listerator clonage

[M.E.Farmer]

Cyril BAZIN wrote:
> Hello,
>
> I want to build a function which return values which appear two or
> more times in a list:
>
> So, I decided to write a little example which doesn't work:
> #l = [1, 7, 3, 4, 3, 2, 1]
> #i = iter(l)
> #for x in i:
> #    j = iter(i)
> #    for y in j:
> #        if x == y:
> #            print x

Py> i = [1,2,5,4,3,3,6,8,2,2,6]
Py> o = []
Py> for item in i:
...     if i.count(item) > 1 and item not in o:
...         o.append(item)
...
Py> print o
[2, 3, 6]

> In thinked that the instruction 'j= iter(i)' create a new iterator
'j'
> based on 'i' (some kind of clone). I wrote this little test which
show
> that 'j = iter(i)' is the same as 'j = i' (that makes me sad):
>
> #l = [1, 7, 3, 4, 2]
> #i = iter(l)
> #j = iter(i)
> #k = i
> #i, j, k
> (<listiterator object at 0x02167B50>, <listiterator object at
> 0x02167B50>, <listiterator object at 0x02167B50>)
Generally speaking Python sequence objects are iterable already no need
to cast them like java.
And yes iter() does create an iterator object.
Py> i = [1,2,5,4,3,3,6,8,2,2,6]
Py> e = iter(i)
Py> e
<stackless.iterator object at 0x010779E0>
Py> e.next()
1
Py> e.next()
2
Py> e.next()
5
Py> for item in e:
...     print item
...
4
3
3
6
8
2
2
6
But if you want a copy of a list then you can do it many other ways.
Py> i = [1,2,5,4,3,3,6,8,2,2,6]
Py> l = list(i)
Py>l
[1, 2, 5, 4, 3, 3, 6, 8, 2, 2, 6]
Py>i
[1, 2, 5, 4, 3, 3, 6, 8, 2, 2, 6]
Or,
Py> i = [1,2,5,4,3,3,6,8,2,2,6]
Py> l = i[:]
Py>l
[1, 2, 5, 4, 3, 3, 6, 8, 2, 2, 6]
Py>i
[1, 2, 5, 4, 3, 3, 6, 8, 2, 2, 6]
or you can even use copy,
Py> import copy
Py> i = [1,2,5,4,3,3,6,8,2,2,6]
Py> l = copy.copy(i)
Py> l
[1, 2, 5, 4, 3, 3, 6, 8, 2, 2, 6]

> Just in order to test, I wrote these little test:
> #l = [1, 7, 3, 4, 2]
> #i = iter(l)
> #import pickle
> #j = pickle.loads(pickle.dumps(i))
> Traceback (most recent call last):
>   File "<input>", line 1, in ?
>   File "C:\Python24\lib\pickle.py", line 1386, in dumps
>     Pickler(file, protocol, bin).dump(obj)
>   File "C:\Python24\lib\pickle.py", line 231, in dump
>     self.save(obj)
>   File "C:\Python24\lib\pickle.py", line 313, in save
>     rv = reduce(self.proto)
>   File "C:\Python24\lib\copy_reg.py", line 69, in _reduce_ex
>     raise TypeError, "can't pickle %s objects" % base.__name__
> TypeError: can't pickle listiterator objects
>
> #import copy
> #j = copy.copy(i)
> Traceback (most recent call last):
>   File "<input>", line 1, in ?
>   File "C:\Python24\lib\copy.py", line 95, in copy
>     return _reconstruct(x, rv, 0)
>   File "C:\Python24\lib\copy.py", line 320, in _reconstruct
>     y = callable(*args)
>   File "C:\Python24\lib\copy_reg.py", line 92, in __newobj__
>     return cls.__new__(cls, *args)
> TypeError: object.__new__(listiterator) is not safe, use
listiterator.__new__()
>
> So, I would like to know if there is a way to 'clone' a
'listiterator'
> object. I know that is possible in Java for example...
Just pickle the list not the iterator.

> If it is impossible, have you better ideas to find duplicate entries
> in a list...
See code example above.
> Thanks,
> 
> Cyril
Hth, 
M.E.Farmer