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python - pyparsing.ParseException：预期 {SelectQuery | 构造查询 | 描述查询 | 询问查询}

问题描述

我在我的代码中运行以下 sparql，但出现错误。

def get_parents_of_node(node):
    sparql = """select ?superclass where {{ 
        :{0} rdfs:subClassOf* ?superclass
    }}""".format(node)
    q = g.query(sparql)
    for row in q:
        print row

get_parents_of_node('http://cccc.com#LaptopHighPerformance')

错误信息是

    Traceback (most recent call last):
  File "C:\Code\Python\RDF Parser\RDF_Parser.py", line 244, in <module>
    get_parents_of_node('http://cccc.com#LaptopHighPerformance')
  File "C:\Code\Python\RDF Parser\RDF_Parser.py", line 68, in get_parents_of_node
    q = g.query(sparql)
  File "C:\Python27\lib\site-packages\rdflib\graph.py", line 1085, in query
    query_object, initBindings, initNs, **kwargs))
  File "C:\Python27\lib\site-packages\rdflib\plugins\sparql\processor.py", line 74, in query
    parsetree = parseQuery(strOrQuery)
  File "C:\Python27\lib\site-packages\rdflib\plugins\sparql\parser.py", line 1058, in parseQuery
    return Query.parseString(q, parseAll=True)
  File "C:\Python27\lib\site-packages\pyparsing.py", line 1632, in parseString
    raise exc
pyparsing.ParseException: Expected {SelectQuery | ConstructQuery | DescribeQuery | AskQuery} (at char 36), (line:2, col:9)
[Finished in 3.8s with exit code 1]
[shell_cmd: python -u "C:\Code\Python\RDF Parser\RDF_Parser.py"]

标签： pythonrdflib

解决方案

阅读文档，您应该在initBindings调用时使用参数传递值（具有适当的类型）以将所需的查询变量映射到特定值query。例如：

def get_parents_of_node(node):
    sparql = """select ?superclass where {{ 
        ?class rdfs:subClassOf* ?superclass
    }}"""
    q = g.query(sparql, initBindings={'class': rdflib.URIRef(node)})
    for row in q:
        print row

这当然假设节点确实是一个 URI 引用。

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