Re: variable length tuple assignment
Tim Chase wrote: > As an aside, as of the last time I read the PEP[1] on this, I > believe it exhausts (or attempts to exhaust) any iterator. IMHO, > I think this exhausting is a bad idea because it prevents things like > >def numbers(start=0): > i = start > while True: >yield i >i += 1 > >CONST_A, CONST_B, CONST_C, *rest = numbers() > > which will hang in current Py3.0 until you blow a stack or > overrun your heap somewhere because it will try to exhaust the > infinite loop. But what else can it do? Do you expect Python to read your mind and magically know when you intend to use rest and when you're intending to just throw it away? Perhaps Python could do that, via static analysis -- if rest is never used again, don't bother exhausting the iterator. But that will lead to differences in iterators that have side-effects. It will also have a subtle difference in behaviour here: it = xrange(5) # for example a, b, c, *rest = it L = list(it) # L is now [3, 4] versus a, b, c, *rest = xrange(5) parrot(rest) L = list(it) # L is now [] > It also changes the type from iter() to list() > for the remaining content (not as grevious). But that's what unpacking does. It would be a major semantic change for x, *s = some_iterator to make s an alias of some_iterator. And why would you want it to? If you do, just do this: x, s = some_iterator.next(), some_iterator -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: variable length tuple assignment
Chris Rebert wrote:
On Wed, Feb 25, 2009 at 1:16 AM, Helmut Jarausch
wrote:
Sorry if this is too simple but I couldn't find.
I vaguely remember there is a means to assign a variable length tuple
and catch the 'rest' like
S="a,b,c,d"
(A,B,) = S.split(',')
In Python 3.0 (IIRC):
A, B, *rest = S.split(',')
As an aside, as of the last time I read the PEP[1] on this, I
believe it exhausts (or attempts to exhaust) any iterator. IMHO,
I think this exhausting is a bad idea because it prevents things like
def numbers(start=0):
i = start
while True:
yield i
i += 1
CONST_A, CONST_B, CONST_C, *rest = numbers()
which will hang in current Py3.0 until you blow a stack or
overrun your heap somewhere because it will try to exhaust the
infinite loop. It also changes the type from iter() to list()
for the remaining content (not as grevious).
I agree that the "internal star" usage needs to exhaust the iterator:
A, *rest, C, D = s.split(',')
but the terminal-star syntax should be a little more gracious
with iterators.
Anyways, my $0.02 (minus taxes, money for multiple bailouts, and
deflated by economic conditions -- so not worth much :).
-tkc
[1]
http://www.python.org/dev/peps/pep-3132/
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Re: variable length tuple assignment
On Wed, Feb 25, 2009 at 1:16 AM, Helmut Jarausch
wrote:
> Sorry if this is too simple but I couldn't find.
>
> I vaguely remember there is a means to assign a variable length tuple
> and catch the 'rest' like
>
> S="a,b,c,d"
>
> (A,B,) = S.split(',')
In Python 3.0 (IIRC):
A, B, *rest = S.split(',')
Cheers,
Chris
--
Follow the path of the Iguana...
http://rebertia.com
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variable length tuple assignment
Sorry if this is too simple but I couldn't find.
I vaguely remember there is a means to assign a variable length tuple
and catch the 'rest' like
S="a,b,c,d"
(A,B,) = S.split(',')
I know I could do
SL= split(',')
(A,B)=SL[:2]
Rest= SL[2:]
but is there some shorthand for this?
Many thanks for a hint,
Helmut Jarausch
Lehrstuhl fuer Numerische Mathematik
RWTH - Aachen University
D 52056 Aachen, Germany
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