Two-Dimensional Expression Layout

Sun Aug 21 00:26:08 EDT 2016

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?