Ternary plus
in [Python]
|
Prev: Awful book warning: How to think like a (Python) programmer -non-working examples
Next: Read PGM's with more than 256 range in PIL1.1.7
From: Gabriel Genellina on 9 Feb 2010 18:59 En Tue, 09 Feb 2010 15:47:43 -0300, Martin Drautzburg <Martin.Drautzburg(a)web.de> escribi�: > Carl Banks wrote: > >> You can have __add__ return a closure for the first addition, then >> perform the operation on the second one. Example (untested): >> > > That's way cool. > > <Flash of insight> Of course! - CURRYING!! If you can return closures > you can do everything with just single-parameter functions.</Flash of > insight> > > BTW I am not really trying to add three objects, I wanted a third object > which controls the way the addition is done. Sort of like "/" and "//" > which are two different ways of doing division. See http://code.activestate.com/recipes/384122/ for another cool hack that may help with that. -- Gabriel Genellina
From: Mark Dickinson on 10 Feb 2010 03:31 On Feb 9, 6:47 pm, Martin Drautzburg <Martin.Drautzb...(a)web.de> wrote: > BTW I am not really trying to add three objects, I wanted a third object > which controls the way the addition is done. Sort of like "/" and "//" > which are two different ways of doing division. That seems like a reasonable use case for a third parameter to __add__, though as others have pointed out the only way to pass the third argument is to call __add__ explicitly. Here's an extract from the decimal module: class Decimal(object): ... def __add__(self, other, context=None): other = _convert_other(other) if other is NotImplemented: return other if context is None: context = getcontext() <add 'self' and 'other' in context 'context'> ... And here's how it's used in the decimal.Context module: class Context(object): ... def add(self, a, b): """Return the sum of the two operands. >>> ExtendedContext.add(Decimal('12'), Decimal('7.00')) Decimal('19.00') >>> ExtendedContext.add(Decimal('1E+2'), Decimal('1.01E+4')) Decimal('1.02E+4') """ return a.__add__(b, context=self) -- Mark
From: Mark Dickinson on 10 Feb 2010 03:42
On Feb 10, 8:31 am, Mark Dickinson <dicki...(a)gmail.com> wrote: > And here's how it's used in the decimal.Context module: Aargh! decimal.Context *class*, not module. And it occurs to me that it would have been cleaner to have Decimal.__add__ call Context.add rather than the other way around. Then Decimal.__add__ could have stayed a two-argument function, as <deity of your choice> intended. Oh well. -- Mark |