On Sat, 10 Feb 2007 07:55:54 -0500
Kent Johnson <[EMAIL PROTECTED]> wrote:
> thomas coopman wrote:
> > Hi,
> >
> > I want to do something like this, don't know how to properly
> > explain it, so I just give you some example code
> >
> >>>> class Foo(object):
> >>>> def method(self, arg):
> >>>> print arg
> >
> >>>> def doSomething(object, func):
> >>>> object.func("test")
> >
> >>>> object = Foo()
> >>>> doSomething(object, Foo.method)
> >
> > I want to execute the class method given as argument,
> > but this obvious doesn't work, but I don't know how to
> > get it work,
>
> First a quick note - don't use object as a parameter or variable
> name, it will hide the definition of the built-in object class.
Yes, I know, it was a bad example
>
> You are very close. Foo.method is called an 'unbound method' of class
> Foo. The syntax for calling an unbound method is to pass a class
> instance as the first argument, followed by the actual argument list.
> It is actually the same argument list that you use when you declare
> the function (starting with self).
>
> So your example can be written this way:
>
> In [4]: class Foo(object):
> ...: def method(self, arg):
> ...: print arg
>
> In [6]: o=Foo()
>
> In [8]: def doSomething(obj, func):
> ...: func(obj, "test")
>
> In [9]: doSomething(o, Foo.method)
> test
>
>
> A more common way to do this is to use a 'bound method'. That is what
> you get when you refer to instance.method instead of Class.method. A
> bound method includes a reference to the particular instance and can
> be called like an ordinary function. Rather than passing the instance
> and the unbound method to doSomething(), just pass the bound method
> as a single argument:
>
> In [10]: def doSomething(func):
> ....: func("test")
>
> In [12]: doSomething(o.method)
> test
>
> In summary:
> Class.method => unbound method, call with instance as first arg
> instance.method => bound method, call with normal argument list
>
> Kent
>
Thank you for the explanation of bound and unbound methods.
I understand that it is more common to use a bound method, but I don't
think that I can use this because at the time I save the method, I don't
know anything about the instances.
I use this for making a sorted list using any method you give as
argument when you create the list. This class only gets to know it's
instances when you add them.
In [3]: class SortedList(object):
...: def __init__(self, compare):
...: self.compare = compare
...: def __add_(self, object):
...: for i in self.data:
...: self.compare(object, i)
...:
In [4]: class FooList(SortedList):
...: def __init__(self):
...: self.compare = Foo.compare
__add__ doesn't do anything here of course, it is just an example,
but I don't think that I can use a bound method in this case?
also,
Is it better to use super in FooList? and how should I use it then?
Thomas
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