[Tutor] Simple Question On A Method (in subclass)

[Steven D'Aprano]

Marc Tompkins wrote:
> It can be a little hard to wrap your head around how Python handles
> variables/objects; in other languages you create a variable and assign a
> value to it, while in Python you create an object and assign a name to it -
> the name can change while the object remains unchanged.  Here's a very
> simplified demo of what Dave is talking about:
[...]
> It's extremely logical, but almost entirely backward from the way most other
> languages do things.  Possibly it's because Guido is Dutch.

Fortunately, that is untrue.

I'm not sure where the myth that "Python is different from other 
languages" comes from. I suppose it is true only so far as *every* 
language is different from any other language (otherwise they would be 
the same language!). But Python is not so different from other common 
languages.

In particular, I don't know of any language where assignment means 
aliasing. Take the example Marc gave earlier:

t = 'this'
s = 'that'
group = [t, s]
print group  # => "['this', 'that']
s = 'the other'
print group  # => "['this', 'that']

I don't know of any language where the second item of group would now 
equal 'the other'. Pascal certainly isn't one:

program example (input, output);
var
   t,s: String(10);
   group: array[1..2] of String(10);
begin
   t:='this';
   s:='that';
   group[1]:=t;
   group[2]:=s;
   writeln(group[1], ' ', group[2]);
   s:='the other';
   writeln(group[1], ' ', group[2]);
end.


Running that program gives the equivalent output to Python:

this that
this that


PHP is the same. Using the PHP interactive shell:

php > $t = 'this';
php > $s = 'that';
php > $group[0] = $t;
php > $group[1] = $s;
php > print_r($group);
Array
(
     [0] => this
     [1] => that
)
php > $t = 'the other';
php > print_r($group);
Array
(
     [0] => this
     [1] => that
)


This myth of Python being radically different from other languages is 
especially mysterious since many of the most popular and common modern 
languages use *exactly* the same name binding execution model as Python, 
e.g. Java and Ruby. (In the case of Java, that only applies to boxed 
objects, and not unboxed low-level ints and similar. If this means 
nothing to you, feel fortunate.)




-- 
Steven