On Tue, Oct 17, 2017 at 3:18 AM, Stefan Ram <r...@zedat.fu-berlin.de> wrote:
> bartc <b...@freeuk.com> writes:
>>What about del team[2]?
>
> All arguments of a call are evaluated before the callable
> called then is incarnated with the values obtained. Assume,
> »team[ 2 ]« is bound to »8«. Then, the call
>
> f( team[ 2 ])«
>
> is equivalent to
>
> f( 8 )
>
> , and so »f« doesn't stand a chance of deleting »team[ 2 ]«.
>
> The evaluation rules for calls do not apply to the del-
> statement, however. Therefore,
>
> del team[ 2 ]
>
> is /not/ equivalent to
>
> del 8
>
> , and »del« can delete »team[ 2 ]« just fine. (Because the
> implementation can use whatever means available to it,
> since it is not bound to follow the evaluation rules for
> callables.)
Right, but you *could* implement a function that takes the two parts
and does the assignment or deletion:
def f(lst, idx):
del lst[idx]
f(team, 2)
The reason that 'del' absolutely has to be a statement is that it can
work on simple names, too:
del team
There's no way to do THAT part with a function call (it's basically
the opposite of assignment), so 'del' has to be a statement. Since
it's a statement, it may as well be able to do more than just simple
names, which means we have a consistent way to delete items from
arbitrary objects:
del globals()["foo"] # dicts
del sys.argv[1] # lists
etc
(Although you can't do this with sets. Sets are manipulated
exclusively through methods and operators.)
ChrisA
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