On 12/06/13 19:32, Khalid Al-Ghamdi wrote:
Hi,
Why doesn't this work? And is there way to have an
object immediately return a value or object once it is instantiated with
using a method call?
It does return a value. It returns the object that was just instantiated.
Supposed you could do what you wanted:
1. >>> class k:
2. def __init__(self,n):
3. return n*n
4.
5.
6. >>> khalid=k(3)
and khalid receives the value 9. That would be useless, because the instance of
class K would be immediately destroyed.
If you want to just return a value, use a function. This is the best solution:
def k(n):
return n*n
khalid = k(3)
assert khalid == 9
Another alternative is to create a callable object:
class K:
def __init__(self, n):
self.n = n
def __call__(self, arg):
return arg * self.n
k = K(3)
k(2)
=> returns 6
k(5)
=> returns 15
A third alternative is to use the __new__ method. This only works in Python 3,
or for new-style classes that inherit from object:
class K(object):
def __new__(cls, n):
return n*n
but don't do this. Really, don't. There are advanced uses where this is useful,
but for this trivial example, you should just use a function.
--
Steven
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