Issue Type
quicktype output (generated code cannot be used) / test coverage gap
Context (Environment, Version, Language)
Input Format:
JSON Schema
Output Language:
Python
CLI, npm, or app.quicktype.io:
CLI (also reproducible via npm package)
Version:
Current master (also present historically — this is a longstanding, still-unfixed gap)
Description
test/inputs/schema/keyword-unions.schema is a flat object with 276 properties, each a oneOf union. Generating Python from it produces a constructor call with one argument per property — 276 arguments — which exceeds CPython's hard limit of 255 arguments per call. As a result, this fixture is permanently skipped for Python:
// test/languages.ts
skipSchema: [
"keyword-unions.schema", // Requires more than 255 arguments
],This isn't just a test-suite inconvenience — it means quicktype can generate genuinely broken Python for any real-world schema wide enough to trip the same limit, and there's no test coverage to catch a regression or confirm a fix.
Input Data
test/inputs/schema/keyword-unions.schema — 276 properties, each shaped:
"constructor": {
"oneOf": [
{ "type": "number" },
{ "type": "object", "additionalProperties": false, "title": "constructor" }
],
"title": "union_constructor"
}
(276 properties like this, plus a trailing "dummy": {"type": "number"}.)
Expected Behaviour / Output
Generated Python for a wide object should produce valid, importable Python regardless of property count — e.g. by constructing instances via **kwargs / a dict rather than one positional argument per property, or by grouping fields.
Current Behaviour / Output
Generation succeeds, but the resulting Python is unusable — the generated init/constructor call exceeds CPython's 255-argument ceiling and raises SyntaxError: more than 255 arguments (or an equivalent error) at import/call time. Confirmed via node dist/index.js --lang python --src-lang schema test/inputs/schema/keyword-unions.schema — the widest generated call site is 276 arguments.
Steps to Reproduce
- npm run build
- node dist/index.js --lang python --src-lang schema test/inputs/schema/keyword-unions.schema
- Attempt to import/exercise the generated Python module
- Observe the argument-count error
Possible Solution
Grouping the schema's properties into smaller nested objects (e.g. 5 groups of ~56) drops the widest call site well under 255 and would let this fixture run for Python — verified locally as part of investigating #559 (unrelated issue, same fixture). That's a workaround for this schema, not a general fix: quicktype's Python renderer arguably shouldn't emit an N-argument call for arbitrarily wide objects in the first place. Worth deciding whether the fix belongs in the renderer (structural) or is accepted as an input-shape limitation (documented).
Issue Type
quicktype output (generated code cannot be used) / test coverage gap
Context (Environment, Version, Language)
Input Format:
JSON Schema
Output Language:
Python
CLI, npm, or app.quicktype.io:
CLI (also reproducible via npm package)
Version:
Current master (also present historically — this is a longstanding, still-unfixed gap)
Description
test/inputs/schema/keyword-unions.schemais a flat object with 276 properties, each aoneOfunion. Generating Python from it produces a constructor call with one argument per property — 276 arguments — which exceeds CPython's hard limit of 255 arguments per call. As a result, this fixture is permanently skipped for Python:This isn't just a test-suite inconvenience — it means quicktype can generate genuinely broken Python for any real-world schema wide enough to trip the same limit, and there's no test coverage to catch a regression or confirm a fix.
Input Data
(276 properties like this, plus a trailing "dummy": {"type": "number"}.)
Expected Behaviour / Output
Generated Python for a wide object should produce valid, importable Python regardless of property count — e.g. by constructing instances via **kwargs / a dict rather than one positional argument per property, or by grouping fields.
Current Behaviour / Output
Generation succeeds, but the resulting Python is unusable — the generated init/constructor call exceeds CPython's 255-argument ceiling and raises SyntaxError: more than 255 arguments (or an equivalent error) at import/call time. Confirmed via node dist/index.js --lang python --src-lang schema test/inputs/schema/keyword-unions.schema — the widest generated call site is 276 arguments.
Steps to Reproduce
Possible Solution
Grouping the schema's properties into smaller nested objects (e.g. 5 groups of ~56) drops the widest call site well under 255 and would let this fixture run for Python — verified locally as part of investigating #559 (unrelated issue, same fixture). That's a workaround for this schema, not a general fix: quicktype's Python renderer arguably shouldn't emit an N-argument call for arbitrarily wide objects in the first place. Worth deciding whether the fix belongs in the renderer (structural) or is accepted as an input-shape limitation (documented).