Richard D. Moores wrote:
> On Tue, Aug 28, 2012 at 1:21 AM, Timo <timomli...@gmail.com> wrote:
>> Op 28-08-12 10:06, Richard D. Moores schreef:
>
>>> What if I wanted 3., 1234., etc. to be considered ints, as they are by
>>> _validate_int() ?
>>
>>
>>>>> isinstance(3., (int, float))
>> True
>>
>> Because 3. is a float, not int.
>
> And
>>>> isinstance(3.7, (int, float))
> True
>
> No, I'm asking for something equivalent to _validate_int().
That's not how it works. You have to give a spec first and then you can
compare how well it is met by a particular implementation. If you start with
an implementation and then declare its behaviour to be the spec the
implementation will always "win". That's why ISO 29500 works so well -- for
the company that wrote it.
Anyway here's an alternative implementation:
>>> def vi(x):
... if not isinstance(x, numbers.Number):
... raise TypeError
... if not int(x) == x:
... raise ValueError
...
>>> vi("")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 3, in vi
TypeError
>>> vi(1.5)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 5, in vi
ValueError
>>> vi(1.0)
>>>
The differences to _validate_int() are subtle:
>>> class S(str):
... def __eq__(self, other): return True
... def __ne__(self, other): return False
... def __add__(self, other): return self
...
>>> vi(S("42"))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 3, in vi
TypeError
>>> _validate_int(S("42"))
>>>
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