shy stackless Re: ANNOUNCE: xsdb -- the eXtremely Simple Database goes alpha

Duncan Booth duncan at NOSPAMrcp.co.uk
Thu Dec 11 16:50:07 CET 2003


Jp Calderone <exarkun at intarweb.us> wrote in
news:mailman.68.1071152873.9307.python-list at python.org: 

>   This works, but it is even easier.  All you need is top-level code
>   to 
> handle it:
> 
> 
>     def unroll(f, *a, **kw):
>         gstack = [iter(f(*a, **kw))]
>         while gstack:
>             try:
>                 e = gstack[-1].next()
>             except StopIteration:
>                 gstack.pop()
>             else:
>                 if isinstance(e, types.GeneratorType):
>                     gstack.append(e)
>                 else:
>                     yield e
> 
> 
>     def inorder(t):
>         if t:
>             yield inorder(t.left)
>             yield t.label
>             yield inorder(t.right)
> 
>     unroll(inorder, t)
> 
> 
>     A bit more frameworky code, but it's all isolated in one place,
>     which is 
> much nicer than having to spread it all over the place.

Nice idea, provided you never want to yield a generator. Also should it 
check for a generator, or just for any iterator.

You can also go for a recursive definition of unroll and use it to unroll 
itself which I think reads a bit more clearly.

def unroll(iterator):
    for v in iterator:
        if isinstance(v, types.GeneratorType)
            for inner in unroll(v): yield inner
        else:
            yield v

for node in unroll(inorder(t)):
   ... do whatever ...

I wonder if this is useful enough to go in itertools?

-- 
Duncan Booth                                             duncan at rcp.co.uk
int month(char *p){return(124864/((p[0]+p[1]-p[2]&0x1f)+1)%12)["\5\x8\3"
"\6\7\xb\1\x9\xa\2\0\4"];} // Who said my code was obscure?




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