code: def mean_key(self):
      return f"{self.name}.mean"
  
imports: from abc import ABC
  from typing import Dict, Optional
  import numpy
  from .None import Indicator
  from ...util.values import to_numpy
label_desc: Use image node_id 4 for calling the NumericIndicator obj's underlying member method code with example usage: obj.mean_key() and returns: self, str