Original idea by Guido van Rossum.
Idea for skipable inner iterators by Raymond Hettinger.
Idea for argument order and identity function default by Alex Martelli.
Implementation by Hye-Shik Chang (with tweaks by Raymond Hettinger).
Formerly, underlying queue was implemented in terms of two lists. The
new queue is a series of singly-linked fixed length lists.
The new implementation runs much faster, supports multi-way tees, and
allows tees of tees without additional memory costs.
The root ideas for this structure were contributed by Andrew Koenig
and Guido van Rossum.
* tee object is no longer subclassable
* independent iterators renamed to "itertools.tee_iterator"
* fixed doc string typo and added entry in the module doc string
* Add error checking code to PyList_Append() call.
* Replace PyObject_CallMethod(to->outbasket, "pop", NULL) with equivalent
in-line code. Inlining is important here because the search for the
pop method will occur for every element returned by the iterator.
* Make tee's dealloc() a little smarter. If the trailing iterator is
being deallocated, then the queue data is no longer needed and can
be freed.
It works like the pure python verion except:
* it stops storing data after of the iterators gets deallocated
* the data queue is implemented with two stacks instead of one dictionary.
