old_contents: from ctypes import Structure,c_uint8,c_uint32
  
  from mbus.MBusDataVariable import MBusDataVariable
  from mbus.MBusDataFixed import MBusDataFixed
  
  class MBusFrameData(Structure):
      _fields_ = [("data_var",   MBusDataVariable),
                  ("data_fixed", MBusDataFixed),
                  ("type",       c_uint32),
                  ("error",      c_uint32)]
  
      def __str__(self):
          return "MBusFrame: XXX"
  
new_contents: from ctypes import Structure,c_uint8,c_uint32
  
  from mbus.MBusDataVariable import MBusDataVariable
  from mbus.MBusDataFixed import MBusDataFixed
  
  class MBusFrameData(Structure):
      _fields_ = [("data_var",   MBusDataVariable),
                  ("data_fixed", MBusDataFixed),
                  ("type",       c_uint32),
                  ("error",      c_uint32)]
  
      def __str__(self):
          return "MBusFrameData: XXX"
  
subject: Correct 'str' representation