11.3. Dataclass Define Special¶
11.3.1. Literal Field¶
>>> from dataclasses import dataclass, field
>>> from typing import Literal
>>>
>>>
>>> @dataclass
... class Astronaut:
... firstname: str
... lastname: str
... agency: Literal['NASA', 'ESA', 'Roscosmos']
11.3.2. Union Fields¶
>>> from dataclasses import dataclass
>>>
>>>
>>> @dataclass
... class Astronaut:
... firstname: str
... lastname: str
... age: int | float
11.3.3. Optional Fields¶
>>> from dataclasses import dataclass
>>>
>>>
>>> @dataclass
... class Astronaut:
... firstname: str
... lastname: str
... agency: str | None = None
11.3.4. Final Fields¶
In Python there is no constants
>>> from dataclasses import dataclass
>>> from typing import Final
>>>
>>>
>>> @dataclass
... class Astronaut:
... firstname: str
... lastname: str
... age: int
... AGE_MIN: Final[int] = 30
... AGE_MAX: Final[int] = 50
11.3.5. KWargs Only¶
Any fields after a pseudo-field with the type of KW_ONLY are marked as keyword-only fields. Note that a pseudo-field of type KW_ONLY is otherwise completely ignored. This includes the name of such a field. By convention, a name of _ is used for a KW_ONLY field.
>>> from dataclasses import dataclass, KW_ONLY
>>>
>>>
>>> @dataclass
... class Astronaut:
... firstname: str
... lastname: str
... _: KW_ONLY
... age: int
... height: float
... weight: float