On 4/21/2012 9:08 AM, Dave Angel wrote:
On 04/21/2012 08:48 AM, Bernd Nawothnig wrote:
On 2012-04-20, Rotwang wrote:
since a method doesn't assign the value it returns to the instance on
which it is called; what it does to the instance and what it returns are
two completely different things.
Returning a None-value is pretty useless. Why not returning self, which would be
the resulting list in this case? Returning self would make the
language a little bit more functional, without any drawback.
Then nested calls like
a = [].append('x').append('y').append('z')
Sequential appends are nearly always done within a loop.
would be possible with a containing the resulting list
['x', 'y', 'z'].
This has been debated here many times. The python reasoning for most
cases goes something like this:
A function/method on an object may either alter the object, or produce a
new one and return that. If it does both, the programmer can get
surprised and have a bug that's difficult to notice.
For example, you can either sort() a list, in which case it's done
in-place, returning none. Or you can call sorted() on it, which
returns a new list, similar to the first, but sorted.
Guido having decided to consistently not return mutated objects,
perhaps partly on the basis that the caller could already have a
reference to the object, it was easy a decade or more later to add
various methods/functions, including pop() and next(), that mutate by
removing and returning an object, while remaining consistent with the rule.
--
Terry Jan Reedy
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