Generate tuples of pairs of records from a block of records

        Arguments:

        blocks -- an iterable sequence of blocked records

def _blockedPairs(self, blocks):
        """
        Generate tuples of pairs of records from a block of records

        Arguments:

        blocks -- an iterable sequence of blocked records
        """

        block, blocks = core.peek(blocks)
        self._checkBlock(block)

        combinations = itertools.combinations

        pairs = (combinations(sorted(block), 2) for block in blocks)

        return pairs