[Python-ideas] Adding "+" and "+=" operators to dict

[Ethan Furman]

On 02/14/2015 11:41 AM, Chris Barker wrote:
> On Sat, Feb 14, 2015 at 11:12 AM, Ethan Furman wrote:
>> On 02/13/2015 06:57 PM, Andrew Barnert wrote:

>> The current design of Python guarantees that an object always gets a setattr
>> or setitem when one of its elements is assigned to. That's an important property,
>> for the reasons I suggested above. So any change would have to preserve that
>> property. And skipping assignment when __iadd__ returns self would not preserve
>> that property. So it's not just backward-incompatible, it's bad.
> 
> --> some_var = ([1], 'abc')
> --> tmp = some_var[0]
> --> tmp += [2, 3]
> --> some_var
> ([1, 2, 3], 'abc')
> 
>     In that example, 'some_var' is modified without its __setitem__ ever being called.
> 
> not really -- an object in the some_var is modified -- there could be any number of other references to that object --
> so this is very much how python works.

Oops, I misread what Andrew was saying, sorry!

--
~Ethan~

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