title: convert ascii character to signed 8-bit integer python
body: <p>This feels like it should be very simple, but I haven't been able to find an answer..</p>
  
  <p>In a python script I am reading in data from a USB device (x and y movements of a USB mouse). it arrives in single ASCII characters. I can easily convert to unsigned integers (0-255) using ord. But, I would like it as signed integers (-128 to 127) - how can I do this?</p>
  
  <p>Any help greatly appreciated! Thanks a lot.</p>