Message269389
In the documentation for the `typing` module, the [entry for the `List` type][0] uses the following example to help demonstrate when to use `Sequence` vs `List`:
T = TypeVar('T', int, float)
def vec2(x: T, y: T) -> List[T]:
return [x, y]
def slice__to_4(vector: Sequence[T]) -> List[T]:
return vector[0:4]
However, the `slice__to_4` function does not actually typecheck since there's no guarantee that a slice of a sequence will return a `List`. For example the vector could be a numpy array or a custom subclass of `collections.abc.Sequence` with an unusual `__getitem__`. (Mypy correctly catches this error and complains about an "Incompatible return value type").
The documentation should probably be updated to use an example that _does_ typecheck, though I'm not sure what exactly that example might look like? Maybe replace `slice__to_4` with something like this?
def keep_positives(vector: Sequence[T]) -> List[T]:
return [item for item in vector if item > 0] |
|
Date |
User |
Action |
Args |
2016-06-27 17:09:40 | michael0x2a | set | recipients:
+ michael0x2a, docs@python |
2016-06-27 17:09:40 | michael0x2a | set | messageid: <1467047380.43.0.562730585486.issue27402@psf.upfronthosting.co.za> |
2016-06-27 17:09:40 | michael0x2a | link | issue27402 messages |
2016-06-27 17:09:39 | michael0x2a | create | |
|