This patch allows any iterable to automatically support 
subscripting. 
 
Simple indices (itr[n]) will consume the iterator, and return 
the n'th item produced. 
 
Slice indices (itr[start:stop:step]) will produce an 
itertools.islice object created with the appropriate 
arguments. 
 
It also adds the C API function PyIter_GetItem which 
implements the above, and is invoked by 
PyObject_GetItem. 
 
Built and trivially tested on Suse Linux 9.1 from current 
CVS. 
 
Documentation and tests still to be added (Wednesday is 
a public holiday, so I will hopefully get to them then). 

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In for a penny, in for a pound. The new patch adds support for iterator 
concatenation (PyIter_Concat) and iterator repetition (PyIter_Repeat), 
based on itertools.chain and itertools.cycle respectively. 
 
The latter required adding an optional "times" argument to 
itertools.cycle. 
 
Augmented assignment is not supported in this patch. 
 
I also tweaked the behaviour of PyIter_GetItem, so its error handling 
was more like that of PySequence_GetItem. 
 
Finally, added a trivial test script that is barely deserving of the name, 
but does show that the thing basically works. 
 
Further work (i.e. proper tests. documentation, and cleaning up the 
code) will be dependent on BDFL approval. 

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Rejecting this myself, due partially to Guido's objections,
but also because I think this is better approached by
offering a base class which makes syntactic manipulation of
iterators more convenient (and possibly uses tee() internally).