no side effects

["Martin v. Löwis"]

holger krekel wrote:
>     for i in [1,2,3]:
>         print i
>         i=3
> 
> the for-loop will iteratively bind the (local) name to  
> 1, then 2, then 3.  It never looks at the binding of
> the name 'i'.  With 'i=3' you only change the binding
> of 'i' to the object '3' but the for-loop will blindly
> change the binding again. 

This has nothing to do with namespaces: i is not local to the for loop, 
but might be global, or local to the function.

More relevant is that each for loop introduces a hidden variable. This 
hidden variable used to be an index into the sequence iterated over, and 
now is an iterator object which draws the next element from the sequence.

> To see the difference, in C, for example,  a name points 
> to a memory location and 'i=3;' will do something to 
> the memory location. 

The equivalent loop in C(++) would be

for(iterator_type iterator=sequence.begin();
     iterator != sequence.end(); iterator++){
   i = *iterator;
   print i;
   i = 3;
}

There is no way to access the hidden variable in Python.

Regards,
Martin