code: def binary(self):
      
      dependencies = self.dependencies
      if len(dependencies) != 1:
        raise TargetDefinitionException(self, 'An app must define exactly one binary '
                                              'dependency, have: {}'.format(dependencies))
      binary = dependencies[0]
      if not isinstance(binary, self.binary_target_type()):
        raise TargetDefinitionException(self, 'Expected binary dependency to be a {} '
                                              'target, found {}'.format(self.binary_target_type(),
                                                                        binary))
      return binary
docs: Returns the binary this target references.