> Could not trace the inferior process.

Your issue doesn't seem to be related to Python, but more to gdb in general.

Can you try very basic commands like:

$ gdb -args python3 -c pass
(gdb) run
Starting program: /usr/bin/python3 -c pass
[Inferior 1 (process 20811) exited normally]
(gdb) quit

Or more advanced cases like:

vstinner@apu$ gdb -args ./python Lib/test/gdb_sample.py
(gdb) b builtin_id
Breakpoint 1 at 0x4dd7d0: file Python/bltinmodule.c, line 1205.
(gdb) run
Starting program: /home/vstinner/prog/python/master/python Lib/test/gdb_sample.py

Breakpoint 1, builtin_id (self=0x7ffff7fc0c28, v=42)
    at Python/bltinmodule.c:1205
1205	    return PyLong_FromVoidPtr(v);
(gdb) py-bt
Traceback (most recent call first):
  <built-in method id of module object at remote 0x7ffff7fc0c28>
  File "Lib/test/gdb_sample.py", line 10, in baz
    id(42)
  File "Lib/test/gdb_sample.py", line 7, in bar
    baz(a, b, c)
  File "Lib/test/gdb_sample.py", line 4, in foo
    bar(a, b, c)
  File "Lib/test/gdb_sample.py", line 12, in <module>
    foo(1, 2, 3)
(gdb) quit
A debugging session is active.
Quit anyway? (y or n) y