Python code to evaluate addition of two operands

ceval.c

case TARGET(BINARY_ADD): {
    PyObject *right = POP();
    PyObject *left = TOP();
    PyObject *sum;
    if (PyUnicode_CheckExact(left) &&
             PyUnicode_CheckExact(right)) {
        sum = unicode_concatenate(tstate, left, right, f, next_instr);
    }
    else {
        sum = PyNumber_Add(left, right);
    }
    SET_TOP(sum);
    ...
}