class_docstr: A MetricGroup is a named container for metrics and further metric subgroups.
  
  Instances of this class can be used to register new metrics with Flink and to create a nested
  hierarchy based on the group names.
  
  A MetricGroup is uniquely identified by it's place in the hierarchy and name.
  
  .. versionadded:: 1.11.0
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docstr: Creates a new MetricGroup and adds it to this groups sub-groups.
  
  If extra is not None, creates a new key-value MetricGroup pair.
  The key group is added to this group's sub-groups, while the value
  group is added to the key group's sub-groups. In this case,
  the value group will be returned and a user variable will be defined.
  
  .. versionadded:: 1.11.0
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code: def add_group(self, name: str, extra: str = None) -> "MetricGroup":
      """
      Creates a new MetricGroup and adds it to this groups sub-groups.
  
      If extra is not None, creates a new key-value MetricGroup pair.
      The key group is added to this group's sub-groups, while the value
      group is added to the key group's sub-groups. In this case,
      the value group will be returned and a user variable will be defined.
  
      .. versionadded:: 1.11.0
      """
      pass
  
imports: from abc import ABC, abstractmethod
  from typing import Callable
label_desc: Use image node_id 1 for calling the MetricGroup obj's underlying member method code with example usage: obj.add_group(name, extra) without return types