code: def read(self, num_bytes, debug_info=None):
          
          if self.debug:
              if not debug_info:
                  debug_info = str(num_bytes)
              sys.stderr.write("%s: READING %s\n" %(
                      self.__class__.__name__,
                      debug_info
                      ))
          res = self.ser.read(num_bytes)
          if self.debug:
              sys.stderr.write("%s: READ %i:\n%s\n" %(
                      self.__class__.__name__,
                      len(res),
                      pyhsm.util.hexdump(res)
                      ))
          self.num_read_bytes += len(res)
          return res
docs: Read a number of bytes from YubiHSM device.