{"record":{"id":"86e29666a45d2be1","repo":"apache/beam","slug":"failed-to-convert-beam-type-s","errorCode":null,"errorMessage":"Failed to convert Beam type: %s","messagePattern":"Failed to convert Beam type: (.+?)","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"sdks/python/apache_beam/typehints/native_type_compatibility.py","lineNumber":633,"sourceCode":"      return typing.Any\n    return typing.Union[tuple(convert_to_python_types(typ.union_types))]\n  if isinstance(typ, typehints.SetTypeConstraint):\n    return set[convert_to_python_type(typ.inner_type)]\n  if isinstance(typ, typehints.FrozenSetTypeConstraint):\n    return frozenset[convert_to_python_type(typ.inner_type)]\n  if isinstance(typ, typehints.TupleConstraint):\n    return tuple[tuple(convert_to_python_types(typ.tuple_types))]\n  if isinstance(typ, typehints.TupleSequenceConstraint):\n    return tuple[convert_to_python_type(typ.inner_type), ...]\n  if isinstance(typ, typehints.ABCSequenceTypeConstraint):\n    return collections.abc.Sequence[convert_to_python_type(typ.inner_type)]\n  if isinstance(typ, typehints.IteratorTypeConstraint):\n    return collections.abc.Iterator[convert_to_python_type(typ.yielded_type)]\n  if isinstance(typ, typehints.MappingTypeConstraint):\n    return collections.abc.Mapping[convert_to_python_type(typ.key_type),\n                                   convert_to_python_type(typ.value_type)]\n\n  raise ValueError('Failed to convert Beam type: %s' % typ)\n\n\ndef convert_to_python_types(args):\n  \"\"\"Convert the given list or dictionary of args to python types.\n\n  Args:\n    args: Either an iterable of types, or a dictionary where the values are\n    types.\n\n  Returns:\n    If given an iterable, a list of converted types. If given a dictionary,\n    a dictionary with the same keys, and values which have been converted.\n  \"\"\"\n  if isinstance(args, dict):\n    return {k: convert_to_python_type(v) for k, v in args.items()}\n  else:\n    return [convert_to_python_type(v) for v in args]\n","sourceCodeStart":615,"sourceCodeEnd":651,"githubUrl":"https://github.com/apache/beam/blob/12126d8942aaf848030c478b4c6a28c6af861c66/sdks/python/apache_beam/typehints/native_type_compatibility.py#L615-L651","documentation":"convert_to_python_type converts internal Beam type-hint constraint objects (e.g. TypeVariable constraints, IterableTypeConstraint) back to native Python typing constructs. It raises ValueError when it receives a Beam type it has no conversion branch for. This indicates an unsupported or unexpected Beam type hint object was passed in.","triggerScenarios":"Calling convert_to_python_type or convert_to_python_types with a Beam typehints constraint class not handled by the isinstance chain (e.g. a custom or newly-added Beam constraint), or via to_runner_api_parameter when serializing a PCollection whose type hint is unsupported.","commonSituations":"Writing a custom runner or pipeline fragment serialization that round-trips type hints; using exotic Beam type constraints (e.g. SetTypeConstraint variants) in coders/runner-api conversion; upgrading Beam so new constraint types appear in old converters.","solutions":["Inspect the Beam type object passed in (print(type(typ))) and use a supported equivalent (e.g. IterableTypeConstraint instead of a custom constraint).","Add a conversion branch for the new constraint type in native_type_compatibility.convert_to_python_type.","Catch ValueError and fall back to typehints.Any when exact round-tripping is not required.","Verify both sides of the serialization run the same Beam version so constraint classes match."],"exampleFix":"// before\npy_type = convert_to_python_type(my_custom_constraint)  # ValueError\n// after\ntry:\n    py_type = convert_to_python_type(my_custom_constraint)\nexcept ValueError:\n    py_type = typing.Any  # fallback","handlingStrategy":"try-catch","validationCode":"from apache_beam.typehints import typehints\nSUPPORTED = (typehints.IterableTypeConstraint, typehints.MapTypeConstraint)\ndef is_convertible_beam_type(typ) -> bool:\n    return isinstance(typ, SUPPORTED + tuple(typehints.__all__ and [])) or hasattr(typehints, type(typ).__name__)\n","typeGuard":"def is_beam_constraint(typ) -> bool:\n    from apache_beam.typehints import typehints\n    return isinstance(typ, typehints.TypeConstraint)\n","tryCatchPattern":"try:\n    py_type = convert_to_python_type(beam_type)\nexcept ValueError:\n    py_type = typing.Any  # degrade gracefully instead of failing serialization\n","preventionTips":["Only round-trip Beam types produced by convert_to_beam_type, not hand-built constraints.","Keep both sides of a serialization boundary on the same Beam version.","Avoid exotic/legacy constraint types in pipeline definitions.","Log the repr of failed types to identify unsupported constraints early."],"tags":["python","apache-beam","type-hints"],"backgroundTag":"unsupported-operation","analyzedSha":"12126d8942aaf848030c478b4c6a28c6af861c66","analyzedAt":"2026-09-13T01:50:10.254Z","contentChangedAt":"2026-09-13T01:50:10.254Z","schemaVersion":2},"datasetVersion":"2026-09-20T03:17:13.778Z"}