typing.Union

class typing.Union

Union type; Union[X, Y] means either X or Y.

To define a union, use e.g. Union[int, str]. Details:

• The arguments must be types and there must be at least one.

• Unions of unions are flattened, e.g.:

  Union[Union[int, str], float] == Union[int, str, float]
  

• Unions of a single argument vanish, e.g.:

  Union[int] == int  # The constructor actually returns int
  

• Redundant arguments are skipped, e.g.:

  Union[int, str, int] == Union[int, str]
  

• When comparing unions, the argument order is ignored, e.g.:

  Union[int, str] == Union[str, int]
  

• If Any is present it is the sole survivor, e.g.:

  Union[int, Any] == Any
  

• You cannot subclass or instantiate a union.
• You cannot write Union[X][Y].
• You can use Optional[X] as a shorthand for Union[X, None].