{"record":{"id":"787d83489f9cb1e1","repo":"Textualize/textual","slug":"unable-to-parse-query-selector-r-as-a-query-che","errorCode":null,"errorMessage":"Unable to parse {query_selector!r} as a query; check for syntax errors","messagePattern":"Unable to parse (.+?) as a query; check for syntax errors","errorType":"exception","errorClass":"InvalidQueryFormat","httpStatus":null,"severity":"error","filePath":"src/textual/dom.py","lineNumber":1510,"sourceCode":"            if cached_result is not None:\n                return cached_result\n            if (\n                node := walk_breadth_search_id(\n                    base_node, query_selector[1:], with_root=False\n                )\n            ) is not None:\n                if expect_type is not None and not isinstance(node, expect_type):\n                    raise WrongType(\n                        f\"Node matching {query_selector!r} is the wrong type; expected type {expect_type.__name__!r}, found {node}\"\n                    )\n                base_node._query_one_cache[cache_key] = node\n                return node\n            raise NoMatches(f\"No nodes match {query_selector!r} on {base_node!r}\")\n\n        try:\n            selector_set = parse_selectors(query_selector)\n        except TokenError:\n            raise InvalidQueryFormat(\n                f\"Unable to parse {query_selector!r} as a query; check for syntax errors\"\n            ) from None\n\n        if all(selectors.is_simple for selectors in selector_set):\n            cache_key = (base_node._nodes._updates, query_selector, expect_type)\n            cached_result = base_node._query_one_cache.get(cache_key)\n            if cached_result is not None:\n                return cached_result\n        else:\n            cache_key = None\n\n        for node in walk_breadth_first(base_node, with_root=False):\n            if not match(selector_set, node):\n                continue\n            if expect_type is not None and not isinstance(node, expect_type):\n                raise WrongType(\n                    f\"Node matching {query_selector!r} is the wrong type; expected type {expect_type.__name__!r}, found {node}\"\n                )","sourceCodeStart":1492,"sourceCodeEnd":1528,"githubUrl":"https://github.com/Textualize/textual/blob/06dbeef4bb70fb718236aa418ed658ef4667a126/src/textual/dom.py#L1492-L1528","documentation":"query_one raises InvalidQueryFormat when the selector string cannot be tokenized/parsed by textual's CSS selector parser (TokenError from parse_selectors). This is a syntax error in the query, not a matching failure.","triggerScenarios":"Passing a malformed selector to query_one: unbalanced brackets, stray characters, invalid combinators, or a type name that isn't a valid identifier.","commonSituations":"Building selectors dynamically from user input or f-strings that produce empty/invalid fragments; copying browser-CSS selectors with syntax textual doesn't support; string concatenation bugs leaving trailing characters.","solutions":["Fix the selector syntax — use simple supported forms like '#id', '.class', 'Type', 'Type#id'","If constructing selectors dynamically, validate/strip components before joining","For type queries, pass the class itself (query_one(Input)) instead of a hand-built string"],"exampleFix":"# before\nself.query_one('Input#name extra:')  # unparseable\n\n# after\nself.query_one('Input#name')","handlingStrategy":"validation","validationCode":"from textual.css.tokenize import parse_selectors\ntry:\n    parse_selectors(selector)\nexcept Exception:\n    selector = sanitize(selector)  # or raise a clear config error\nself.query_one(selector)","typeGuard":"def is_valid_selector(s: str) -> bool:\n    try:\n        parse_selectors(s)\n        return True\n    except Exception:\n        return False","tryCatchPattern":"from textual.css.query import InvalidQueryFormat\ntry:\n    w = self.query_one(selector)\nexcept InvalidQueryFormat as e:\n    raise ConfigError(f'bad selector {selector!r}') from e","preventionTips":["Use static selector literals where possible","Validate dynamically built selectors in tests","Pass classes instead of strings for type queries"],"tags":["textual","query","selector","syntax"],"backgroundTag":"invalid-selector-syntax","analyzedSha":"06dbeef4bb70fb718236aa418ed658ef4667a126","analyzedAt":"2026-08-27T02:36:57.214Z","schemaVersion":2},"datasetVersion":"2026-08-27T03:17:27.898Z"}