On 5/20/2014 12:30 PM, Chris Barker wrote:
>>>> [].sort() is None
> True
>>>> "ABC".lower() is None
> False
Is there a reference anywhere as to *why* the convention in Python is to
do it that way?
In short, reducing bugs induced by mutation of aliased objects.
Functional languages evade the problem by prohibiting mutation
(sometimes at the cost of inefficiency).
In an alternate universe, the example above might become
>>> a = []; a.sort() is a
True
>>> a = "ABC"' a.lower() is a
False
As I suggested earlier, having pure mutation methods not return anything
made is easy to suggest a mutation + non-self return method, list.pop.
If all mutation methods had previously returned 'self', there might have
been disagreement over whether the item return should augment or replace
the self return. Before you say the latter, consider the inconsistency
of only sometimes returning self and the potential consistency between
>>> most, last = 'a b c'.rsplit(maxsplit=1)
>>> most, last
('a b', 'c')
>>> most, last = [0, 1, 2].pop()
>>> most, last
([0, 1], 2)
One could also consider first, rest pairings.
--
Terry Jan Reedy
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