operators.py 文件源码

def Builtin_COALESCE(expr, ctx):
    """
    http://www.w3.org/TR/sparql11-query/#func-coalesce
    """
    for x in expr.get('arg', variables=True):
        if x is not None and not isinstance(x, (SPARQLError, Variable)):
            return x
    raise SPARQLError(
        "COALESCE got no arguments that did not evaluate to an error")