[Python-ideas] Keyword same in right hand side of assignments (rev)

[Jacob Holm]

Steven D'Aprano wrote:
> On Wed, 18 Mar 2009 12:21:46 am Jacob Holm wrote:
>
>   
>> I believe that as soon as the left-hand side stops being a simple
>> variable and it is used in non-trivial expressions on the right-hand
>> side, using the keyword would help clarify the intent.  What I mean
>> is that the examples you should be looking at are more like:
>>
>> A[n+1] = same*same + 1
>> B[2*j].foo = frobnicate(same, same+1)
>> ...
>>
>> If you try expanding these into current python with minimal change in
>> semantics you will end up with something like
>>
>> _1 = n+1
>> _2 = A[_1]
>> A[_1] = _2*_2 + 1
>> del _1
>> del _2
>>
>> _1 = B[2*j]
>> _2 = _1.foo
>> _1.foo = frobnicate(_2, _2+1)
>> del _1
>> del _2
>>
>> which is much less readable.
>>     
>
> Of course it is, because it's obfuscated. What's with the leading 
> underscore names? Inside a function, they're not accessible to outside 
> callers, so the notion of "private" and "public" doesn't apply, and in 
> module-level code you delete them at the end, so they won't be imported 
> because they no longer exist. (BTW, there's no need to delete the names 
> one at a time. "del _1, _2" does what you want.)
>
> What's wrong with the clear, simple and obvious?
>
> A[n+1] = A[n+1]**2 + 1
>
>   
What is wrong is that it computes (n+1) twice, and it uses a different 
operator to avoid doing the __getitem__ twice. The whole point of the 
exercise was to get as close as possible to what I think the expression 
using "same" should mean. I tried to follow the common style for that 
kind of expansion as seen elsewhere on this list to make that clear. 
Obviously I failed.

Jacob