SV: Polymorphism using constructors

K Viltersten tmp1 at viltersten.com
Tue Mar 4 21:00:23 CET 2008


"Carl Banks" <pavlovevidence at gmail.com> skrev i meddelandet 
news:24adaf72-0c55-4a88-86d0-296363ead17f at s8g2000prg.googlegroups.com...
> On Mar 3, 4:17 pm, Raymond Hettinger <pyt... at rcn.com> wrote:
>> Since Python doesn't support having two methods with the same name,
>> the usual solution is to provide alternative constructors using
>> classmethod():
>>
>>   @classmethod
>>   def from_decimal(cls, d)
>>         sign, digits, exp = d.as_tuple()
>>         digits = int(''.join(map(str, digits)))
>>         if sign:
>>             digits = -digits
>>         if exp >= 0:
>>             return cls(digits * 10 ** exp)
>>         return cls(digits, 10 ** -exp)
>
>
> Note that even some of Python's built in types (dict *cough*)
> implement homemade function overloading.
>
> The OP wanted to write a constructor that could accept either a pair
> of integers or a rational, there would be a good precedent for it.
>
> However, I would advise the OP to use the constructor only for the
> most common arguments, and use classmethods for more obscure, less
> common arguments (such as decimal or even float).


OP understands and thanfully accepts
the suggestion.

--
Regards
Konrad Viltersten
--------------------------------
sleep    - a substitute for coffee for the poor
ambition - lack of sense to be lazy




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