debug-py-c-extensions's Introduction

Debug Python's C/C++ extensions

You can easily debug Python's C/C++ extensions using GDB/LLDB. Here's a demo.

You need to install pybind11 to build and run this project.

How to build

mkdir build
cmake -S . -B build -DCMAKE_BUILD_TYPE=ON -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
cmake --build build

This will build a hello extension module in build/, e.g. build/hello.cpython-38-darwin.so in macOS.

How to run/debug

main.py is a simple Python script that loads the hello extension module and calls the hello function:

# main.py
import build.hello as hello

hello.hello(42)

Set a breakpoint using VS Code GUI to hello.cpp's hello function, and click the Debug button of VS Code. You can check the debug config: .vscode/launch.json.

You can also use GDB/LLDB CLI to debug it:

lldb python main.py
(lldb) target create "python"
Current executable set to '/Users/guoshuai/mambaforge/envs/mlx-dev-py38/bin/python' (arm64).
(lldb) settings set -- target.run-args  "main.py"
(lldb) b hello.cpp:4
Breakpoint 1: no locations (pending).
WARNING:  Unable to resolve breakpoint to any actual locations.
(lldb) r
Process 24624 launched: '/Users/guoshuai/mambaforge/envs/mlx-dev-py38/bin/python' (arm64)
1 location added to breakpoint 1
Process 24624 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x00000001006d46cc hello.cpython-38-darwin.so`hello(x=42) at hello.cpp:4:6
   1    #include <pybind11/pybind11.h>
   2   
   3    int hello(int x) {
-> 4        x++;
   5        printf("Hello, %d\n", x);
   6        return x;
   7    }
Target 0: (python) stopped.

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