Whats is the way to clone "independen t" iterator? I can't use tee(),
because I don't know how many "independen t" iterators I need. copy and
deepcopy doesn't work...
--pavel 13 6365
Yosifov Pavel wrote:
Whats is the way to clone "independen t" iterator? I can't use tee(),
because I don't know how many "independen t" iterators I need. copy and
deepcopy doesn't work...
There is no general way. For "short" sequences you can store the items in a
list which is also the worst-case behaviour of tee().
What are you trying to do?
Peter
On 13 ÉÀÌ, 14:12, Peter Otten <__pete...@web. dewrote:
Yosifov Pavel wrote:
Whats is the way to clone "independen t" iterator? I can't use tee(),
because I don't know how many "independen t" iterators I need. copy and
deepcopy doesn't work...
There is no general way. For "short" sequences you can store the items ina
list which is also the worst-case behaviour of tee().
What are you trying to do?
Peter
I try to generate iterators (iterator of iterators). Peter, you are
right! Thank you. For example, it's possible to use something like
this:
def cloneiter( it ):
"""return (clonable,clone )"""
return tee(it)
and usage:
clonable,seq1 = cloneiter(seq)
...iter over seq1...
then clone again:
clonable,seq2 = cloneiter(clona ble)
...iter over seq2...
Or in class:
class ReIter:
def __init__( self, it ):
self._it = it
def __iter__( self ):
self._it,ret = tee(self._it)
return ret
and usage:
ri = ReIter(seq)
...iter over ri...
...again iter over ri...
...and again...
But I think (I'm sure!) it's deficiency of Python iterators! They are
not very good...
--Pavel
Yosifov Pavel wrote:
On 13 июл, 14:12, Peter Otten <__pete...@web. dewrote:
>Yosifov Pavel wrote:
Whats is the way to clone "independen t" iterator? I can't use tee(),
because I don't know how many "independen t" iterators I need. copy and
deepcopy doesn't work...
There is no general way. For "short" sequences you can store the items in a list which is also the worst-case behaviour of tee().
What are you trying to do?
Peter
I try to generate iterators (iterator of iterators). Peter, you are
right! Thank you. For example, it's possible to use something like
this:
def cloneiter( it ):
"""return (clonable,clone )"""
return tee(it)
[snip]
That is too abstract, sorry. What concrete problem are you trying to solve
with your cloned iterators? There might be a way to rearrange your setup in
a way that doesn't need them.
But I think (I'm sure!) it's deficiency of Python iterators! They are
not very good...
Well, I think Python's iterators, especially the generators, are beautiful.
More importantly, I think there is no general way to make iterators
copyable, regardless of the programming language. The problem is that most
of the useful ones depend on external state.
Peter
Well, I think Python's iterators, especially the generators, are beautiful.
More importantly, I think there is no general way to make iterators
copyable, regardless of the programming language. The problem is that most
of the useful ones depend on external state.
Peter
Hmm, but tee() de facto do it (clone iterator) and ignore side-effects
of iterator ("external" state). And tee() create independent
**internal** state of iterator (current position). But **external**
state - is headache of programmer. So, iterator/generator have to be
method for copy itself (the tee() implementation) or be "re-
startable". Why not?
Concrete problem was to generate iterators (iterator of slices). It
was solved with ReIter.
--Best regards,
--pavel
On Sun, 13 Jul 2008 18:51:19 -0700, Yosifov Pavel wrote:
>Well, I think Python's iterators, especially the generators, are beautiful. More importantly, I think there is no general way to make iterators copyable, regardless of the programming language. The problem is that most of the useful ones depend on external state.
Hmm, but tee() de facto do it (clone iterator) and ignore side-effects
of iterator ("external" state). And tee() create independent
**internal** state of iterator (current position).
`tee()` doesn't copy the iterator or its internal state but just caches
it's results, so you can iterate over them again. That makes only sense
if you expect to use the two iterators in a way they don't get much out of
sync. If your usage pattern is "consume iterator 1 fully, and then
re-iterate with iterator 2" `tee()` has no advantage over building a list
of all results of the original iterator and iterate over that twice.
`tee()` would be building this list anyway.
But **external** state - is headache of programmer. So,
iterator/generator have to be method for copy itself (the tee()
implementation) or be "re- startable". Why not?
Because it's often not possible without generating a list with all
results, and the advantage of a low memory footprint is lost.
Ciao,
Marc 'BlackJack' Rintsch
`tee()` doesn't copy the iterator or its internal state but just caches
it's results, so you can iterate over them again. That makes only sense
if you expect to use the two iterators in a way they don't get much out of
sync. If your usage pattern is "consume iterator 1 fully, and then
re-iterate with iterator 2" `tee()` has no advantage over building a list
of all results of the original iterator and iterate over that twice.
`tee()` would be building this list anyway.
It's interesting and a concrete answer. Thanks a lot.
Because it's often not possible without generating a list with all
results, and the advantage of a low memory footprint is lost.
Ciao,
Marc 'BlackJack' Rintsch
Seems like "monada". But I think is possible to determine when there
is a bounded external state (side-effects) or not, may be is needed
some new class-protocol for it... or something else. Or another way:
iterators may be re-iterable always, but if programmer need to point
to the extra- (external) state, he has to raise some a special
exception in __iter)) method... OK, it's only fantasies about language
design :-)
--pavel
On 13 juil, 12:05, Yosifov Pavel <b...@ngs.ruwro te:
(snip)
def cloneiter( it ):
"""return (clonable,clone )"""
return tee(it)
This might as well be written as
cloneiter = tee
Or yet better, just remove the above code and s/cloneiter/tee/g in the
remaining...
On 13 Jul., 08:53, Yosifov Pavel <b...@ngs.ruwro te:
Whats is the way to clone "independen t" iterator? I can't use tee(),
because I don't know how many "independen t" iterators I need. copy and
deepcopy doesn't work...
--pavel
You can try generator_tools http://pypi.python.org/pypi/generator_tools/0.3.3
On 14 ÉÀÌ, 23:36, "bruno.desthuil li...@gmail.com "
<bruno.desthuil li...@gmail.com wrote:
On 13 juil, 12:05, Yosifov Pavel <b...@ngs.ruwro te:
(snip)
defcloneiter( it ):
"""return (clonable,clone )"""
return tee(it)
This might as well be written as
cloneiter = tee
Or yet better, just remove the above code and s/cloneiter/tee/g in the
remaining...
Yes, sure. It was only for illustration. BUT: Marc Rintsch is right:
cloning of iterators in this manner is bad, more good is to use one,
single list(my_iter) instead of (see http://aquagnu.blogspot.com/2008/07/...n-python.html).
Thanks to all!
--pavel This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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