Issue 17921: explicit empty check instead of implicit booleaness (original) (raw)

Issue17921

Created on 2013-05-07 02:18 by lesmana, last changed 2022-04-11 14:57 by admin. This issue is now closed.

Messages (3)
msg188617 - (view)	Author: lesmana (lesmana)	Date: 2013-05-07 02:18
Python should have a builtin method `isempty()` which calls the special method name `__isempty__()` for explicit emptiness check. The special method `__isempty__()` should return `True` if the object is "empty" and `False` if the object is "not empty". Observe emptiness check using implicit booleaness: if not somecollection: foo() Note that this code also handles `None`, `0` and `False` silently. If those are possible values then I have to test explicitly: if somecollection is not None and not somecollection: foo() Also handling the `0` and `False` cases will make the code really really ugly. Usually the `None`, `0` or `False` cases only happen in case of a programming error. But if I do not test for them explicitly then they will be handled silently and the error will occur somewhere else in the code. Compare against explicit emptiness check: if not isempty(somecollection): foo() This code will break immediately if somecollection does not have `__isempty__()`. If `None`, `0` or `False` are possible values they will not be handled silently, instead an error will be reported at `isempty()`. Advantage of explicit emptiness check: * More explicit and fluently readable code * No silent implicit booleaness check when code should do emptiness check * Clearer separation of meaning for the special methods `__len__()` and `__empty__()` Possible use case for explicit emptiness check: a list with memory effect. >>> ml = MemoryEffectList() >>> ml.charge() >>> ml.discharge() >>> isempty(ml) True >>> len(ml) == 0 False
msg188618 - (view)	Author: R. David Murray (r.david.murray) *	Date: 2013-05-07 02:23
Just use len.
msg188619 - (view)	Author: R. David Murray (r.david.murray) *	Date: 2013-05-07 02:26
Or, to be more helpful than that short answer: if you think there is something that isempty can do that len can't that makes it worth adding complexity to the language, please discuss it on the python-ideas mailing list first. That's the best place to get feedback for ideas like this.