Is it possible to give a DAP Server example for Python?

[falan]

Could you share an example of setting a DAP server in Python? I've experimented with several configurations using debugpy, but none have been successful. There is a bug in PyCharm's debugger that causes breakpoints to be ignored when using the built-in debugger. However, in VSCode, it successfully stops at breakpoints.

[angelozerr]

Could you explain me how you have tried to configure your dap server please. And give me detail how to install it, the download url

[falan]

Sure, I can connect using this method in VSCode, but it doesn't work with DAP.

1. Install Python and ensure it is properly set up on your system.
2. Use pip install debugpy to install the required debugpy package.
3. Create a test file named "dap_test.py" with a simple Python script that includes a main() function printing "hello world."

def main():
    a = "hello world"
    print(a)


if __name__ == "__main__":
    main()

4. Navigate to the directory containing your test file and execute the following command to start the debug server:
   python -m debugpy --wait-for-client --listen 0.0.0.0:5678 dap_test.py.
   This will make the script wait for a debugger to attach.

5. Open VSCode and add the following configuration to your launch.json file under the .vscode folder:
   • Set the "name" to "Attach."
   • Specify the "type" as "python."
   • Use the "request" type as "attach."
   • Provide the "host" as 127.0.0.1 and the "port" as 5678 to match the debugpy listener.

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Attach",
            "type": "python",
            "request": "attach",
            "connect": {
                "host": "127.0.0.1",
                "port": 5678
            }
        }
    ]
}

6. Once the configuration is added, launch the debugger in VSCode and select the "Attach" configuration. It should connect successfully to the running debugpy server.

This is the setting using DAP.

I hope this helps.

[angelozerr]

Sure, I can connect using this method in VSCode, but it doesn't work with DAP.

1. Install Python and ensure it is properly set up on your system.
2. Use pip install debugpy to install the required debugpy package.
3. Create a test file named "dap_test.py" with a simple Python script that includes a main() function printing "hello world."

def main():
    a = "hello world"
    print(a)


if __name__ == "__main__":
    main()

4. Navigate to the directory containing your test file and execute the following command to start the debug server:
   python -m debugpy --wait-for-client --listen 0.0.0.0:5678 dap_test.py.
   This will make the script wait for a debugger to attach

I think this command is not the proper dap server command. If I understand correctly it launches the dap_test.py and wait for that a dap client connect to the 5678 port.

So this command must be executed with a standard intellij terminal. Once you will start tjis command it will wait for that dap client will connect to the port.

After launching this command in a terminal,, try to fill the dap server command like

python -m debugpy --connect 5678

Or perhaps just with

python -m debugpy --connect

Perhaps it will take your connect config that you have declared in your json?

And run the launch, is it working better?

5. Open VSCode and add the following configuration to your launch.json file under the .vscode folder:
   • Set the "name" to "Attach."
   • Specify the "type" as "python."
   • Use the "request" type as "attach."
   • Provide the "host" as 127.0.0.1 and the "port" as 5678 to match the debugpy listener.

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Attach",
            "type": "python",
            "request": "attach",
            "connect": {
                "host": "127.0.0.1",
                "port": 5678
            }
        }
    ]
}

6. Once the configuration is added, launch the debugger in VSCode and select the "Attach" configuration. It should connect successfully to the running debugpy server.

This is the setting using DAP.

I hope this helps.

[falan]

Thank you for your prompt response.
Unfortunately, it doesn't seem to be working. I started the DAP server through the IntelliJ terminal.

First, I attempted the following steps:

1. Added the port number:
   

2. Added the port number.
   

3. Include the filename
   

with this configuration.

[angelozerr]

@falan stop trying, the DAP support from LSP4IJ cannot manage correctly attach request.

Let me investigate the problem.

[angelozerr]

@falan good news I can debug Python with attach!

I need to do some refactoring to support attach request. I will ping you when it will be available.

[falan]

For your reference, this is one of the most highly requested features for support in PyCharm.
https://youtrack.jetbrains.com/issue/PY-63403/Support-debugpy
https://youtrack.jetbrains.com/issue/PY-73432/Use-a-single-port-for-communication-between-PyCharm-and-the-debugger

[angelozerr]

Thats fantastic for LSP4IJ, thansk for sharing that!

[angelozerr]

@falan I will push soon my work (I need just to clean some code and write doc) but according my test it seems it is working pretty well:

I can debug py file and inline debug value should work:

For the configuration, you must not fill some command, but just fill address and port:

In this screenshot address is filled with $connect.address to retrieve the value from the JSON, but you can fill the real value if you wish. It is the same for port.

Before debugging, you will need to open a terminal and start the debugpy

And after that you can start the DAP configuration with attach and that's it!

The debugpy DAP server supports completion it is super nice:

I will try to pushmy work today once I will write documentation and you will able to test with https://github.com/redhat-developer/lsp4ij?tab=readme-ov-file#testing-nightly-builds

[falan]

It works perfectly. Thank you for your excellent work.

[angelozerr]

Thanks so much for your feedback. I am glad that it works for you.

Could you please help us to promote this DAP support with Python:

• by adding a review at Jetbrains marketplace https://plugins.jetbrains.com/plugin/23257-lsp4ij/reviews
• by speaking about this DAP support with Python in https://youtrack.jetbrains.com/issue/PY-63403/Support-debugpy
  and https://youtrack.jetbrains.com/issue/PY-73432/Use-a-single-port-for-communication-between-PyCharm-and-the-debugger

Thanks so much for your help.

[falan]

I am happy to help promote the DAP support for Python. I will definitely add a review on the JetBrains marketplace and share my feedback on the YouTrack issues.