f-string: single '}' is not allowed Python SPARQL 查询问题

Question

我在使用 python 代码格式化 SPARQL 查询时遇到问题。显示的错误是：

  'SELECT Distinct ?article ?item ?itemLabel ?itemDescription (GROUP_CONCAT(DISTINCT(?entity_type); separator = ", ") AS ?entity_type_list) ?main_category ?wikipediaLabel (GROUP_CONCAT(DISTINCT(?altLabel); separator = ", ") AS ?altLabel_list)  WHERE'
                                                                                                                                                                                                                                                            ^
SyntaxError: f-string: single '}' is not allowed

我不知道我错过了什么，有人可以帮忙吗？

def search_wikidata_label(label,lang='ar'):
  sparql_query = (
'SELECT Distinct ?article ?item ?itemLabel ?itemDescription (GROUP_CONCAT(DISTINCT(?entity_type); separator = ", ") AS ?entity_type_list) ?main_category ?wikipediaLabel (GROUP_CONCAT(DISTINCT(?altLabel); separator = ", ") AS ?altLabel_list)  WHERE'
'{SERVICE wikibase:mwapi' 
         '{ bd:serviceParam wikibase:api "EntitySearch". bd:serviceParam wikibase:endpoint "www.wikidata.org".'
             f'bd:serviceParam mwapi:search "{label}".'
          f'bd:serviceParam mwapi:language "{lang}" .'
          '?item wikibase:apiOutputItem mwapi:item .'
          '?num wikibase:apiOrdinal true .}'
   '?item wdt:P31 ?entity_type .'
 'MINUS { ?item wdt:P31 wd:Q4167410}'
'OPTIONAL{    ?item wdt:P910 ?main_category}'
 'OPTIONAL { ?item skos:altLabel ?altLabel .' 
           f'FILTER (lang(?altLabel) = "{lang}") }'
 'OPTIONAL{ ?article schema:about ?item;schema:isPartOf <https://ar.wikipedia.org/>;schema:name ?wikipediaLabel}'
 'OPTIONAL{ ?article schema:about ?item;schema:isPartOf <https://ar.wikipedia.org/>;schema:name ?wikipediaLabel}'
 'SERVICE wikibase:label {'
  f'bd:serviceParam wikibase:language "{lang}" .}'
'}'
 'GROUP BY ?article ?item ?itemLabel ?itemDescription  ?main_category ?wikipediaLabel' 
    )
  #to query another endpoint, change the URL for the service and the query
  sparql_service_url = "https://query.wikidata.org/sparql"
  result_table = query_wikidata(sparql_query, sparql_service_url)
  return result_table

Answer 1

因为 SPARQL 在其语法中使用 { 和 }，并且因为您只替换了很少的值，所以我会避免使用 f 字符串并使用模板字符串，因为它使用 $ 来引入变量。更多信息见https://docs.python.org/3/library/string.html?highlight=string#template-strings。

如果你真的想坚持使用 f-string，那么在你希望结果中的文字 { 或 } 为 {{ 或 }} 的地方加倍 - 但这非常可怕，特别是如果你曾经想要更新查询。使用模板字符串，除了放入 $ 变量引用之外，您无需以任何方式修改查询。

此外，我发现将模板变量设为大写可以让它们更容易在模板中被发现，例如（我还整理了您的 SPARQL 布局）：

import string

sparql_query = '''
SELECT Distinct
    ?article
    ?item
    ?itemLabel
    ?itemDescription
    (GROUP_CONCAT(DISTINCT(?entity_type); separator = ", ") AS ?entity_type_list)
    ?main_category
    ?wikipediaLabel
    (GROUP_CONCAT(DISTINCT(?altLabel); separator = ", ") AS ?altLabel_list)
WHERE {
    SERVICE wikibase:mwapi
        {
            bd:serviceParam wikibase:api "EntitySearch". bd:serviceParam wikibase:endpoint "www.wikidata.org" .
            bd:serviceParam mwapi:search "$LABEL" .
            bd:serviceParam mwapi:language "$LANG" .
            ?item wikibase:apiOutputItem mwapi:item .
            ?num wikibase:apiOrdinal true .
        }
    ?item wdt:P31 ?entity_type .
    MINUS { ?item wdt:P31 wd:Q4167410}
    OPTIONAL {
            ?item wdt:P910 ?main_category
        }
    OPTIONAL {
            ?item skos:altLabel ?altLabel .
            f'FILTER (lang(?altLabel) = "$LANG")
       }
    OPTIONAL {
            ?article schema:about ?item;schema:isPartOf <https://ar.wikipedia.org/>;schema:name ?wikipediaLabel
        }
    OPTIONAL {
            ?article schema:about ?item;schema:isPartOf <https://ar.wikipedia.org/>;schema:name ?wikipediaLabel
        }
    SERVICE wikibase:label {
            bd:serviceParam wikibase:language "$LANG" .
        }
    }
GROUP BY ?article ?item ?itemLabel ?itemDescription  ?main_category ?wikipediaLabel
'''

result = string.Template(sparql_query).substitute( LANG="ENGLISH", LABEL="MYLABEL" )

print( result )

结果：

SELECT Distinct
    ?article
    ?item
    ?itemLabel
    ?itemDescription
    (GROUP_CONCAT(DISTINCT(?entity_type); separator = ", ") AS ?entity_type_list)
    ?main_category
    ?wikipediaLabel
    (GROUP_CONCAT(DISTINCT(?altLabel); separator = ", ") AS ?altLabel_list)
WHERE {
    SERVICE wikibase:mwapi
        {
            bd:serviceParam wikibase:api "EntitySearch". bd:serviceParam wikibase:endpoint "www.wikidata.org" .
            bd:serviceParam mwapi:search "MYLABEL" .
            bd:serviceParam mwapi:language "ENGLISH" .
            ?item wikibase:apiOutputItem mwapi:item .
            ?num wikibase:apiOrdinal true .
        }
    ?item wdt:P31 ?entity_type .
    MINUS { ?item wdt:P31 wd:Q4167410}
    OPTIONAL {
            ?item wdt:P910 ?main_category
        }
    OPTIONAL {
            ?item skos:altLabel ?altLabel .
            f'FILTER (lang(?altLabel) = "ENGLISH")
       }
    OPTIONAL {
            ?article schema:about ?item;schema:isPartOf <https://ar.wikipedia.org/>;schema:name ?wikipediaLabel
        }
    OPTIONAL {
            ?article schema:about ?item;schema:isPartOf <https://ar.wikipedia.org/>;schema:name ?wikipediaLabel
        }
    SERVICE wikibase:label {
            bd:serviceParam wikibase:language "ENGLISH" .
        }
    }
GROUP BY ?article ?item ?itemLabel ?itemDescription  ?main_category ?wikipediaLabel

Answer 2

如果你想有一个转义的大括号，你需要把它们加倍：

>>> lang = "lang"
>>> f'FILTER (lang(?altLabel) = "{lang}") }}'
'FILTER (lang(?altLabel) = "lang") }'
>>> f'FILTER (lang(?altLabel) = "{lang}") }'
  File "<stdin>", line 1
SyntaxError: f-string: single '}' is not allowed

检查：How can I print literal curly-brace characters in a string and also use .format on it?