Debugging Prefect Flows with breakpoints. Hello friends. I love coding Python in VSCode, the debugging with breakpoints make me so efficient. But the debugging fun stops with Prefect Flows, when we initialize them from CLI:

$ prefect run --path myflow.py --log-level INFO --param myparam=val

Here the development flow becomes rather blackboxed/trial-and-error. Is it possible to somehow set breakpoints in VSCode, start a prefect flow from CLI, and attach the debugger to the python process? (Running with the LocalExecutor)

Yes this is possible. You should just be able to add a new python launch configuration with prefect run command and arguments. Another option is to add a call to flow.run in your flow and using the debug current file feature.

Oh yes, I was using a small pytest file with flow.run([params]) but the main guard is also nice.

Here is an example launch config if you wanted to go that route (for instance if you didn’t want the main guard)

{
  "name": "Python: Flow Debug Example",
  "type": "python",
  "request": "launch",
  "program": "${workspaceFolder}/.venv/bin/prefect",
  "args": [
    "run",
    "--path",
    "dev_flows/debug_flow.py"
  ],
  "console": "integratedTerminal",
  "justMyCode": true
}

I think the launch config has the upside to be able to show info/debug logs to the terminal. Or is it also possible with the flow.run() debug method?

Both of them should show them, vs code should create a python debug terminal

@Kevin Mullins thanks a lot, both works great. Launch config is a bit clunkly because prefect is installed with pipenv:

program": "/home/[USER]/.local/share/virtualenvs/[SOURCEFOLDER]-[HASH]/bin/prefect",