old_contents: """Assignment."""
  
  from . import HDLObject
  from .const import HDLIntegerConstant
  from .expr import HDLExpression
  from .signal import HDLSignal, HDLSignalSlice
  from .concat import HDLConcatenation
  
  
  class HDLAssignment(HDLObject):
      """Signal assignment."""
  
      def __init__(self, signal, value, assign_type='block'):
          """Initialize."""
          if not isinstance(signal, (HDLSignal, HDLSignalSlice)):
              raise TypeError('only HDLSignal, HDLSignalSlice can be assigned')
  
          self.assign_type = assign_type
          self.signal = signal
  
          if isinstance(value, (HDLIntegerConstant,
                                HDLSignal, HDLExpression,
                                HDLSignalSlice, HDLConcatenation)):
              self.value = value
          elif isinstance(value, int):
              self.value = HDLIntegerConstant(value)
          else:
              raise TypeError('only integer, HDLIntegerConstant, '
                              'HDLSignal, HDLExpression, HDLConcatenation '
                              'allowed')
  
      def get_assignment_type(self):
          """Get assignment type."""
          if self.signal.sig_type == 'comb':
              return 'parallel'
          else:
              return 'series'
  
new_contents: """Assignment."""
  
  from . import HDLObject
  from .const import HDLIntegerConstant
  from .expr import HDLExpression
  from .signal import HDLSignal, HDLSignalSlice
  from .concat import HDLConcatenation
  
  
  class HDLAssignment(HDLObject):
      """Signal assignment."""
  
      def __init__(self, signal, value, assign_type='block'):
          """Initialize."""
          if not isinstance(signal, (HDLSignal, HDLSignalSlice)):
              raise TypeError('only HDLSignal, HDLSignalSlice can be assigned')
  
          self.assign_type = assign_type
          self.signal = signal
  
          if isinstance(value, (HDLIntegerConstant,
                                HDLSignal, HDLExpression,
                                HDLSignalSlice, HDLConcatenation)):
              self.value = value
          elif isinstance(value, int):
              self.value = HDLIntegerConstant(value)
          else:
              raise TypeError('only integer, HDLIntegerConstant, '
                              'HDLSignal, HDLExpression, HDLConcatenation '
                              'allowed')
  
      def get_assignment_type(self):
          """Get assignment type."""
          if self.signal.sig_type in ('comb', 'const'):
              return 'parallel'
          else:
              return 'series'
  
subject: use 'const' signal type