On 04/03/2013 12:21 PM, Tres Seaver wrote:
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On 04/03/2013 01:50 PM, Ethan Furman wrote:
On 04/03/2013 10:46 AM, Barry Warsaw wrote:
On Apr 04, 2013, at 03:04 AM, Steven D'Aprano wrote:
On 04/04/13 01:16, Barry Warsaw wrote:
the other built-in types-as-functions, so int() calls __int__()
which must return a concrete integer.
Why must it? I think that's the claim which must be justified, not
just taken as a given. When we call n = int(something), what's
the use-case for caring that n is an instance of built-in int but
not of a subclass, and is that use-case so compelling that it must
be enforced for all uses of int() etc.?
It's a consistency-of-implementation issue. Where built-in types
are callable, they return concrete instances of themselves. This is
true for e.g. list, tuple, dict, bytes, str, and should also be true
of int.
Given that requirement, we still don't have to mandate that __int__
return an actual instance of the int type: the coercion could happen
inside int() (as it would for any non-subclass).
I don't understand. A non-int could only become an int via __int__, which int() calls. What magic is there in int() to
turn any arbitrary object into an integer?
--> class NonInt():
... def __str__(self):
... return "Not an integer!"
...
--> ni = NonInt()
--> ni
<__main__.NonInt object at 0x267a090>
--> str(ni)
'Not an integer!'
--> int(ni)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: int() argument must be a string or a number, not 'NonInt'
--
~Ethan~
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