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CPython implementation of intersections #9
Description
This is my stab at a reference implementation of the Intersection type in CPython:
https://github.com/tomasr8/cpython/tree/intersection-type
Contributions/improvements welcome!
Build instructions:
https://devguide.python.org/getting-started/setup-building/
TLDR:
git remote add tomasr8 https://github.com/tomasr8/cpython
git fetch tomasr8
git checkout --track tomasr8/intersection-type
make clean && make -s -j2
./pythonTODOs
- Intersection flattening (same as unions)
- fix some copy&paste errors - references to Union and UnionGenericAlias and some docstrings
- isinstance support
- Incorporate gh-105499: Merge typing.Union and types.UnionType python/cpython#105511 when it gets merged
Example
from typing import Intersection
Intersection[int, str]
Intersection[int, float, int] # == Intersection[int, float] (deduped)
Intersection[int, Intersection[float, str]] # == Intersection[int, float, str] (flattened)
Intersection[int] # == int
# overloaded __and__ for types
int & str
type(int & str)
class T: ...
T & int
class A: ...
class B: ...
class C(A, B): ...
a = A()
c = C()
isinstance(a, A & B)
isinstance(c, A & B)Reacted by Andrew, Jun Komoda, XieJiSS and Jeff May
Activity
NeilGirdhar commentedon Jul 28, 2023
Why create the
Intersectionname at all only to deprecate it immediately?Uniononly exists because|wasn't available.CarliJoy commentedon Jul 28, 2023
Because we can backport
Intersectionwithtyping_extensionsmaking it available also to older python versions.The
&will be only available with a newer Python version and nobody wants to way 2 Years for that...Also some people will be forced to use older version for quite some time and we need backwards compatibility for them.
NeilGirdhar commentedon Jul 28, 2023
Right, good point. BTW, you can still use
&in annotations by usingfrom __future__ import annotations, but I could see wanting to programmatically generate types.NeilGirdhar commentedon Jul 28, 2023
Also,
Intersectionshould probably not be added to Python—just to typing-extensions.Gobot1234 commentedon Jul 31, 2023
Strongly disagree with this.
typing_extensionsis meant to be for backportingtypingfeatures, not having it intypingwould create confusion.NeilGirdhar commentedon Jul 31, 2023
Good point. I guess as long as the linters push back, that's enough to discourage unnecessary use of it.
JelleZijlstra commentedon Sep 7, 2023
Late to the party here, but note that there is precedent for adding something to typing that is immediately sort-of-deprecated: PEP 646 added
typing.Unpackso that we could addtyping_extensions.Unpackwhile also adding new syntax that made it unnecessary to ever usetyping.Unpack. Analogously we could add atyping.Intersectionwhile simultaneously adding a&operator that means you (almost) never have to usetyping.Intersectiondirectly.tomasr8 commentedon Dec 14, 2023
Just an FYI, I rebased this on the latest CPython main