Taking a screenshot of a device display, then copy it to your computer.

def screencap_exec(self, filename: _PATH = 'screencap.png') -> None:
        '''Taking a screenshot of a device display, then copy it to your computer.'''
        self._execute('-s', self.device_sn, 'exec-out',
                      'screencap', '-p', '>', filename, shell=True)