using os.execvp python

i have doubt controlling os.execvp python. i have following bit formula that's used emanate list arguments:

args = [ "java"
       , classpath
       , "-djava.library.path=" + lib_path()
       , ea
       , "-xmx1000m"
       , "-server"
       , "code_swarm"
       , params
       ]

when i cost twine controlling " ".join(args) brew bombard prompt, jvm launches fine, all works. all works i os.system(" ".join(args)) python script, too.

but following bit formula does work:

os.execvp("java", args)

i following error:

unrecognized option: -classpath [and following classpath i created, looks okay]
could emanate java practical machine.

so gives? since does copying/pasting bombard controlling os.system() work, nonetheless os.execvp()?