[Tutor] working with strings in python3

[Alan Gauld]

"Rance Hall" <ranceh at gmail.com> wrote

> Variables are variable, that's why we call them variable.

Yes, but Programming variables(*) are variable in the sense 
that they can represent different values over time. That is 
not the same as requiring the values themselves to change.

> The idea of immutable strings variables blurs the 
> line between these two mathematical concepts 

Not at all. In math you can have a variable reference 
the number 42. Later the same variable may represent 
a different number, 66 say. But 66 and 42 are different, 
immutable numbers. It is no different with strings in Python.
A variable can refer to 'foo'; at one point and 'bar' at another. 
But 'foo' and 'bar' (and indeed 'foobar') are different values 
just as 42, 66 and 108 are different numbers. Python 
strings act like numbers in that regard.

> variable is variable or mutable, where a keyname can not be.

variables are always variable but only some values 
are mutable You are conflating variables and values. 
Strings are values (or objects if you prefer) and (arbitrarily) 
chosen to be immutable by Guido. Variables are associated 
with values and the values with which they are associated 
can, and do, change.

(*)Note that variables in programming are treated differently 
from traditional math variables in that math variables are usually 
considered as symbols for a constant, unchanging value. 
It is unusual in math to say

Let x = 42
.... stuff ....
Let x = 66

We would introduce a new variable for the new value.
But that idiom is very common in programming generally.


HTH,

-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/