algebra.py 文件源码

def reorderTriples(l):
    """
    Reorder triple patterns so that we execute the
    ones with most bindings first
    """

    def _addvar(term, varsknown):
        if isinstance(term, (Variable, BNode)):
            varsknown.add(term)

    l = [(None, x) for x in l]
    varsknown = set()
    varscount = collections.defaultdict(int)
    for t in l:
        for c in t[1]:
            if isinstance(c, (Variable, BNode)):
                varscount[c] += 1
    i = 0

    # Done in steps, sort by number of bound terms
    # the top block of patterns with the most bound terms is kept
    # the rest is resorted based on the vars bound after the first
    # block is evaluated

    # we sort by decorate/undecorate, since we need the value of the sort keys

    while i < len(l):
        l[i:] = sorted((_knownTerms(x[
                       1], varsknown, varscount), x[1]) for x in l[i:])
        t = l[i][0][0]  # top block has this many terms bound
        j = 0
        while i+j < len(l) and l[i+j][0][0] == t:
            for c in l[i+j][1]:
                _addvar(c, varsknown)
            j += 1
        i += 1

    return [x[1] for x in l]