code: def screenshot(self, filename, scale=1.0, quality=100):
          '''take screenshot.'''
          result = self.server.screenshot(filename, scale, quality)
          if result:
              return result
  
          device_file = self.server.jsonrpc.takeScreenshot("screenshot.png",
                                                           scale, quality)
          if not device_file:
              return None
          p = self.server.adb.cmd("pull", device_file, filename)
          p.wait()
          self.server.adb.cmd("shell", "rm", device_file).wait()
          return filename if p.returncode is 0 else Nonf screenshot(self, filename, scale=1.0, quality=100):
          '''take screenshot.'''
          result = self.server.screenshot(filename, scale, quality)
          if result:
              return result
  
          device_file = self.server.jsonrpc.takeScreenshot("screenshot.png",
                                                           scale, quality)
          if not device_file:
              return None
          p = self.server.adb.cmd("pull", device_file, filename)
          p.wait()
          self.server.adb.cmd("shell", "rm", device_file).wait()
          return filename if p.returncode is 0 else None
docs: take screenshot.