Objects in Python

[Chris Angelico]

On Thu, Aug 23, 2012 at 2:49 PM, Evan Driscoll <driscoll at cs.wisc.edu> wrote:
> On 8/22/2012 18:58, Ben Finney wrote:
>> You haven't discovered anything about types; what you have discovered is
>> that Python name bindings are not variables.
>>
>> In fact, Python doesn't have variables – not as C or Java programmers
>> would understand the term. What it has instead are references to objects
>> (with names as one kind of reference).
>
> OK, I've seen this said a few times, and I have to ask: what do you mean
> by this? I consider myself pretty decent at Python and other languages,
> and I really don't get it.

Simple example that'll work in many languages:

x = 1;

In C, this means: Assign the integer 1 to the variable x (possibly
with implicit type casting, eg to floating point).

In Java or C++, this means: Assign the integer 1 to the variable x.
Ditto, but possibly 'x' is actually a class member etc rather than a
simple variable.

In Python, this means: Make the name x now refer to the object 1.
Whatever x had before is de-referenced by one (in a simple refcounting
situation, that may result in the object being destroyed), and the
object referred to by the literal 1 is now pointed to by x.

Names are just one kind of reference because complex objects can have
unnamed references. For instance:

foo = [1, 2, 3]
foo[1] = "Hello, world!"

The second element of foo just got rebound in exactly the same way x
did, but it doesn't have a name of its own.

Does that sort things out, or just make things more confusing?

ChrisA