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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 _measurements(session_group, metric_name):
 """A generator for the values of the metric across the sessions in the group. Args: session_group: A SessionGroup protobuffer. metric_name: A MetricName protobuffer. Yields: The next metric value wrapped in a _Measurement instance. """

  for session_index, session in enumerate(session_group.sessions):
    metric_value = _find_metric_value(session, metric_name)
    if not metric_value:
      continue
    yield _Measurement(metric_value, session_index)