On Thu, 05 Jul 2018 13:54:28 +0200, Antoon Pardon wrote:
> On 05-07-18 11:59, Steven D'Aprano wrote:
>> On Thu, 05 Jul 2018 17:34:55 +1200, Gregory Ewing wrote:
>>
>>
>>>> Indeed, that's often the best way, except for the redundant type
>>>> hint, which makes you That Guy:
>>>>
>>>> x: int = 0 # set x to the int 0
>>> But you've shown in an earlier example that such a hint is *not*
>>> always redundant
>> But it is redundant in *that* example. Your hint is not giving any more
>> information that what the reader, or type checker, can already infer.
>
> Yes it gives more information. Without the hint you can only interfere
> that it is an int at that point.
That would be utterly pointless:
x = 3 # infer x must be an int, but only at this point
y = x + "Hello world" # who knows what x is now? maybe it's okay
A type checker that did that would be a waste of time.
> IIUC, with the hint you can interfere
> it is supposed to be an int during its life time, not just at that
> point.
No.
Mypy considers the initial assignment as the definition
of a variable. If you do not explicitly specify the type
of the variable, mypy infers the type based on the
static type of the value expression
http://mypy.readthedocs.io/en/latest/type_inference_and_annotations.html
This is not an innovation of Mypy. It's how type inference is supposed to
work. If a particular type checker doesn't do that, it is doing it wrong.
--
Steven D'Aprano
"Ever since I learned about confirmation bias, I've been seeing
it everywhere." -- Jon Ronson
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