New submission from lesmana:
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
----------
components: Interpreter Core
messages: 188617
nosy: lesmana
priority: normal
severity: normal
status: open
title: explicit empty check instead of implicit booleaness
type: enhancement
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue17921>
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