overriding equals operation

[Thomas Rachel]

Am 16.10.2012 15:51 schrieb Pradipto Banerjee:

> I am trying to define class, where if I use a statement a = b, then instead of "a" pointing to the same instance as "b", it should point to a copy of "b", but I can't get it right.

This is not possible.


> Currently, I have the following:
>
> ----
>
> class myclass(object):

Myclass or MyClass, see http://www.python.org/dev/peps/pep-0008/.

>          def __eq__(self, other):
>                  if instance(other, myclass):
>                          return self == other.copy()
>                  return NotImplemented

This redefines the == operator, not the = operator.

It is not possible to redefine =.

One way could be to override assignment of a class attribute. But this 
won't be enough, I think.

Let me explain:

class MyContainer(object):
     @property
     def content(self):
         return self._content
     @content.setter
     def content(self, new):
         self._content = new.copy()

Then you can do:

a = MyClass()
b = MyContainer()
b.content = a
print b.content is a # should print False; untested...

But something like

a = MyClass()
b = a

will always lead to "b is a".

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What?


Thomas