Conversion from tuple to argument list?

[mmillikan at vfa.com]

mmillikan at vfa.com writes:
<snip>

> However, it doesn't work when the sequence to be unpacked is in any other
> position in the parameter list:
> 
> >>> zip(*seqseq,seq)
>   File "<stdin>", line 1
>     zip(*seqseq,seq)
>                   ^
> SyntaxError: invalid syntax
> 
> Could this syntax be extended to allow the splicing to happen at any
> position within the parameter list?
> 
> In the interim, the following module allows the construction:
> 
> >>> zip(*splice(unnest(seqseq),seq))
> [(1, 'a', 'x'), (2, 'b', 'y'), (3, 'c', 'z')]
> 
> More elaborate splicing also appears to work:
> 
> >>> splice([10,20,30],[],unnest(['sam',unnest(unnest(['barney','fred']))]),seq,())
> [[10, 20, 30], [], 'sam', 'barney', 'fred', ('x', 'y', 'z'), ()]
> 
> Only lightly tested, on 2.1.1
> 
> Feedback on utility and/or horrible flaws appreciated
> 
> ------------------------------------------------------------------

simplified to ...

#splice3.py
from __future__ import nested_scopes

class unnest:
    '''A minimal wrapper for any sequence. When passed
    as an argument to the <splice> function the elements
    of the sequence will be spliced into the list returned
    replacing the <unnest> instance.'''
    
    def __init__(self,seq):
        if isinstance(seq,self.__class__):
            self.seq = seq.seq
        else: 
            for item in seq: break
            self.seq = seq
            
    def __getitem__(self,index):
        return self.seq[index]
        
    def __len__(self):
        return len(self.seq)

def splice(*args):
    '''Returns a list of its args with any instances
    of <unnest> replaced by the items of the unnests
    sequence attribute.'''
    
    def _splice(flat,*args): 
        for arg in args:
            if isinstance(arg,unnest):
                _splice(flat,*arg.seq)
            else:
                flat.append(arg)
        return flat
            
    return _splice([],*args)