Arnaud Delobelle wrote:
> On Feb 17, 4:03 pm, Boris Borcic <[EMAIL PROTECTED]> wrote:
>> George Sakkis wrote:
>>> On Feb 17, 7:51 am, Arnaud Delobelle <[EMAIL PROTECTED]> wrote:
>>>> BTW, I keep using the idiom itertools.chain(*iterable). I guess that
>>>> during function calls *iterable gets expanded to a tuple. Wouldn't it
>>>> be nice to have an equivalent one-argument function that takes an
>>>> iterable of iterables and return the 'flattened' iterable?
>>> Indeed; I don't have any exact numbers but I roughly use this idiom as
>>> often or more as the case where chain() takes a known fixed number of
>>> arguments. The equivalent function you describe is trivial:
>>> def chain2(iter_of_iters):
>>> for iterable in iter_of_iters:
>>> for i in iterable:
>>> yield i
>> or fwiw
>>
>> chainstar = lambda iters : (x for it in iters for x in it)
>>
>> - a form that better suggests how to inline it in the calling expression, if
>> applicable.
>
> Indeed:
>
> def flattendict(d):
> def gen(d, pfx=()):
> return (x for k, v in d.iteritems()
> for x in (gen(v, pfx+(k,)) if isinstance(v, dict)
> else ((pfx+(k,), v),)))
> return dict(gen(d))
>
> I don't know, I find the chain(*...) version more readable,
In this case I could concede that it is, although I find both forms overly
convoluted for easy reading.
> although
> this one is probably better.
It is more elementary in the mathematician's sense, and therefore preferable all
other things being equal, imo. I've tried to split 'gen' but I can't say the
result is so much better.
def flattendict(d) :
gen = lambda L : (x for M in exp(L) for x in rec(M))
exp = lambda L : (L+list(kv) for kv in L.pop().iteritems())
rec = lambda M : gen(M) if isinstance(M[-1],dict) else [M]
return dict((tuple(L[:-1]),L[-1]) for L in gen([d]))
For fun I've also written a (vaguely prologish) non-recursive generator-based
version that exploits undocumented (but logical) behavior of list.extend
class iterstack(list) :
__iter__ = lambda self : self
def next(self) :
while self :
try :
return self[-1].next()
except StopIteration :
self.pop()
raise StopIteration
def flattendict(d,stk=[]) :
res={}
its=iterstack()
its.extend(stk[-1].iteritems()
for stk[len(its)-1:] in chain([[d]],its)
if isinstance(stk[-1],dict)
or res.update([(stk.pop(),tuple(stk))[::-1]]))
return res
(testing was minimal)
Challenge for who really has time to waste : replace the iterstack list
subclass
definition with a simple list + a generator expression inside flattendict.
Cheers, BB
--
http://mail.python.org/mailman/listinfo/python-list
