Recursive class | can you modify self directly?

Terry Reedy tjreedy at udel.edu
Wed Jul 10 21:33:25 CEST 2013


On 7/10/2013 4:58 AM, Russel Walker wrote:

> There is the name x and the class instance (the object) which exists
> somewhere in memory that x points to. self is just another name that
> points to the same object (not self in general but the argument
> passed to the self parameter when a method is called). However if the
> code inside the method reassigns self to some other object, it
> doesn't change the fact that x still refers to the original object.
> So self is just a local variable (an argument).

Yes, parameters *names* are the initial local names of the function. 
Calling the first parameter of instancemethods 'self' is a convention, 
not a requirement.

 > The name self has no
> relevance to to the name x other than the fact that they point to the
> same object. So reassigning self has no effect on x. But modifying
> the object that self points to, does affect x because it points to
> the same object. Is this correct?

Yes. Multiple names for one objects are 'aliases'. Being able to modify 
a object with multiple names in different namespaces is both a boon and 
bug bait.

> So when you call x.somemethod() it's not passing x as the self

Python does not pass'x': it is 'call-by-object', not 'call-by-name'.

> argument, it's actually passing the object that x points to as the
> self argument. And that object has know knowledge of the fact that x
> points to it, or does it?

Some objects (modules, classes, functions) have definition names 
(.__name__ attributes) that are used in their representations (as in 
tracebacks). But they have no knowledge of their namespace names.



-- 
Terry Jan Reedy




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