code: def set_attribute(self, key, value):
      '''
      Add or update the value of an attribute.
      '''
      if isinstance(key, int):
        self.children[key] = value
      elif isinstance(key, basestring):
        self.attributes[key] = value
      else:
        raise TypeError('Only integer and string types are valid for assigning '
            'child tags and attributes, respectively.'f set_attribute(self, key, value):
      '''
      Add or update the value of an attribute.
      '''
      if isinstance(key, int):
        self.children[key] = value
      elif isinstance(key, basestring):
        self.attributes[key] = value
      else:
        raise TypeError('Only integer and string types are valid for assigning '
            'child tags and attributes, respectively.')
docs: Add or update the value of an attribute.