Debugging python scripts fails

I have a plugin that is launced via python nosetests and i want to debug that library.
The full command i launch is

/usr/bin/python /usr/bin/nosetests /path/to/script.py -v

Running it witout debugger works as expected.
When i try to launch GDB, i got this error:

Cannot open script file /usr/bin/nosetests /path/to/script.py -v:
No such file or directory

Launching this command in debug mode works in Qt Creator 3.2.1