I never really understood the importance of `Optional`. Often it can be left
out altogether and in other cases I find `Union[T, None]` more expressive
(explicit) than `Optional[T]` (+ the latter saves only 3 chars).
Especially for people not familiar with typing, the meaning of `Optional` is
not obvious at first sight. `Union[T, None]` on the other hand is pretty clear.
Also in other cases, where the default (fallback) is different from `None`,
you'd have to use `Union` anyway. For example a function that normally returns
an object of type `T` but in some circumstances it cannot and then it returns
the reason as a `str`, i.e. `-> Union[T, str]`; `Optional` won't help here.
Scanning through the docs and PEP I can't find strongly motivating examples for
`Optional` (over `Union[T, None]`). E.g. in the following:
def lookup(self, name: str) -> Optional[Node]:
nodes = self.get(name)
if nodes:
return nodes[-1]
return None
I would rather write `Union[Node, None]` because that's much more explicit
about what happens.
Then introducing `~T` in place of `Optional[T]` just further obfuscates the
meaning of the code:
def lookup(self, name: str) -> ~Node:
The `~` is easy to be missed (at least by human readers) and the meaning not
obvious.
For `Union` on the other hand it would be more helpful to have a shorter
syntax, `int | str` seems pretty clear, but what prevents tuples `(int, str)`
from being interpreted as unions by type checkers. This doesn't require any
changes to the built-in types and it is aligned with the already existing
syntax for checking multiple types with `isinstance` or `issubclass`:
`isinstance(x, (int, str))`. Having used this a couple of times, whenever I see
a tuple of types I immediately think of them as `or` options.
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