how to run excel file or macro of excel  from  odoo v8 using a method (button)?

 in python  it work fine:

>>> import os

>>> os.system("start  'path\\file.xls'")

in odoo doesn't work:

def runMacro(self, cr, uid, ids, context=None):
    if os.path.exists("bilan\\bilan.xls"):
        os.system('start  bilan\\bilan.xls')
    else:
        raise osv.except_osv(_('Error!'),
                             _('error msg'))

thanks in advance