Python C extension - Receiving a dict as argument

c, python, python-c-api, python-c-extension

Solution

You've got a couple problems here. First of all the `PyTypeObject` type is specifically for the struct that defines a type. You can read more about type objects here: http://docs.python.org/2/c-api/typeobj.html It's not what you want though. For a pointer to an arbitrary Python object you want to use `PyObject*`.

Second, the type code for an arbitrary Python object is `"O"` (uppercase) not `"o"`. If you want to do a type-check that it's a dictionary you can also use `"O!"` This requires you to pass the address of a type object followed by the address of the `PyObject*` you want to store the returned `PyObject*` into. For example:

PyObject* dict;
PyArg_ParseTuple(args, "O!", &PyDict_Type, &dict);

This will return the object into the *dict pointer, and raise a `TypeError` if it is not a dict. However unless you absolutely need it to be a dict I would recommend against this in favor of checking whether the object implements the mapping interface. But that's a different question.

Problem

I'm writing a C extension and I'm quite lost on how to receive a dict as an argument. As the docs don't have any specifics on how to achieve this I tried to parse the argument as a Python Object and then manipulate it as a dict: ``` PyTypeObject *dict; if(!PyArg_ParseTuple(args, "o", &dict)) return NULL; ``` But the code fails on the parsing: ``` Python 2.7.2 (default, Jun 20 2012, 16:23:33) [GCC 4.2.1 Compatible Apple Clang 4.0 (tags/Apple/clang-418.0.60)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import plotting >>> plotting.plot({'wff':0}) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: must be impossible<bad format char>, not dict ``` As far as I can understand from the error message the format char is wrong (I thought "o" should represent any Python object). What is the best way to parse a Python dict to a C pointer? I'm digging through the documentation but I haven't found anything similar to this. Thank you.

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