code: def mutateDefault(self, node):
      for field in node._fields:
          value = getattr(node, field)
          if isinstance(value, (list, tuple)):
              for i, item in enumerate(value):
                  if isinstance(item, _ast.AST):
                      new_item = self.mutate(item)
                      if new_item is not None:
                          value[i] = new_item
                  else:
                      pass
  
          elif isinstance(value, _ast.AST):
              new_value = self.mutate(value)
              if new_value is not None:
                  setattr(node, field, new_value)
  
      return None
  
file_path: turicreate/src/python/turicreate/meta/asttools/visitors/__init__.py
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import _ast
label_desc: Use image node_id 1 for calling the Mutator obj's underlying member method code with example usage: obj.mutateDefault(node) and returns: None