迭代器（Iterator）物件
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Python provides two general-purpose iterator objects.  The first, a
sequence iterator, works with an arbitrary sequence supporting the
"__getitem__()" method.  The second works with a callable object and a
sentinel value, calling the callable for each item in the sequence,
and ending the iteration when the sentinel value is returned.

PyTypeObject PySeqIter_Type

   Type object for iterator objects returned by "PySeqIter_New()" and
   the one-argument form of the "iter()" built-in function for built-
   in sequence types.

int PySeqIter_Check(op)

   Return true if the type of *op* is "PySeqIter_Type".

PyObject* PySeqIter_New(PyObject *seq)
    *Return value: New reference.*

   Return an iterator that works with a general sequence object,
   *seq*.  The iteration ends when the sequence raises "IndexError"
   for the subscripting operation.

PyTypeObject PyCallIter_Type

   Type object for iterator objects returned by "PyCallIter_New()" and
   the two-argument form of the "iter()" built-in function.

int PyCallIter_Check(op)

   Return true if the type of *op* is "PyCallIter_Type".

PyObject* PyCallIter_New(PyObject *callable, PyObject *sentinel)
    *Return value: New reference.*

   Return a new iterator.  The first parameter, *callable*, can be any
   Python callable object that can be called with no parameters; each
   call to it should return the next item in the iteration.  When
   *callable* returns a value equal to *sentinel*, the iteration will
   be terminated.
