title: pySerial: port only works the first I use it after I power it on
body: <p>I have trouble reading an arbitrary port with pySerial. I can only read the port when the port hasn't been used by any program after it's turned on. Otherwise, I can open the port but ser.inWaiting() returns 0, telling me there is no data in the port buffer.  Actually, I can see data in a port monitor, so why does pySerial gets no data? I am using os x 10.9.5., python 2.7.8 and pySerial 2.7</p>
  
  <p>Here is the code:</p>
  
  <pre><code>def usb():
      ser = serial.Serial('/dev/tty.usbmodem422651', 115200)
      try:
          while True:
              print ser.read(1000)
      except KeyboardInterrupt:
          ser.close()
           exit
  
  
  if __name__ == "__main__":
      testUSB()
  </code></pre>
  
  <p>Thank you for your help!</p>