Use generic type hints and new union syntax | with python 3.6+

If you just want to use new annotations for type checkers like mypy, then do not use this library and simply add from __future__ import annotations. But if you want to use those annotations at runtime, then you may be at the right place!

This library exposes:

• transform_annotation, which will transform list[str|int|float] into

  • typing.List[typing.Union[str, int, float]] for python 3.6 to 3.8
  • list[typing.Union[str, int, float]] for python 3.9 (since generic types are natively supported)

• a custom source code encoding future_typing that you can use to trigger the transformation at interpretation time

• a CLI to see the transformed source

    pip install future_typing

Just add this custom source code encoding at the top of your file

# -*- coding: future_typing -*-

and then use | and list[str], dict[str, int], ... as if you were using python 3.10

# -*- coding: future_typing -*-
from typing import Literal
class C:
    @staticmethod
    def g(t: tuple[int, ...]) -> tuple[int, ...]:
        return t
def f(a: list[str | int] | dict[str, str], b: Literal['pika'] | None = None) -> type[C]:
    x: set[str | int] = set(a)
    y: frozenset[str] = frozenset(['y1', 'y2'])
    t: tuple[int, ...] = (1, 2)
    print(f'it works! a: {a!r}, b: {b!r}')
    return C
f(['a', 'b', 1], 'pika')

$ python3.8 pika.py
it works! a: ['a', 'b'], b: 'pika'
$ mypy pika.py
Success: no issues found in 1 source file

$ future_typing pika.py
import typing as typing___
from typing import Literal
class C :
    @staticmethod
    def g (t :typing___.Tuple [int ,...])->typing___.Tuple [int ,...]:
        return t
def f (a :typing___.Union [typing___.List [typing___.Union [str ,int ]],typing___.Dict [str ,str ]],b :typing___.Union [Literal ['pika'],None ]=None )->typing___.Type [C ]:
    x :typing___.Set [typing___.Union [str ,int ]]=set (a )
    y :typing___.FrozenSet [str ]=frozenset (['y1','y2'])
    t :typing___.Tuple [int ,...]=(1 ,2 )
    print (f'it works! a: {a!r}, b: {b!r}')
    return C
f (['a','b',1 ],'pika')