
                    b._datastore = bitstore.offsetcopy(b._datastore, offset)
                    for token in tokens[1:]:
                        b._append(Bits._init_with_token(*token))
                assert b._assertsanity()
                assert b.len == 0 or b._offset == offset
                cache[(bs, offset)] = b
                return b
        except TypeError:
            # Unhashable type
            pass
        return cls(bs)

def _inplace_logical_helper(self, bs, f):
        """Helper function containing most of the __ior__, __iand__, __ixor__ code."""
        # Give the two bitstrings the same offset (modulo 8)
        self_byteoffset, self_bitoffset = divmod(self._offset, 8)
        bs_byteoffset, bs_bitoffset = divmod(bs._offset, 8)
        if bs_bitoffset != self_bitoffset:
            if not self_bitoffset:
                bs._datastore = bitstore.offsetcopy(bs._datastore, 0)
            else:
                self._datastore = bitstore.offsetcopy(self._datastore, bs_bitoffset)
        a = self._datastore.rawbytes
        b = bs._datastore.rawbytes
        #assert a.bytelength == b.bytelength
        for i in xrange(len(a)):
            a[i] = f(a[i + self_byteoffset], b[i + bs_byteoffset])
        return self