Debugging a mixed code of Python/C++ in Visual Studio (VS) Code

I have a code in C++ that is called from a Python file. In order to look at the code and debug it, I use VS Code. I follow the instructions in https://nadiah.org/2020/03/01/example-debug-mixed-python-c-in-visual-studio-code/

However, I stuck in Step5 because when I try to attach GDB to Python, the terminal writes:

Python Exception <class 'ImportError'> This package should not be accessible on Python 3. Either you are trying to run from the python-future src folder or your installation of python-future is corrupted.:
/usr/bin/gdb: warning:
Could not load the Python gdb module from `/usr/share/gdb/python'. Limited Python support is available from the _gdb module. Suggest passing --data-directory=/path/to/gdb/data-directory.

I don't know whether the problem is the launch.jason or not. My launch.json is:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "(gdb) Attach",
            "type": "cppdbg",
            "request": "attach",
            "program": "/home/vj/python/anaconda2-2020.02/bin/python", /* My virtual env */
            "processId": "${command:pickProcess}",
            "MIMode": "gdb",
            "setupCommands": [
                {
                    "description": "Enable pretty-printing for gdb",
                    "text": "-enable-pretty-printing",
                    "ignoreFailures": true
                }
            ]
        },
        {
            "name": "Python: Current File",
            "type": "python",
            "request": "launch",
            "program": "${file}",
            "console": "integratedTerminal"
        }
    ]
}