I read PEP 604 (Complementary syntax for Union []).

When I heard that Microsoft's checker for Python pyright supports the latest specifications and scanned the README, I hadn't watched it before. PEP 604 (Complementary syntax for Union []) was listed, so I took a look. By the way, I will write about PEP-612 in the next article.

Overview

• Isn't it annoying to write ʻUnion [int, str]` every time?
• Let's write ʻint | str` like Scala
• Let's use not only type annotation but also ʻisinstance () and ʻissubclass ()

approach

• Make it possible to create a type set by connecting types with |

that's all.

Example

The sample in PEP is self-explanatory, so I won't explain it.

# in place of
# def f(list: List[Union[int, str]], param: Optional[int]) -> Union[float, str]
def f(list: List[int | str], param: int | None) -> float | str:
    pass

f([1, "abc"], None)

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

assert isinstance("", int | str)
assert issubclass(bool, int | float)

Impressions

• Honestly, it ’s not good ...
• It doesn't look too strange when you see it in Scala, but when you look at it as Python, it's just that you're just not used to it.
• Writing Union is easier, but writing List [int | str] isn't very beneficial ...
• Since it is Draft yet, adoption has not been decided yet