爲什麼Python不會捕獲在C++中引發的異常？

Question

我想在boost :: python中做一個Python迭代器。所以我有一個功能

PyObject *my_iterator_next(MyIterator *iter) { 
    if (!iter->is_end()) { 
     return *(*iter)++; 
    } 
    else { 
     PyErr_SetNone(PyExc_StopIteration); 
     // this doesn't work either 
     // PyErr_SetString(PyExc_StopIteration, "end of collection"); 
     return NULL; 
    } 
} 

在Python：

// x is MyContainer([1, 2, 3]) 
for x in my_container: 
    print(x) 

我也得到：

1 
2 
3 
NoneTraceback (most recent call last): 
    File "main.py", line 6, in <module> 
    print(x) 
StopIteration: end of collection 

而且

it = my_collection.__iter__() 
try: 
    it.__next__(); 
    it.__next__(); 
    it.__next__(); 
    it.__next__(); 
except: 
    print("caught exception") 

這個代碼不打印任何東西，所以沒有發現任何類型的異常。

爲什麼？

Answer 1

設置Python異常後，必須像這樣通知的Boost.Python：

throw_error_already_set(); 

見http://www.boost.org/doc/libs/1_35_0/libs/python/doc/v2/errors.html