apache_beam.typehints.typehints module

Syntax & semantics for type-hinting custom-functions/PTransforms in the SDK.

This module defines type-hinting objects and the corresponding syntax for type-hinting function arguments, function return types, or PTransform object themselves. TypeHint’s defined in the module can be used to implement either static or run-time type-checking in regular Python code.

Type-hints are defined by ‘indexing’ a type-parameter into a defined CompositeTypeHint instance:

  • ‘List[int]’.

Valid type-hints are partitioned into two categories: simple, and composite.

Simple type hints are type hints based on a subset of Python primitive types: int, bool, float, str, object, None, and bytes. No other primitive types are allowed.

Composite type-hints are reserved for hinting the types of container-like Python objects such as ‘list’. Composite type-hints can be parameterized by an inner simple or composite type-hint, using the ‘indexing’ syntax. In order to avoid conflicting with the namespace of the built-in container types, when specifying this category of type-hints, the first letter should capitalized. The following composite type-hints are permitted. NOTE: ‘T’ can be any of the type-hints listed or a simple Python type:

  • Any
  • Union[T, T, T]
  • Optional[T]
  • Tuple[T, T]
  • Tuple[T, ...]
  • List[T]
  • KV[T, T]
  • Dict[T, T]
  • Set[T]
  • Iterable[T]
  • Iterator[T]
  • Generator[T]

Type-hints can be nested, allowing one to define type-hints for complex types:

  • ‘List[Tuple[int, int, str]]

In addition, type-hints can be used to implement run-time type-checking via the ‘type_check’ method on each TypeConstraint.

class apache_beam.typehints.typehints.TypeVariable(name)[source]

Bases: apache_beam.typehints.typehints.AnyTypeConstraint


alias of WindowedTypeConstraint