python dict clear只能删除一层，不能够递归删除。

 1 void
 2 PyDict_Clear(PyObject *op)
 3 {
 4     dictobject *mp;
 5     dictentry *ep, *table;
 6     int table_is_malloced;
 7     Py_ssize_t fill;
 8     dictentry small_copy[PyDict_MINSIZE];
 9 #ifdef Py_DEBUG
10     Py_ssize_t i, n;
11 #endif
12
13     if (!PyDict_Check(op))
14         return;
15     mp = (dictobject *)op;
16 #ifdef Py_DEBUG
17     n = mp->ma_mask + 1;
18     i = 0;
19 #endif
20
21     table = mp->ma_table;
22     assert(table != NULL);
23     table_is_malloced = table != mp->ma_smalltable;
24
25     /* This is delicate.  During the process of clearing the dict,
26      * decrefs can cause the dict to mutate.  To avoid fatal confusion
27      * (voice of experience), we have to make the dict empty before
28      * clearing the slots, and never refer to anything via mp->xxx while
29      * clearing.
30      */
31     fill = mp->ma_fill;
32     if (table_is_malloced)
33         EMPTY_TO_MINSIZE(mp);
34
35     else if (fill > 0) {
36         /* It‘s a small table with something that needs to be cleared.
37          * Afraid the only safe way is to copy the dict entries into
38          * another small table first.
39          */
40         memcpy(small_copy, table, sizeof(small_copy));
41         table = small_copy;
42         EMPTY_TO_MINSIZE(mp);
43     }
44     /* else it‘s a small table that‘s already empty */
45
46     /* Now we can finally clear things.  If C had refcounts, we could
47      * assert that the refcount on table is 1 now, i.e. that this function
48      * has unique access to it, so decref side-effects can‘t alter it.
49      */
50     for (ep = table; fill > 0; ++ep) {
51 #ifdef Py_DEBUG
52         assert(i < n);
53         ++i;
54 #endif
55         if (ep->me_key) {
56             --fill;
57             Py_DECREF(ep->me_key);
58             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);

　　　　　　　　　　}　　　　　　　　*/
59         }
60 #ifdef Py_DEBUG
61         else
62             assert(ep->me_value == NULL);
63 #endif
64     }
65
66     if (table_is_malloced)
67         PyMem_DEL(table);
68 }