Ok, in that case: why not use the standard Python syntax:
class Foo(...):
def _bar_if_cond(self):
....
def __init__(self, condition):
if condition: self.bar = self._bar_if_cond
Its still just one line to switch the method. IMHO decorators don't make it
particularly clear that the order matters. Of course it does, but its not a
syntax that lends itself to expressing interdependency.
Besides, we do already have a framework to switch out methods for an
instance: category refinement. And you can even do it at any time during
the life of the instance (e.g. when set_immutable is called).
On Thursday, August 22, 2013 10:50:35 PM UTC+1, Simon King wrote:
> Hi Volker,
>
> On 2013-08-22, Volker Braun <[email protected] <javascript:>> wrote:
> > I don't really like the way to express the condition in
> > @conditionally_defined, it breaks the Python idiom of explicitly passing
> > self. Whats the advantage of
> >
> > @conditionally_defined('cond')
> > def foo(self)
> > return ...
> >
> > over
> >
> > def foo(self):
> > if self.cond: return super(Class, self).foo()
> > return ...
>
> The former checks the condition exactly once per instance. The latter does
> the test and the super(...) call as often as foo() is called. In
> particular, if the condition is nontrivial to compute, it would be quite
> noticeable.
>
> With the latter idiom, it would be difficult to obtain that self.foo is
> cached if and *only* if the condition holds. Namely, doing
> @cached_method
> def foo(self):
> if not self.cond: return super(Class, self).foo()
> return ...
> would mean: self.foo() is cached even if the condition does not hold and
> super(Class, self).foo() is not cached. But doing
> @conditionally_defined(lambda x: x.cond)
> @cached_method
> def foo(self):
> return ...
> would mean: self.foo() is only a cached method if self.cond holds,
> otherwise super(Class, self).foo() is called (without being cached).
>
> Anyway, I guess Nicolas can tell more about its uses in MuPad.
>
> Cheers,
> Simon
>
>
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