list.clear() missing?!?

[Steven D'Aprano]

On Tue, 11 Apr 2006 14:49:04 -0700, Ville Vainio wrote:

> John Salerno wrote:
> 
>> Thanks guys, your explanations are really helpful. I think what had me
>> confused at first was my understanding of what L[:] does on either side
>> of the assignment operator. On the left, it just chooses those elements
>> and edits them in place; on the right, it makes a copy of that list,
>> right? (Which I guess is still more or less *doing* the same thing, just
>> for different purposes)
> 
> Interestingly, if it was just a "clear" method nobody would be confused.

Even more importantly, you could say help(list.clear) and learn something
useful, instead of trying help(del) and getting a syntax error.
 
>>> help(del)
  File "<stdin>", line 1
    help(del)
           ^
SyntaxError: invalid syntax

I know Python isn't a purely OOP language, but in my opinion using
statements like del should be avoided when there is an easy and natural OO
way of doing it. Something like name.del() which means "delete the
reference to name in name's namespace" feels wrong, and may not even be
possible with Python's object model, so del name is a natural way to do
it. 

But name.clear() meaning "mutate the object referenced by name to the
empty state" is a very natural candidate for a method, and I don't
understand why lists shouldn't have it.

For lists, it would be natural to have a hypothetical clear() method
accept an index or slice as an argument, so that these are equivalent:

del L[:]  <=>  L.clear()
del L[n]  <=>  L.clear(n)
del L[a:b]  <=>  L.clear(slice(a, b))


# untested reference implementation:
class ClearableList(list):
    def clear(self, obj=None):
        if obj is None:
            obj = slice(0, len(self))
        if isinstance(obj, int):
            self.__delitem__(obj)
        elif isinstance(obj, slice):
            self.__delslice__(obj.start, obj.stop)
        else:
            raise TypeError


-- 
Steven.