old_contents: class SimilarityMetric(object):
      _FMT = "{name}[{fixed}, {moving}, {opts}]"
  
      def __init__(self, name, *opts):
          self.name = name
          self.opts = opts
  
      def format(self, fixed, moving, weight=1):
          """
          Formats the ANTS similiarity metric argument.
  
          :param reference: the fixed reference file
          :param moving: the moving file to register
          :param weight: the weight to assign this metric (default 1)
          :rtype: str
          """
          opts = [weight]
          opts.extend(self.opts)
          opt_arg = ', '.join(opts)
          return SimilarityMetric._FMT.format(name=self.name, fixed=fixed, moving=moving, opts=opt_arg)
  
      def __str__(self):
          return self.name
  
  
  class PR(SimilarityMetric):
      """
      The probability mapping metric.
      """
  
      def __init__(self):
          super(PR, self).__init__('PR')
  
  
  class CC(SimilarityMetric):
      """
      The cross-correlation metric.
      """
  
      def __init__(self, radius=4):
          super(CC, self).__init__('CC', radius)
  
  
  class MI(SimilarityMetric):
      """
      The mutual information metric.
      """
  
      def __init__(self, bins=32):
          super(MI, self).__init__('MI', bins)
  
  
  class MSQ(SimilarityMetric):
      """
      The mean-squared metric.
      """
  
      def __init__(self):
          super(MSQ, self).__init__('MSQ', 0)
  
  
  class JTB(SimilarityMetric):
      """
      The B-spline metric.
      """
  
      def __init__(self, radius=32):
          super(JTB, self).__init__('JTB', radius)
  
new_contents: class SimilarityMetric(object):
      _FMT = "{name}[{fixed}, {moving}, {opts}]"
  
      def __init__(self, name, *opts):
          self.name = name
          self.opts = opts
  
      def format(self, fixed, moving, weight=1):
          """
          Formats the ANTS similiarity metric argument.
  
          :param reference: the fixed reference file
          :param moving: the moving file to register
          :param weight: the weight to assign this metric (default 1)
          :rtype: str
          """
          opts = [weight]
          opts.extend(self.opts)
          opt_arg = ', '.join([str(opt) for opt in opts])
          return SimilarityMetric._FMT.format(name=self.name, fixed=fixed, moving=moving, opts=opt_arg)
  
      def __str__(self):
          return self.name
  
  
  class PR(SimilarityMetric):
      """
      The probability mapping metric.
      """
  
      def __init__(self):
          super(PR, self).__init__('PR')
  
  
  class CC(SimilarityMetric):
      """
      The cross-correlation metric.
      """
  
      def __init__(self, radius=4):
          super(CC, self).__init__('CC', radius)
  
  
  class MI(SimilarityMetric):
      """
      The mutual information metric.
      """
  
      def __init__(self, bins=32):
          super(MI, self).__init__('MI', bins)
  
  
  class MSQ(SimilarityMetric):
      """
      The mean-squared metric.
      """
  
      def __init__(self):
          super(MSQ, self).__init__('MSQ', 0)
  
  
  class JTB(SimilarityMetric):
      """
      The B-spline metric.
      """
  
      def __init__(self, radius=32):
          super(JTB, self).__init__('JTB', radius)
  
subject: Simplify option formatting.