Python 2.7 无法使用子进程执行py文件

我在Windows7中使用Python2.7。 当我使用subprocess执行py文件时，不会发生错误，subprocess中会返回“success”，但该文件（flashimage.py）实际上没有执行

def program(self):
    self.blueflashcmd = os.path.join('python' + self.TESTENGINEDIR, 
    'flashimage.py')
    args = [self.blueflashcmd]        
    output =  self.my_check_output(args)
    if 'Success' not in output:
        error_msg = output.strip().split('\n')[-1]
        raise ProgramError(error_msg)
def my_check_output(self, args, retry=False):
    start = time.clock()
    p = subprocess.Popen(args, stdout=subprocess.PIPE, 
    stderr=subprocess.STDOUT, startupinfo=suinfo)
    output = ''
    while p.poll() is None:
        part = p.stdout.read()
        output += part
        time.sleep(0.1)
    part = p.stdout.read()
    output += part

    if p.returncode != 0:
        raise ProgramError("RETURN %d: %s" % (p.returncode, 
   output.strip()))

    if not output.strip():
        if not retry:                
            return self.my_check_output(args, retry=True)
        else:               
            raise ProgramError('ERROR')
    return output