python dict clear只能删除一层，不能够递归删除。

 void
 PyDict_Clear(PyObject *op)
 {
     dictobject *mp;
     dictentry *ep, *table;
     int table_is_malloced;
     Py_ssize_t fill;
     dictentry small_copy[PyDict_MINSIZE];
 #ifdef Py_DEBUG
     Py_ssize_t i, n;
 #endif

     if (!PyDict_Check(op))
         return;
     mp = (dictobject *)op;
 #ifdef Py_DEBUG
     n = mp->ma_mask + ;
     i = ;
 #endif

     table = mp->ma_table;
     assert(table != NULL);
     table_is_malloced = table != mp->ma_smalltable;

     /* This is delicate.  During the process of clearing the dict,
      * decrefs can cause the dict to mutate.  To avoid fatal confusion
      * (voice of experience), we have to make the dict empty before
      * clearing the slots, and never refer to anything via mp->xxx while
      * clearing.
      */
     fill = mp->ma_fill;
     if (table_is_malloced)
         EMPTY_TO_MINSIZE(mp);

     else if (fill > ) {
         /* It's a small table with something that needs to be cleared.
          * Afraid the only safe way is to copy the dict entries into
          * another small table first.
          */
         memcpy(small_copy, table, sizeof(small_copy));
         table = small_copy;
         EMPTY_TO_MINSIZE(mp);
     }
     /* else it's a small table that's already empty */

     /* Now we can finally clear things.  If C had refcounts, we could
      * assert that the refcount on table is 1 now, i.e. that this function
      * has unique access to it, so decref side-effects can't alter it.
      */
     for (ep = table; fill > ; ++ep) {
 #ifdef Py_DEBUG
         assert(i < n);
         ++i;
 #endif
         if (ep->me_key) {
             --fill;
             Py_DECREF(ep->me_key);
             Py_XDECREF(ep->me_value);//只有这里处理了，但是如果value是一个字典，并且有其他地方引用了，那么就不能删掉了，我觉得应该递归删除
　　　　　　　/*i
　　　　　　　　　f(PyDict_Check(op->me_value))
　　　　　　　　　　{
　　　　　　　　　　　　PyDict_Clear(op->me_value);
　　　　　　　　　　}
　　　　　　　　else{

　　　　　　　　　　　　Py_XDECREF(ep->me_value);

　　　　　　　　　　}
　　　　　　　　*/
         }
 #ifdef Py_DEBUG
         else
             assert(ep->me_value == NULL);
 #endif
     }

     if (table_is_malloced)
         PyMem_DEL(table);
 }