docs: def find_usbserial(vendor, product):
    """Find the tty device for a given usbserial devices identifiers.
  
    Args:
       vendor: (int) something like 0x0000
       product: (int) something like 0x0000
  
    Returns:
       String, like /dev/ttyACM0 or /dev/tty.usb...
    """
    if platform.system() == 'Linux':
      vendor, product = [('%04x' % (x)).strip() for x in (vendor, product)]
      return linux_find_usbserial(vendor, product)
    elif platform.system() == 'Darwin':
      return osx_find_usbserial(vendor, product)
    else:
      raise NotImplementedError('Cannot find serial ports on %s'
                                % platform.system())