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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_bytes(self, index, size):
 """ Extracts several bytes from a bitvector, where the index refers to the byte in a big-endian order :param index: the byte index at which to start extracting :param size: the number of bytes to extract :return: A BV of size ``size * 8`` """

        pos = self.size() // 8 - 1 - index
        return self[pos * 8 + 7 : (pos - size + 1) * 8]