Steve D'Aprano <steve+pyt...@pearwood.info> writes:
> On Tue, 17 Oct 2017 03:16 am, Oren Ben-Kiki wrote:
>
> > That doesn't explain why `del` isn't a method though.
>
> `del` cannot be a method or a function, because the argument to `del`
> is the name of the variable, not the contents of the variable.
Since a Python “variable” does not have contents, this is IMO another
instance where using the term “variable” is not helpful.
>>> x = 123
>>> y = [0, x, 2, x, 4]
Neither of the names ‘x’ nor ‘y’ have content; they are references to
objects. The list itself also has references, which the Python code can
use to get at the items.
>>> y
[0, 123, 2, 123, 4]
>>> y[1]
123
So when we give an argument to ‘del’, that argument is not always a
“variable”; it is always a reference.
We can delete one item from a list, because that item is accessed via a
reference; we give the same reference as argument to ‘del’::
>>> del y[1]
Both ‘x’ and ‘y’ remain bound. The reference that was at index 1 of the
above list is deleted.
>>> x
123
>>> y
[0, 2, 123, 4]
> then `del` needs to delete the *name* "x", not the value of x, namely
> 123. If del were a function or method, it would only see the value,
> 123, and have no idea what the name is.
Hopefully when one thinks in terms of references – and the use of a
non-name reference, above, may make that distinction clear – the
operation of ‘del’ is easier to understand.
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Ben Finney
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