[Python-ideas] Quick idea: defining variables from functions that take the variable name

[Sven R. Kunze]

On 01.06.2016 17:42, Paul Moore wrote:
> On 1 June 2016 at 16:10, Sven R. Kunze <srkunze at mail.de> wrote:
>> That's the current way. If now, the compiler would assign "x" to a special
>> dunder attribute/variable, that would allow __init__ to extract that name
>> and use it as if it were a parameter:
>>
>> class AutoSymbol:
>>      def __init__(self):
>>          self.name = __assigned_name__ # that's me :)
>>
> Why doesn't the assignment here set __assigned_name__ too, and
> override the value assigned by the "outer" assignment?

What's point with regards to the current discussion?

We need the name from the outer assignment. __assigned_name__ would 
solve that as it provides us with the needed piece of information. I 
don't see why an assignment on the same level where __assigned_name__ is 
used, should override this very __assigned_name__ variable. The 
assignment inside of __init__ might do so at a even deeper level but 
__assigned_name__ would stay constant *for* __init__ throughout the 
execution *of* __init__.

To me __assigned_name__ is just a magic variable as __module__ is. It is 
different from module to module. __assigned_name__ is different from 
function execution to function execution.


> Also, as someone else pointed out, in
>
> a = b = c = AutoSymbol()
>
> what would __assigned_name__ be?


That depends on which approach you choose. It's either dynamic and 
changes with each assignment or it is just set on the first assignment 
and never changes then.


I suspect most usecases need the latter. So, that speaks for the magic 
variable approach (independently of how characters are used for 
assignment operator and how we name that variable).


> The advantage of a special operation
> is that it gives you a way of pointing out precisely *which* name
> assignment we want to remember...

I don't know. I can't make a difference between = and ->. Just special 
characters. The one I know has a relatively clear meaning is =. So, I 
stick to it.


Best,
Sven
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