range() is not the best way to check range?

[Steve Holden]

Paul Boddie wrote:
[...]
> Regardless of whether myslice inherits from object or not, there's no
> persuading the interpreter that it is a genuine slice, and remember
> that we can't subclass slice (for some reason unknown). So, it would
> appear that the interpreter really wants instances from some specific
> set of types (presumably discoverable by looking at list_subscript in
> listobject.c) rather than some objects conforming to some interface or
> protocol, and perhaps it is implemented this way for performance
> reasons.
> 
> In any case, in the core of Python some types/classes are more equal
> than others, and for whatever reason the duck typing breaks down - a
> case of "malbik endar" [1] that you just have to be aware of, I
> suppose.
> 
  >>> class mySlice(types.SliceType):
  ...   pass
  ...
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: Error when calling the metaclass bases
     type 'slice' is not an acceptable base type
  >>>

Indeed.

regards
  Steve
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