[Python-ideas] One obvious way to do interning [Was: Retrieve an arbitrary element from a set without removing it]

[Georg Brandl]

Alexander Belopolsky schrieb:
> Changing the subject to reflect branched discussion and forwarding to
> python-ideas where it probably belongs.
> 
> On Mon, Oct 26, 2009 at 12:02 PM, Terry Reedy <tjreedy at udel.edu> wrote:
>> Alexander Belopolsky wrote:
>>
>>> Here is an alternative idea on how storing interned objects in a set
>>> can be supported.  Currently set.add method returns None and has no
>>> effect when set already has an object equal to the one being added.  I
>>> propose to consider changing that behavior to make set.add return the
>>> added object or the set member that is equal to the object being
>>> added.  It is unlikely that many programs rely on the return value
>>> being None (with doctests being a probable exception), so adding this
>>> feature is unlikely to cause much grief.
>>
>> I had exactly the same idea, but did not post because it violates the
>> general rule that mutators return None.
> 
> Is there such a rule?  What about set/dict pop?

The rule is about methods that do not have an obvious return value, where
the choice is between returning self and None.

Georg

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