疊代器（Iterator）物件
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Python 提供了兩種通用的疊代器 (iterator) 物件，第一種是序列疊代器
(sequence iterator)，適用於支援 "__getitem__()" 方法的任意序列，第二種
是與可呼叫 (callable) 物件和哨兵值 (sentinel value) 一起使用，會呼叫序
列中的每個可呼叫物件，當回傳哨兵值時就結束疊代。

PyTypeObject PySeqIter_Type
    * 為 穩定 ABI 的一部分.*

   此型別物件用於由 "PySeqIter_New()" 所回傳的疊代器物件以及用於內建序
   列型別的內建函式 "iter()" 的單引數形式。

int PySeqIter_Check(PyObject *op)

   Return true if the type of *op* is "PySeqIter_Type".  This function
   always succeeds.

PyObject *PySeqIter_New(PyObject *seq)
    *回傳值：新的參照。** 為 穩定 ABI 的一部分.*

   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
    * 為 穩定 ABI 的一部分.*

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

int PyCallIter_Check(PyObject *op)

   Return true if the type of *op* is "PyCallIter_Type".  This
   function always succeeds.

PyObject *PyCallIter_New(PyObject *callable, PyObject *sentinel)
    *回傳值：新的參照。** 為 穩定 ABI 的一部分.*

   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.
