In the example I was aiming for something easy to understand that produced a
type illustrating potential problems of PEP 677, which is at its worst when
there are callables in both argument and return position. I don't have a great
real-world example of this worst-case, most of what I've seen involves simpler
and the current PEP 677 proposal isn't as bad.
As for formatting I agree that I wouldn't hand-write the type as
```
((int) -> float, (str) -> bool) -> (int, str) -> tuple[float, bool]
```
but a lot of code formatters might fight me on this, so I think it's worthy of
consideration, and I was trying to illustrate a readability problem and
possible fix. Formatting the code nicely so that my proposal looks good would
have meant not really engaging with the concern.
If you're looking for examples from real code where Callable is unweildy,
Pradeep collected a few at [1] from typeshed although most of them look just
fine with the current PEP 677 proposal. A couple examples:
Callable[[AnyStr, Callable[[AnyStr, AnyStr, AnyStr], AnyStr]], AnyStr]
Callable[[Optional[str], tuple[_Marshallable, ...]], Union[Fault,
tuple[_Marshallable, ...]]]
Callable[[str, Callable[[Iterable[str], str], str]], None]
versus the same types written using the current PEP 677 syntax:
(AnyStr, (AnyStr, AnyStr, AnyStr) -> AnyStr) -> AnyStr
(Optional[str], tuple[_Marshallable, ...]) -> Union[Fault, tuple[_Marshallable,
...]]
(str, (Iterable[str], str) -> str) -> None
versus with outer parentheses:
(AnyStr, (AnyStr, AnyStr, AnyStr -> AnyStr) -> AnyStr)
(Optional[str], tuple[_Marshallable, ...] -> Union[Fault, tuple[_Marshallable,
...]])
(str, (Iterable[str], str -> str) -> None)
and another idea, requiring both outer parentheses and argument parentheses:
((AnyStr, ((AnyStr, AnyStr, AnyStr )-> AnyStr)) -> AnyStr)
((Optional[str], tuple[_Marshallable, ...]) -> Union[Fault,
tuple[_Marshallable, ...]])
(str, (Iterable[str], str) -> str) -> None)
To me, these are convincing examples of where Callable is hard to read and an
arrow syntax is easier, but that doesn't necessarily mean it's worth the price
of new syntax.
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