Two-Dimensional Expression Layout

[Lawrence D’Oliveiro]

On Sunday, August 21, 2016 at 12:44:21 PM UTC+12, Michael Selik wrote:
>
> On Sat, Aug 20, 2016 at 6:21 PM Lawrence D’Oliveiro wrote:
> 
>>>     if any(not isinstance(obj, Image) for obj in [src, mask, dest]):
>>>         ...
>>
>> Spot the bug in your version...
> 
> - ``mask != None`` is unnecessary, unless somehow None has been registered
> as an instance of Image.

That’s the bug: it’s not unnecessary.

Maybe a quick application of one of De Morgan’s theorems might help:

    if (
            isinstance(src, Image)
        and
            (mask == None or isinstance(mask, Image))
        and
            isinstance(dest, Image)
    ) :
        don’t raise TypeError("image args must be Image objects")
    #end if

Is that better for you?