The “does Python have variables?” debate

[Ethan Furman]

On 05/08/2014 01:06 PM, Marko Rauhamaa wrote:
> Terry Reedy <tjreedy at udel.edu>:
>
>>> On Thu, May 8, 2014 at 6:07 PM, Joseph Martinot-Lagarde
>>> <joseph.martinot-lagarde at m4x.org> wrote:
>>>> For me, names bound to values is the same concept as pointer
>>>> pointing to memory.
>>
>> You are missing a level of indirection. In CPython, a name (always in
>> some namespace) represents a pointer to a pointer. The first pointer
>> is calculated as an offset from the base pointer of the namespace. For
>> a C array namespace (used for functions), the offset is constant (for
>> that function and namespace). For a python dict namespace, the offset
>> is calculated from the hash of the name, the size of the dict, and the
>> previous contents of the hash table. This complication allows the
>> namespace to grow and shrink. In either case, the second pointer if
>> overwritten to 'rebind' the name.
>
> Terry, you are talking about an implementation. Joseph is talking about
> the concept.
>
> You can tell a C programmer that a Python variable always holds a
> pointer to an object, and they get the idea right away ("Oh, so '.' in
> Python is the same as '->' in C") and start producing efficient, correct
> Python code.

Right up until they want to dereference.

--
~Ethan~