On Tue, Jul 07, 2015 at 04:08:30PM +0200, Peter Otten wrote:
> For dicts and lists a method would work as well. Even now you can write
>
> items.pop(index) # instead of del items[index]
> lookup.pop(key) # del lookup[key]
>
> If you find the name pop() random or hard to discover a delete() method
> could be added.
>
> globals().pop("name") # instead of del name in the global namespace
> delattr(obj, "name") # del obj.name
>
> For the above the replacement is less elegant, but I don't think it matters
> for a rarely used feature. So for everything but local and nonlocal names
> del is syntactic sugar at best.
Not so. The point of del being a statement is that it should be
considered an operation on the *reference*, not the *value* of the
reference. So:
x = 23
delete(x) # if it existed, it would see the value 23
del x # operates on the reference "x", not 23
We can work around this by quoting the variable name:
delete("x") # this could work
but that is not an elegant design. It's a work-around for the fact that
Python doesn't have dedicated syntax to say "operate on the reference
foo" rather than the value of foo.
In Python, I think there are only two operations on references
themselves: binding, and unbinding. For some purposes, we can consider
unbinding just a special case of binding. (For example, adding a `del
spam` line to a function makes spam a local, just as assigning to it
would.) All binding operations are firstly statements, not function
calls:
x = 23 # not assign("x", 23)
import spam
for eggs in sequence
with expr as cheese
except SomeError as foo
and del is no exception. For some of these, there are functional
versions: setattr, delattr come to mind, but I don't think there are
many others. dict.pop and similiar are not conceptually the same, as
they don't operate on references, they operate on keys, indexes, names
as strings, etc.
I acknowledge that there is some overlap between the two, and one can
replace the other (at least sometimes), but conceptually they operate in
different spheres.
--
Steve
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