The PVM – Python Virtual Machine

If you want to follow along in the Python source code, the relevant file is https://github.com/python/cpython/blob/master/Python/ceval.c. The interpreter is a loop over a big switch statement on the byte codes. Most operations are pretty simple. For example, here is the implementation of the BINARY_MULTIPLY instruction:

        case TARGET(BINARY_MULTIPLY): {
            PyObject *right = POP();
            PyObject *left = TOP();
            PyObject *res = PyNumber_Multiply(left, right);
            Py_DECREF(left);
            Py_DECREF(right);
            SET_TOP(res);
            if (res == NULL)
                goto error;
            DISPATCH();
        }

This corresponds to the article's description, but it also adds reference counting (the Py_DECREF operations) and error handling. The real work is inside the PyNumber_Multiply function, which must check the operand types and execute the appropriate operation.