When is del useful in Python?

I can't really think of any reason why Python needs the del keyword (and most languages seem to not have a similar keyword). For instance, rather than deleting a variable, one could just assign None to it. And when deleting from a dictionary, a del method could be added.

Is there a reason to keep del in Python, or is it a vestige of Python's pre-garbage collection days?

Solution 1:

Firstly, you can del other things besides local variables

del list_item[4]
del dictionary["alpha"]

Both of which should be clearly useful. Secondly, using del on a local variable makes the intent clearer. Compare:

del foo

to

foo = None

I know in the case of del foo that the intent is to remove the variable from scope. It's not clear that foo = None is doing that. If somebody just assigned foo = None I might think it was dead code. But I instantly know what somebody who codes del foo was trying to do.

Solution 2:

There's this part of what del does (from the Python Language Reference):

Deletion of a name removes the binding of that name from the local or global namespace

Assigning None to a name does not remove the binding of the name from the namespace.

(I suppose there could be some debate about whether removing a name binding is actually useful, but that's another question.)

Solution 3:

One place I've found del useful is cleaning up extraneous variables in for loops:

for x in some_list:
  do(x)
del x

Now you can be sure that x will be undefined if you use it outside the for loop.