When is del useful in python?

Question

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 deletin

Answer 1

As an example of what del can be used for, I find it useful i situations like this:

def f(a, b, c=3):
    return '{} {} {}'.format(a, b, c)

def g(**kwargs):
    if 'c' in kwargs and kwargs['c'] is None:
        del kwargs['c']

    return f(**kwargs)

# g(a=1, b=2, c=None) === '1 2 3'
# g(a=1, b=2) === '1 2 3'
# g(a=1, b=2, c=4) === '1 2 4'

These two functions can be in different packages/modules and the programmer doesn't need to know what default value argument c in f actually have. So by using kwargs in combination with del you can say "I want the default value on c" by setting it to None (or in this case also leave it).

You could do the same thing with something like:

def g(a, b, c=None):
    kwargs = {'a': a,
              'b': b}
    if c is not None:
        kwargs['c'] = c

    return f(**kwargs)

However I find the previous example more DRY and elegant.

Answer 2

del is the equivalent of "unset" in many languages and as a cross reference point moving from another language to python.. people tend to look for commands that do the same thing that they used to do in their first language... also setting a var to "" or none doesn't really remove the var from scope..it just empties its value the name of the var itself would still be stored in memory...why?!? in a memory intensive script..keeping trash behind its just a no no and anyways...every language out there has some form of an "unset/delete" var function..why not python?

Answer 3

Every object in python has an identifier, Type, reference count associated with it, when we use del the reference count is reduced, when the reference count becomes zero it is a potential candidate for getting garbage collected. This differentiates the del when compared to setting an identifier to None. In later case it simply means the object is just left out wild( until we are out of scope in which case the count is reduced) and simply now the identifier point to some other object(memory location).