get_args_and_origin

get_args_and_origin provides get_origin() and get_args() on Python < 3.8.

• On Python >= 3.8, it simply re-exports the stdlib implementations.
• On Python < 3.8, it backports equivalent behavior for the older typing constructs, plus typing_extensions.Annotated, typing_extensions.Final, and typing_extensions.Literal.

Installation

pip install get-args-and-origin

Usage

from get_args_and_origin import get_origin, get_args

Supported on Python < 3.8

Core typing constructs:

• List[T]
• Dict[K, V]
• Set[T]
• FrozenSet[T]
• Tuple[...]
• Callable[..., T]
• Callable[[A, B], R]
• Union[...]
• Optional[T]
• Type[T]
• nested generic aliases
• unsubscripted Generic

typing_extensions constructs:

• typing_extensions.Final[T]
• typing_extensions.Literal[...]
• typing_extensions.Annotated[T, ...]

Notes

• On Python < 3.8, Final, Literal, and Annotated should be used from typing_extensions, and get_origin() normalizes them to those typing_extensions objects.
• On Python >= 3.8, behavior is exactly whatever typing.get_origin() and typing.get_args() do in the standard library.
• Union argument ordering can vary slightly across old typing backports.

Quick assert-style smoke tests

These assert-style checks are meant to double as a compact, high-coverage compatibility suite for Python 2.7, 3.4, 3.5, 3.6, and 3.7.

from typing import (
    Callable,
    Dict,
    FrozenSet,
    Generic,
    List,
    Optional,
    Set,
    Tuple,
    Type,
    TypeVar,
    Union,
)
import typing_extensions
from get_args_and_origin import get_origin, get_args

T = TypeVar('T')
S = TypeVar('S')

assert get_origin(int) is None
assert get_origin(str) is None
assert get_args(int) == ()
assert get_args(str) == ()

assert get_origin(T) is None
assert get_args(T) == ()

assert get_origin(List[int]) is list
assert get_args(List[int]) == (int,)

assert get_origin(Dict[int, str]) is dict
assert get_args(Dict[int, str]) == (int, str)

assert get_origin(Set[int]) is set
assert get_args(Set[int]) == (int,)

assert get_origin(FrozenSet[int]) is frozenset
assert get_args(FrozenSet[int]) == (int,)

assert get_origin(Tuple[int, str]) is tuple
assert get_args(Tuple[int, str]) == (int, str)

assert get_origin(Tuple[int, ...]) is tuple
assert get_args(Tuple[int, ...]) == (int, Ellipsis)

assert get_origin(Union[int, str]) is Union
assert get_args(Union[int, str]) == (int, str)

assert get_origin(Optional[int]) is Union
assert get_args(Optional[int]) == (int, type(None))

assert get_origin(Callable[[int, str], bool]).__name__ == 'Callable'
assert get_args(Callable[[int, str], bool]) == ([int, str], bool)

assert get_origin(Callable[..., bool]).__name__ == 'Callable'
assert get_args(Callable[..., bool]) == (Ellipsis, bool)

assert get_origin(Type[int]) is type
assert get_args(Type[int]) == (int,)

assert get_origin(Generic) is Generic
assert get_args(Generic) == ()

assert get_origin(List) is list
assert get_origin(Dict) is dict
assert get_origin(Set) is set
assert get_origin(FrozenSet) is frozenset
assert get_origin(Tuple) is tuple
assert get_args(List) == ()
assert get_args(Dict) == ()
assert get_args(Set) == ()
assert get_args(FrozenSet) == ()

assert get_origin(Dict[str, List[Tuple[int, str]]]) is dict
assert get_args(Dict[str, List[Tuple[int, str]]]) == (str, List[Tuple[int, str]])

assert get_origin(List[Union[int, str]]) is list
assert get_args(List[Union[int, str]]) == (Union[int, str],)

assert get_origin(Dict[str, Optional[int]]) is dict
assert get_args(Dict[str, Optional[int]]) == (str, Optional[int])

assert get_origin(Tuple[List[int], Dict[str, bool]]) is tuple
assert get_args(Tuple[List[int], Dict[str, bool]]) == (List[int], Dict[str, bool])

assert get_origin(Tuple[List[T], Dict[str, S]]) is tuple
assert get_args(Tuple[List[T], Dict[str, S]]) == (List[T], Dict[str, S])

assert get_origin(Tuple[Union[int, str], Optional[bool]]) is tuple
assert get_args(Tuple[Union[int, str], Optional[bool]]) == (Union[int, str], Optional[bool])

Literal = typing_extensions.Literal
Final = typing_extensions.Final
Annotated = typing_extensions.Annotated

assert get_origin(Literal[1, 'x', True]) is Literal
assert get_args(Literal[1, 'x', True]) == (1, 'x', True)
assert get_origin(Literal[1]) is Literal
assert get_origin(Literal) is None
assert get_args(Literal) == ()

assert get_origin(Final[int]) is Final
assert get_args(Final[int]) == (int,)
assert get_origin(Final) is None
assert get_args(Final) == ()

assert get_origin(Annotated[int, 'm1', 'm2']) is Annotated
assert get_args(Annotated[int, 'm1', 'm2']) == (int, 'm1', 'm2')
assert get_origin(Annotated[int, 'm']) is Annotated
assert get_origin(Annotated[List[int], 'tag']) is Annotated
assert get_args(Annotated[List[int], 'tag']) == (List[int], 'tag')
assert get_origin(Annotated[Union[int, str], 'u']) is Annotated
assert get_args(Annotated[Union[int, str], 'u']) == (Union[int, str], 'u')

nested = Dict[
    str,
    Tuple[
        List[Optional[int]],
        Annotated[Literal[1, 2], 'meta'],
    ],
]
assert get_origin(nested) is dict
assert get_args(nested) == (
    str,
    Tuple[
        List[Optional[int]],
        Annotated[Literal[1, 2], 'meta'],
    ],
)

Contributing

Contributions are welcome! Please submit pull requests or open issues on the GitHub repository.

License

This project is licensed under the MIT License.