Method Chaining

Rustom Mody rustompmody at gmail.com
Sun Jun 19 12:03:56 EDT 2016


On Sunday, June 19, 2016 at 9:26:54 PM UTC+5:30, Ethan Furman wrote:
> On 06/19/2016 08:14 AM, Michael Torrie wrote:
> > On 06/19/2016 09:01 AM, Ethan Furman wrote:
> >> On 06/19/2016 04:56 AM, Joonas Liik wrote:
> >>> On 18 June 2016 at 23:47, Ethan Furman wrote:
> >>>> On 06/18/2016 07:05 AM, Joonas Liik wrote:
> 
> >>>>> the leading dot does not resolve the ambiguity that arises from:
> >>>>>
> >>>>> with ob_a:
> >>>>>        with ob_b:
> >>>>>            .attr_c = 42 # which object are we modifying right now?
> >>>>
> >>>>
> >>>> The innermost one.  Why would it be anything else?
> >>>
> >>> What if ob_b does not have attribute attr_c but ob_a does?
> >>
> >> Good question.  I would say that _only_ the innermost with object is
> >> searched, and if it doesn't have the requested attribute an
> >> AttributeError is raised.  Otherwise, as you say, it could be a
> >> nightmare to maintain.
> >
> > But that wouldn't work either because it would make it impossible to
> > *set* attributes on an object.
> 
> Sure it would, just like any 'this_thing.whatever = 9' works just fine 
> if 'this_thing' doesn't already a `whatever` attribute.
> 
> The only thing that would change is being able to omit the 'this_thing' 
> portion; if you want to access an earlier 'with' obj, then you must be 
> explicit:
> 
>    with ob_a:
>       with ob_b:
>          ob_a.whatever = 9
>          .something_else = 10
> 
> > Python's dynamic nature just doesn't lend itself to this kind of ambiguity.
> 
> This is no more ambiguous than any other nested structure and, in some 
> cases, even simpler.

Yes to be clear the idea is mostly syntactic:
with ob_a :
 .some ...
 .other ... (maybe set or get ie lhs or rhs)

desugars to
ob_a.some ...
ob_a.other ...

And for an outer with the reach does not include and inner with
Just as in C if you have a nested switch the scope of the case-labels of the
outer excludes the inner


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