Whoosh’s query syntax is configurable: its whoosh.qparser parser uses plugins to recognize and transform syntax, then produces query objects from whoosh.query. You can remove unwanted features, change operator words, or add features such as fuzzy matching—so the language presented to users does not have to be the default one. The examples and API details below are documented for Whoosh 2.7.4; check them against the version installed in your project.
What the parser does
A query parser translates a user-entered string into a query object or tree that Whoosh can execute. The default language is similar to Lucene’s. For example, the guide shows rendering shading becoming an And query containing two Term objects.
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A QueryParser is constructed with a default field and a schema. The default field is where unqualified terms are searched; the schema’s field types determine how text is analyzed before query objects are created. This means parser syntax and index design are connected: enabling a syntax does not guarantee that the underlying field can support it.
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Start with the default language and its constraints
The default query language includes terms and phrases, Boolean operators, and field-qualified searches; the guide also describes ranges, prefix searches, and wildcards. The default grouping is AndGroup, so adjacent terms are required by default. You can choose another grouping, such as OrGroup, when the application should treat unconnected terms as alternatives instead.
Phrase search depends on the field’s index data. The field must store positional information; otherwise a phrase query cannot be evaluated, and Whoosh raises QueryError by default. Check the schema as well as the parser when exposing phrase syntax.
A parser can be created without a schema to inspect parser output, but the documentation says it will not process query text in that configuration. That can help when examining syntax structure; it is not a substitute for configuring the schema used to build executable queries. The default query language guide describes the syntax and field constraints.
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Choose which syntax users can enter
Remove fielded searches or wildcards
To prevent users from naming fields in their queries, the guide removes FieldsPlugin. To remove wildcard syntax, remove WildcardPlugin. Whoosh’s guide recommends this as one way to avoid potentially harmful query performance from wildcard searches; it does not give a benchmark or guarantee a particular performance outcome.
If prefix matching is sufficient, the API describes removing WildcardPlugin and adding PrefixPlugin. This keeps a narrower matching feature without exposing the full wildcard syntax.
Change Boolean operator words
You can replace OperatorsPlugin to change the tokens users type for AND, OR, ANDNOT, ANDMAYBE, and NOT. The guide demonstrates Spanish Y and O in place of English AND and OR, as well as symbolic operators.
The operator values are patterns, so escape regular-expression metacharacters when you want them treated literally. Replacing a token changes what users must type; make sure the interface’s help text and examples match the configured parser.
Opt in to fuzzy terms
FuzzyTermPlugin() enables forms such as cat~ and cat~2. The guide describes an edit distance of 1 by default and warns that distances above 2 can be very slow. That is qualitative guidance in the Whoosh documentation, not a benchmark for a particular index. Treat fuzzy matching—and especially higher distances—as an explicit product and performance choice.
Allow complex expressions in sequences
For more expressive contents inside a quoted or otherwise delimited sequence, the guide removes PhrasePlugin and adds SequencePlugin(). This changes what expressions are accepted in sequence syntax; its example also demonstrates slop, which allows distance between terms.
Build a custom operator when existing syntax is not enough
The Whoosh guide’s recipe for a custom operator is to choose whether it is prefix, postfix, or infix; define a GroupNode subclass that builds the corresponding query; write a regular expression for the syntax; create an OpTagger; and configure and install an OperatorsPlugin.
Infix operators are left-associative by default, and the order of operators affects binding strength. Define and test the intended precedence rather than assuming a new operator will group expressions the way users expect. The full version-specific walkthrough is in Whoosh’s parsing guide.
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There is no single best configuration: the right language depends on what users need to express and what the index can execute predictably.
- User-facing power: Decide whether users need field names, phrases, wildcards, fuzzy terms, or richer sequence expressions. Every enabled feature adds syntax they may need to learn.
- Performance and predictability: Consider restricting broad wildcard searches and treating fuzzy distances above 2 cautiously, in line with the guide’s qualitative warning.
- Discoverability and localization: Choose familiar English words, symbols, or application-specific operator terms, then keep in-product examples aligned with those choices.
- Schema fit and maintenance: Confirm that analyzers and positional data support the syntax you expose. A custom plugin can solve a genuine language need, but it also creates behavior your application must maintain and explain.
The cited documentation describes Whoosh 2.7.4. It does not establish current release status, Python compatibility, or package maintenance, so verify the API against the version used by your project before adopting an example.
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