permuting over nested dicts?

[Boris Borcic]

Christian Meesters wrote:
> Hoi,
> 
> I have the following data structure (of variable size actually, to make
> things simple, just that one):
> d = {'a': {'x':[1,2,3], 'y':[4,5,6]},
>      'b': {'x':[7,8,9], 'y':[10,11,12]}}
> This can be read as a dict of possibilities: The entities 'a' and 'b' have
> the parameters 'x' and 'y', each. And d['a']['x'] can be either 1 or 2 or
> 3. Does anybody know a convenient (and fast) way to permute over all
> possible nested dicts like
> {'a': {'x':1, 'y':4},
>  'b': {'x':7, 'y':10}}
> and
> {'a': {'x':2, 'y':4},
>  'b': {'x':7, 'y':10}}
> and so forth?
> 
> Any link or snippet is appreciated.
> 
> TIA
> Christian

def cases(d) :
     import re
     bits = re.split('(\[.*?\])',repr(d))
     vv = [('_%s' % k, ' for _%s in %s' % (k,v))
             for k,v in enumerate(bits[1::2])]
     expr = [p+v for p,(v,_) in zip(bits[::2],vv)]+bits[-1:]+[v for _,v in vv]
     return eval('(%s)' % ''.join(expr))

for t in cases({'a': {'x':[1,2,3], 'y':[4,5,6]},
                    'b': {'x':[7,8,9], 'y':[10,11,12]}}) :
	print t

	
{'a': {'y': 4, 'x': 1}, 'b': {'y': 10, 'x': 7}}
{'a': {'y': 4, 'x': 1}, 'b': {'y': 10, 'x': 8}}
{'a': {'y': 4, 'x': 1}, 'b': {'y': 10, 'x': 9}}
{'a': {'y': 4, 'x': 1}, 'b': {'y': 11, 'x': 7}}
{'a': {'y': 4, 'x': 1}, 'b': {'y': 11, 'x': 8}}
{'a': {'y': 4, 'x': 1}, 'b': {'y': 11, 'x': 9}}
{'a': {'y': 4, 'x': 1}, 'b': {'y': 12, 'x': 7}}
{'a': {'y': 4, 'x': 1}, 'b': {'y': 12, 'x': 8}}
{'a': {'y': 4, 'x': 1}, 'b': {'y': 12, 'x': 9}}
{'a': {'y': 4, 'x': 2}, 'b': {'y': 10, 'x': 7}}
<snip/>

Caveats : (1) assert eval(repr(d))==d
           (2) no square bracket in either keys or values