{"record":{"id":"afa6ef5278ee1ef4","repo":"pathwaycom/pathway","slug":"index-expression-const-index-out-of-range-for-a","errorCode":null,"errorMessage":"Index {expression._const_index} out of range for a tuple of type {object_dtype.typehint}.","messagePattern":"Index (.+?) out of range for a tuple of type (.+?)\\.","errorType":"exception","errorClass":"IndexError","httpStatus":null,"severity":"error","filePath":"python/pathway/internals/type_interpreter.py","lineNumber":590,"sourceCode":"            try:\n                try_ret = dtypes[expression._const_index]\n                return _wrap(expression, try_ret)\n            except IndexError:\n                message = (\n                    f\"Index {expression._const_index} out of range for a tuple of\"\n                    + f\" type {object_dtype.typehint}.\"\n                )\n                if expression._check_if_exists:\n                    expression_info = get_expression_info(expression)\n                    warnings.warn(\n                        message\n                        + \" It refers to the following expression:\\n\"\n                        + expression_info\n                        + \"Consider using just the default value without .get().\"\n                    )\n                    return _wrap(expression, default_dtype)\n                else:\n                    raise IndexError(message)\n\n    def eval_method_call(\n        self,\n        expression: expr.MethodCallExpression,\n        state: TypeInterpreterState | None = None,\n        **kwargs,\n    ) -> expr.MethodCallExpression:\n        expression = super().eval_method_call(expression, state=state, **kwargs)\n        dtypes = tuple([arg._dtype for arg in expression._args])\n        if (dtypes_and_handler := expression.get_function(dtypes)) is not None:\n            return _wrap(expression, dt.wrap(dtypes_and_handler[1]))\n\n        if len(dtypes) > 0:\n            with_arguments = (\n                f\" with arguments of type {[dtype.typehint for dtype in dtypes[1:]]}\"\n            )\n        else:\n            with_arguments = \"\"","sourceCodeStart":572,"sourceCodeEnd":608,"githubUrl":"https://github.com/pathwaycom/pathway/blob/fa2f74a4649b7c5908690cf60137263d8d80de5f/python/pathway/internals/type_interpreter.py#L572-L608","documentation":"Raised when a constant int index is out of range for a Tuple-typed column. The interpreter looks up dtypes[const_index]; on IndexError it emits either a warning (if .get() with a default was used, telling you the tuple type can never contain that index so the default will always be returned) or raises this IndexError for plain access.","triggerScenarios":"t.tuple_col.get(5) where the column is Tuple[int, str] (valid indices 0..1); t.tup[3] with a 2-element tuple type. With .get() it degrades to a UserWarning suggesting to drop .get() and use the default directly; without .get() it raises.","commonSituations":"Schema tuple length changed (fewer elements) and old index now out of range; off-by-one in index; index computed from user config exceeding tuple length; developer expects runtime-length tuples but schema declares a fixed-length Tuple.","solutions":["Use an index within the declared tuple length (0 .. len-1)","Update the schema if the data actually has more elements: Tuple[int, str, float]","If tuple length varies per row, use pw.Json or a List type and dynamic int access instead of Tuple","If you used .get(default), heed the warning: the default will always be returned, so replace tup.get(5, default) with just default"],"exampleFix":"// before\nschema = pw.schema_from_types(tup=pw.Tuple[int, str])\nres = t.select(x=t.tup.get(5, 0))\n\n// after\nschema = pw.schema_from_types(tup=pw.Tuple[int, str, float, int, int, int])\nres = t.select(x=t.tup.get(5, 0))","handlingStrategy":"validation","validationCode":"from pathway.internals import dtype as dt\n\ndef tuple_index_ok(tuple_dtype, n: int) -> bool:\n    return isinstance(tuple_dtype, dt.Tuple) and 0 <= n < len(tuple_dtype.args)","typeGuard":"from pathway.internals import dtype as dt\n\ndef is_in_range_tuple(tuple_dtype, n: int) -> bool:\n    return isinstance(tuple_dtype, dt.Tuple) and 0 <= n < len(tuple_dtype.args)","tryCatchPattern":"try:\n    v = t.tup[5]\nexcept IndexError as e:\n    if 'out of range for a tuple' in str(e):\n        v = DEFAULT  # or fix the schema\n    else:\n        raise","preventionTips":["Keep tuple schema length in sync with the indices used in code","Treat the .get() UserWarning about always-default as a schema bug, not noise","Prefer pw.Json or pw.List when tuple length varies across rows"],"tags":["pathway","types","tuple","indexing","schema"],"backgroundTag":null,"analyzedSha":"fa2f74a4649b7c5908690cf60137263d8d80de5f","analyzedAt":"2026-08-15T01:48:17.006Z","schemaVersion":2},"datasetVersion":"2026-08-15T22:17:37.221Z"}