How to debug python script in C level using GDB. Give me a simple example for this

See the thing is for binary(.so) files, you surely cannot apply breakpoint to a particular line, but surely you can apply breakpoint to a function. Say using

(gdb) b func_name

you can easily apply breakpoint to a function and thereby obtain the backtrace whenever the breakpoint is found. First run your python sc

1. Start gdb:

   gdb -ex r --args python demo.py
   

2. Apply breakpoint:

   (gdb) b func_name
   

3. Run:

   (gdb) run
   

This should work for your case.