On Mon, 15 Jan 2007 14:43:55 +1100, Steven D'Aprano wrote:
>> Of course, none of this really has anything to do with rational
>> numbers. There must be many examples of classes for which internal
>> calls to __init__, from other methods of the same class, require
>> minimal argument processing, while external calls require heavier and
>> possibly computationally expensive processing. What's the usual way
>> to solve this sort of problem?
>
> class Rational(object):
> def __init__(self, numerator, denominator):
> print "lots of heavy processing here..."
> # processing ints, floats, strings, special case arguments,
> # blah blah blah...
> self.numerator = numerator
> self.denominator = denominator
> def __copy__(self):
> cls = self.__class__
> obj = cls.__new__(cls)
> obj.numerator = self.numerator
> obj.denominator = self.denominator
> return obj
> def __neg__(self):
> obj = self.__copy__()
> obj.numerator *= -1
> return obj
Here's a variation on that which is perhaps better suited for objects with
lots of attributes:
def __copy__(self):
cls = self.__class__
obj = cls.__new__(cls)
obj.__dict__.update(self.__dict__) # copy everything quickly
return obj
--
Steven D'Aprano
--
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