old_contents: class ExternalManager(object):
      """
      Manager the active externals
      """
      def __init__(self, processors=None, optimizers=None):
          self.processors = processors if processors is not None else []
          self.optimizers = optimizers if optimizers is not None else []
  
      def _register(self, external, externals):
          externals.insert(0, external)
  
      def clear(self):
          """
          Clear this manager
          """
          self.processors = []
          self.optimizers = []
  
      def register_processor(self, processor):
          """
          Add a new processor to the list of processors
          This processor will be added with maximum priority
          """
          self._register(processor, self.processors)
  
      def register_optimizer(self, optimizer):
          """
          Add a new optimizer to the list of optimizer
          This optimizer will be added with maximum priority
          """
          self._register(optimizer, self.optimizers)
new_contents: class ExternalManager(object):
      """
      Manager the active externals
      """
      def __init__(self, processors=None, optimizers=None):
          self.processors = processors if processors is not None else []
          self.optimizers = optimizers if optimizers is not None else []
  
      def _register(self, external, externals):
          externals.insert(0, external)
  
      def _deregister(self, external, externals):
          externals.remove(external)
  
      def clear(self):
          """
          Clear this manager
          """
          self.processors = []
          self.optimizers = []
  
      def register_processor(self, processor):
          """
          Add a new processor to the list of processors
          This processor will be added with maximum priority
          """
          self._register(processor, self.processors)
  
      def deregister_processor(self, processor):
          """
          Remove an existing processor from the list
          Will raise a ValueError if the processor is not present
          """
          self._deregister(processor, self.processors)
  
      def register_optimizer(self, optimizer):
          """
          Add a new optimizer to the list of optimizer
          This optimizer will be added with maximum priority
          """
          self._register(optimizer, self.optimizers)
  
      def deregister_optimizer(self, processor):
          """
          Remove an existing optimizer from the list
          Will raise a ValueError if the optimizer is not present
          """
          self._deregister(processor, self.optimizers)
  
subject: Add option to unregister externals