OpenAPITools/openapi-generator · error · IllegalArgumentException

mapNumberTo supports %s

Error message

mapNumberTo supports %s

What it means

Thrown by setMapNumberTo in AbstractPythonCodegen, the base for the modern Python generators (python, python-fastapi, etc.). The mapNumberTo option selects which Python type OpenAPI 'number' properties map to, and only the strings in SUPPORTED_NUMBER_MAPPINGS are accepted: 'Union[StrictFloat, StrictInt]', 'StrictFloat', 'float', 'Decimal'. Any other string fails with this IllegalArgumentException; the message interpolates the exact allowed set.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractPythonCodegen.java:1241

                                       PythonImports moduleImports,
                                       String classname) {
        PydanticType pt = new PydanticType(
                modelImports,
                exampleImports,
                postponedModelImports,
                postponedExampleImports,
                moduleImports,
                classname
        );

        return pt.getType(cp);
    }

    public void setMapNumberTo(String mapNumberTo) {
        if (SUPPORTED_NUMBER_MAPPINGS.contains(mapNumberTo)) {
            this.mapNumberTo = mapNumberTo;
        } else {
            throw new IllegalArgumentException(String.format(Locale.ROOT, "mapNumberTo supports %s", SUPPORTED_NUMBER_MAPPINGS));
        }
    }

    public String toEnumVariableName(String name, String datatype) {
        name = name.replace(".", "_DOT_");

        if ("int".equals(datatype)) {
            return "NUMBER_" + name.replace("-", "MINUS_");
        }

        // remove quote e.g. 'abc' => abc
        if (name.startsWith("'") && name.endsWith("'")) {
            name = name.substring(1, name.length() - 1);
        }

        if (name.length() == 0) {
            return "EMPTY";
        }

View on GitHub (pinned to fcec517be3)

Solutions

  1. Re-run with an exact allowed value: -p mapNumberTo=float (the default), StrictFloat, Decimal, or Union[StrictFloat, StrictInt]
  2. Remove the option entirely and accept the generator default while you verify the spelling
  3. If you need pydantic strict types such as StrictStr, switch to the pydantic-v1 based generator (e.g. -g python-pydantic-v1) where that value is accepted
  4. Check for case sensitivity, exact brackets and commas — the check is an exact Set.contains string comparison

Example fix

# before
java -jar openapi-generator-cli.jar generate -g python -i api.yaml -p mapNumberTo=StrictStr

# after
java -jar openapi-generator-cli.jar generate -g python -i api.yaml -p mapNumberTo=Union[StrictFloat, StrictInt]
Defensive patterns

Strategy: validation

Validate before calling

// Java (before calling the generator)
Set<String> allowed = Set.of("Union[StrictFloat, StrictInt]", "StrictFloat", "float", "Decimal");
String v = (String) config.additionalProperties().get("mapNumberTo");
if (v != null && !allowed.contains(v)) {
    throw new IllegalArgumentException("mapNumberTo must be one of " + allowed + ", got: " + v);
}

Try / catch

try { generator.generate(); } catch (IllegalArgumentException e) { if (e.getMessage().startsWith("mapNumberTo supports")) { /* config error: fix the option value, do not retry */ } throw e; }

Prevention

When it happens

Trigger: Running a Python-family generator with -p mapNumberTo=<value> (or additionalProperties in the Maven/Gradle plugin) where <value> is not byte-for-byte one of the four allowed strings: mapNumberTo=StrictStr, mapNumberTo=decimal (lowercase), mapNumberTo=Decimal on an old release before Decimal was added, or 'Union[StrictFloat, StrictInt]' with stray whitespace or smart quotes.

Common situations: Copying mapNumberTo=StrictStr from pydantic-v1 generator examples (valid there, rejected by this codegen); case/bracket typos in the Union value; upgrading or downgrading generator versions where the accepted set differed.

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/1d00687c49cba42b. Report an issue: GitHub.