CPython - Read Python Dictionary (keys/values) inside a C Function Passed as argument

Question

I am writing a Python C extension. I am passing a Python dict to a C function. I am able to parse it, using the following code:

PyObject *large_dict = NULL;
if (!PyArg_ParseTuple(args, "O!", &PyDict_Type, &large_dict)) return NULL;
if (large_dict != NULL)
{
   printf("Large Dictionary Not Null\n");
}

Here the statement "Large Dictionary Not Null" is printed, which means that the dictionary is parsed successfully. Now I want to access the dictionary values by specifying keys, like we do in Python. For example, large_dict['k1'] would give value v1.

How can I access dictionary keys/values inside this C function?

Answer 1

You should go through the link, https://docs.python.org/2/c-api/dict.html Excerpt given below,

PyObject* PyDict_GetItem(PyObject *p, PyObject *key)
Return value: Borrowed reference.
Return the object from dictionary p which has a key key. Return NULL if the key key is not present, but without setting an exception.

PyObject* PyDict_GetItemString(PyObject *p, const char *key)
Return value: Borrowed reference.
This is the same as PyDict_GetItem(), but key is specified as a char*, rather than a PyObject*.

PyObject* PyDict_Items(PyObject *p)
Return value: New reference.
Return a PyListObject containing all the items from the dictionary, as in the dictionary method dict.items().

PyObject* PyDict_Keys(PyObject *p)
Return value: New reference.
Return a PyListObject containing all the keys from the dictionary, as in the dictionary method dict.keys().

PyObject* PyDict_Values(PyObject *p)
Return value: New reference.
Return a PyListObject containing all the values from the dictionary p, as in the dictionary method dict.values().

Keep an eye on borrowed reference / new reference. It is little tricky while coding for Python extensions.