Am 13.07.2010 19:26, schrieb Roald de Vries:
> Hi all,
>
> I have two objects that should both be able to alter a shared float.
> So i need something like a mutable float object, or a float reference
> object. Does anybody know if something like that exists? I know it's
> not hard to build, but I have a feeling that there should be a
> standard solution to it.
Nice question to reflect our understanding of the basics of this language.
From what I know, we have the terms:
- reference
- name
(pointer is not really used beside from indices into lists or such)
I see it this way: you have named and unnamed references to objects.
This means you
can bind any number of names to an object as well as reference the
object in a list, tupe or set:
>>> (1,2,3) # unnamed references to int objects 1,2 and 3
>>> a=(1,2,3)[1] # binds a to tuple element #1 (int 2 object)
>>> b=a # now a and b are bound to the same int 2 object
So back to your question:
>>> a=b=1.0 # binds the names a and b to the same float object 1.0
>>> a,b
(1.0, 1.0)
now, there is no way to alter the float object since it is immutable (as
there are str, unicode, int, long, tuple...)
>>> a+=0.5
>>> a,b
(1.5, 1.0)
now you see even the "in place" addition creates a new object and
binds the name to it.
What you'd need to do would probably wrapping the float value into a
class where you can simulate a mutable float by providing a constant
name or reference for it within the class.
For example:
>>> a=b=[1.0]
>>> a[0]+=0.5
>>> a,b
([1.5], [1.5])
HTH
Tino
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