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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _GetMetric(self, metric_name):
 """Fetches the metric object corresponding to the given name."""

    if metric_name in self._counter_metrics:
      return self._counter_metrics[metric_name]
    elif metric_name in self._event_metrics:
      return self._event_metrics[metric_name]
    elif metric_name in self._gauge_metrics:
      return self._gauge_metrics[metric_name]
    else:
      raise ValueError("Metric %s is not registered." % metric_name)