Python使用f-string拼接SPARQL查询报single '}' is not allowed错误求助

错误原因 #

你触发SyntaxError: f-string: single '}' is not allowed的核心原因是：

• Python的f-string语法里，{}是用来包裹插值变量的，单独出现的}会被识别为不合法的语法
• 你的SPARQL语句里包含大量SPARQL语法需要的单个}字符，这些字符和f-string的规则冲突了

解决方法 #

方法1：对SPARQL里所有不需要插值的}都加一个}转义 #

Python f-string里用两个连续的}}会被解析成单个}字符，你只要把所有不是用来包裹插值变量的{和}都替换成{{、}}即可，修改后代码如下：

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

方法2：改用format()方法做字符串拼接 #

把需要插值的位置先用{}占位，最后统一调用format传参，完全避开f-string的规则冲突：

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".'
             'bd:serviceParam mwapi:search "{}".'
          'bd:serviceParam mwapi:language "{}" .'
          '?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 .' 
           'FILTER (lang(?altLabel) = "{}") }'
 '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 "{}" .}'
'}'
 'GROUP BY ?article ?item ?itemLabel ?itemDescription  ?main_category ?wikipediaLabel' 
    ).format(label, lang, lang, lang)
  sparql_service_url = "https://query.wikidata.org/sparql"
  result_table = query_wikidata(sparql_query, sparql_service_url)
  return result_table

内容的提问来源于stack exchange，提问作者Mai