How to convert a returned Python dictionary to a C++ std::map<string, string>

Question

I'm calling Python from C++, and trying to perform some data conversions.

For example, if I call the following Python function

def getAMap():
   data = {}
   data["AnItem 1"] = "Item value 1"
   data["AnItem 2"] = "Item value 2"
   return data

from C++ as:

PyObject *pValue= PyObject_CallObject(pFunc, NULL);

where pFunc is a PyObject* that points to the getAMap python function. Code for setting up pFunc omitted for clarity.

The returned pointer, pValue is a pointer to a (among other things) Python dictionary. Question is, how to get thh dictionary into a std::map on the C++ side as smoothly as possible?

I'm using C++ Builder bcc32 compiler that can't handle any fancy template code, like boost python, or C++11 syntax.

(Changed question as the python object is a dictionary, not a tuple)

Just found a library that makes it easy to convert Python objects (Python C API) to standard C++ datatypes as it says here. Looks like it might help you due to it also supports std::map. — Bee
– Bee, Commented Apr 23, 2018 at 20:09
David; that library looks great, but I can't use it with this compiler unfortunately. — Totte Karlsson
– Totte Karlsson, Commented Apr 23, 2018 at 20:44
i would use PyTuple_GetItem and copy the values into a map. Or write a swig typemap that does it for you. — Thomas
– Thomas, Commented Apr 23, 2018 at 20:49

Major · Accepted Answer · 2018-11-14 17:00:35Z

1

It's pretty ugly, but I came up with this:

std::map<std::string, std::string> my_map;

// Python Dictionary object
PyObject *pDict = PyObject_CallObject(pFunc, NULL);

// Both are Python List objects
PyObject *pKeys = PyDict_Keys(pDict);
PyObject *pValues = PyDict_Values(pDict);

for (Py_ssize_t i = 0; i < PyDict_Size(pDict); ++i) {
    // PyString_AsString returns a char*
    my_map.insert( std::pair<std::string, std::string>(
            *PyString_AsString( PyList_GetItem(pKeys,   i) ),
            *PyString_AsString( PyList_GetItem(pValues, i) ) );
}

edited Nov 14, 2018 at 17:00

answered Nov 13, 2018 at 22:14

Major

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