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I’m working with VLLM (open-source) which includes C++ extension code compiled for Python. I installed it using

CXXFLAGS="-Og -g" pip install -e .

I want to debug the C++ code from Python by attaching a debugger to the running Python process. I can step into functions, but when I try to inspect local variables, I see messages like d = value has been optimized out

Additionally, compilation is quite slow, and I want to know how to speed up rebuilds after making changes to C++ files.

My questions:

  1. How can I correctly debug the C++ code (via gdb) from Python and see all local variables?

  2. Are there flags or approaches to reduce compile time during development, without losing debugging capabilities?

Environment:

  • Python 3.11
  • Linux Ubuntu 24.04
  • VLLM from source
  • pip installation from source (pip install -e .)
  • Compiler: GCC 12.3.0 (used to build VLLM C++ extensions)

Any guidance on best practices for debugging Python extensions written in C++ and improving the development workflow would be appreciated.

Improve this question
1
  • If you don't want these value has been optimized out, then you have to use -O0 instead of -Og. See here. Commented Sep 17 at 21:44
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