How to use the vscode python debugger with a project built with bazel?

Question

I want to debug a python file which has a few dependencies that only appear in the runfiles from bazel. How can I debug a bazel build with the vscode debugger?

Answer 1

As someone famous said, "Yes, we can".

You would need to use the "ptvsd" python package.

One-time Setup

• Add "ptvsd" as a Python dependency in Bazel
• In VS Code, in your launch.json file, add the following configuration:

{
    "name": "Python: Attach",
    "type": "python",
    "request": "attach",
    "port": 5724,
    "host": "localhost"
},

Debug

When you want to debug a specific file:

• In the Python file you want to debug, add the following lines:

import ptvsd
ptvsd.enable_attach(address=('localhost', 5724), redirect_output=True)
print('Now is a good time to attach your debugger: Run: Python: Attach')
ptvsd.wait_for_attach()

• Run Bazel on this file as you normally would (bazel run :server for instance)
• Execution will stop at "Now is a good time to attach your debugger: Run: Python: Attach"
• In VS Code, click on the "Python: Attach" debug option that we setup earlier:

• That's it!

Feel free to change the port, 5724 in this example.