async def __call__(self, device):
        """
        Invoke the subprocess to ask the user to enter a password for unlocking
        the specified device.
        """
        attrs = {attr: getattr(device, attr) for attr in self.used_attrs}
        attrs.update(self.extra)
        argv = [arg.format(**attrs) for arg in self.argv]
        try:
            stdout = await exec_subprocess(argv)
        except subprocess.CalledProcessError:
            return None
        return stdout.rstrip('\n')
async def __call__ ( self , device ) : attrs = { attr : getattr ( device , attr ) for attr in self . used_attrs } attrs . update ( self . extra ) argv = [ arg . format ( ** attrs ) for arg in self . argv ] try : stdout = await exec_subprocess ( argv ) except subprocess . CalledProcessError : return None return stdout . rstrip ( '\n' )
Invoke the subprocess to ask the user to enter a password for unlocking
        the specified device.