Hrvoje Niksic wrote:
> greg <[EMAIL PROTECTED]> writes:
>
> > none wrote:
> >> IIRC, I once saw an explanation how Python doesn't have
> >> "variables" in the sense that, say, C does, and instead has bindings
> >> from names to objects.
> >
IMHO, this is nonsense. All that variables are (in any language) are
"bindings" for names. Pretending python does anything novel with
regard to "variables" is confusing and, ultimately, simply results in
a redefinition of terms programmers are already familiar with. I
mean, it's kind of like saying my computer is not a computer but is
actually a device that follows input directions. Of course that
description may be true (and I may even use it to explain to students
*what* a computer is), but it is no less a computer for it.
> > If you're talking to C programmers, just tell them that Python
> > variables always contain pointers. That should give them the right
> > mental model to build on.
>
> That is a convenient shortcut when it works, but in my experience it
> tends to confuse the issue. The reason is that one of the main uses
> of pointers in C is implementing pass-by-reference. A C programmer
> told that Python variables internally hold pointers expects this code:
>
I think most C programmers are smart enough to figure out the supposed
differences, with only a little additional explanation on the part of
the instructor. Python's "variable model" is practically identical to
that of Java, after all, and I don't recall any discussion of
cataclysmic proportions over the differences between C "pointers" and
Java "references". There are "differences" (or more accurately
"points of emphasis"), but of the sort that take a paragraph or two of
explanation/clarification -- not a completely new model.
> def func(a):
> a = 10
> ...
> func(x)
>
> to change the value of x.
Depends on how you implement the C "equivalent". The most direct
translation, IMHO, is the following:
void func(int *a){
a = 10; //Of course this is nonsense, but it illustrates the
point. Just because "a" is a pointer
//does not mean that "a" is not rebound when it is
assigned to. Oh wait! Did I use
//the word "rebound" when talking about a *C*
variable? ;-)
//*a = 10; //I'm guessing this is what *you* had in mind, but it
is very different
}
int main(int argc, char **argv){
int x = 5;
func(&x);
printf("x is: %i\n", x);
return 0;
}
Which prints:
x is: 5
In this case, both the C and Python code have the same result.
--Nathan Davis
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