Closures in leu of pointers?

[Steven D'Aprano]

On Sat, 29 Jun 2013 12:35:54 -0600, Michael Torrie wrote:

> Python's
> basic data types are immutable.  At best we could say they are read-only
> variables.

Python's basic data types are not necessarily immutable. Lists and dicts 
are not immutable. Being a high-level language, the idea of "primitives" 
like int, double, float, etc from C doesn't really apply. A Python dict 
is not made up from Python ints. Both int and dict are equally "basic".

More importantly, you are conflating the idea of a variable (a name) and 
the value of that variable (a value). Whether a variable is a named 
memory location or a name binding in a namespace, it's still a name. Ints 
are not names, whether they are low-level C ints or Python int objects. 
Comparing the immutability of an int object (value) with the ability to 
write to a name ("read-only variable" == constant) confuses the value and 
the name, which is exactly what we're trying to get away from.


> So no, saying Python doesn't have variables is not the same as saying C
> doesn't have variables but only memory locations.  They are different
> concepts entirely, though on the surface they look similar.

Antoon is suggesting that instead of defining:

"A variable is a named memory location, like in C"

and therefore concluding that Python doesn't have variables, we could 
define:

"A variable is a name in a namespace bound to a value, like in Lisp"

and therefore conclude that Python does have variables, but C doesn't.

It's not that the two definitions are "different concepts entirely", but 
that they are two subtly different forms of the same concept, a mapping 
between names and values.

If they were entirely different concepts, like a list and an int, you 
wouldn't have people confusing them. Nobody ever asks why Python doesn't 
let you sort an int, or take the square of a list...


-- 
Steven