[Python-ideas] return value of yield expressions

[Ron Adam]

On Wed, 2011-09-14 at 17:30 +1000, Nick Coghlan wrote: 
> On Wed, Sep 14, 2011 at 3:01 PM, Ron Adam <ron3200 at gmail.com> wrote:
> > On Wed, 2011-09-14 at 13:41 +1000, Nick Coghlan wrote:
> >> On Wed, Sep 14, 2011 at 3:23 AM, Ron Adam <ron3200 at gmail.com> wrote:
> >> > If we could get the functions arguments when a function is done instead
> >> > of getting the return value.  (The modified function arguments object is
> >> > the return value in this case.)
> >> >
> >> >      fargs = &foo(a, b, c, d=4)
> >>
> >> This use case is covered by the bind() method in PEP 362 [1]:
> >>
> >>     foo_signature = inspect.signature(foo)
> >>     fargs = foo_signature.bind(a, b, c, d=4)
> >>
> >> [1] http://www.python.org/dev/peps/pep-0362/#signature-object
> >
> > It doesn't quite do the same thing, and it's not nearly as easy to use.
> 
> And magic syntax is better? 
> This is an incredibly niche use case, so
> there is zero justification for giving it special syntax when
> functions, methods and classes will do the job just fine (it's also
> worth keeping in mind that Guido hasn't even officially given PEP 362
> itself the nod at this point)

I don't know about it being a niche use case.   How many time is (*args,
**kwds) used to pass the signature data forward or back? 

I think this might be a lateral issue that could compliment Pep 362.


Thinking about it, I am able (with a bit of work) get the final
signature data mapping from within a function and return it.

def xupdate_map(map1, map2):
    """ Only update values in map1 from map2. """
    for k in map1.keys():
        map1[k] = map2[k]


def foo(v, count=2):
    sig_vals = locals() 

    # Do stuff that may change v and/or count.
    for n = range(count):
        v += 1

    return xupdate_map(sig_vals, locals())


That's pretty limiting and I can't call foo again with the result.  It's
also not very efficient either.


I need to play with this a bit more before I can really explain what I
seem to be thinking of.  If I get it pinned down with some real world
examples of how it would help, then maybe I'll post it here later.

The general idea is to be able to use the signature mapping "such as
what bind returns" in a more direct way with more freedom than *args,
and **kwds allows.


Cheers,
    Ron