On 9/30/13 9:03 PM, Steven D'Aprano wrote:
On Mon, 30 Sep 2013 19:47:49 -0400, Ned Batchelder wrote:
On 9/30/13 6:37 PM, Ben Finney wrote:
Ethan Furman <et...@stoneleaf.us> writes:
From [Ned Batchelder]'s blog:
Names are Python's variables: they refer to values, and
those values can change (vary) over the course of your program.
This is partially incorrect. If the value referred to by the name is
immutable, then it cannot change; perhaps you meant to say that which
object the name points to can vary over time?
I agree. Names are not Python's variables.
If anything in Python is a “variable” as generally understood, it is
not a name. It is a *binding*, from a reference (a name, or some other
reference like a list item) to a value.
It is the binding which can change over the course of the program, so
that is the variable.
True, but no one calls the binding the variable. Here is a program:
x = 4
Every one of us is perfectly comfortable talking about the variable x.
Don't get hung up on implementation pedantry. The name x here refers to
4. Later it could refer to "four". The value associated with the name
x changed. x is a variable.
Your statement is ambiguous -- do you mean the *association* between
value (object) and name changed, or the value which is associated with
the name changed?
Yes, my statement was ambiguous. The value of x at time t1 can be
different than the value of x at time t2, and there are two different
ways it can differ. None of that changes the fact that the value
associated with the name varies over the course of a program, giving
rise to "variables."
I prefer to say that Python has variables, and they work by a mechanism
of names referring to values. I don't find that beginners get it by
being told that Python has no variables. It seems to be something that
experts sometimes find helpful, though.
--Ned.
In the first case, "the value associated with the name x changed" is no
different from saying "the name binding changed", only longer and more
ambiguous.
In the second case, if you mean that the association remains the same,
but the value itself changed, that's demonstrably untrue since 4 is
immutable. But you know that :-)
I straddle the fence on this dispute... I'll often refer to Python
variables when, in my option, it doesn't confuse the issue or introduce
ambiguity, but I feel guilty doing so :-) And I always look for the
opportunity to introduce the concept of name binding into the discussion.
I'm just not religious about it.
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