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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 ApproximateDistanceBetweenStops(stop1, stop2):
 """Compute approximate distance between two stops in meters. Assumes the Earth is a sphere."""

  if (stop1.stop_lat is None or stop1.stop_lon is None or
      stop2.stop_lat is None or stop2.stop_lon is None):
    return None
  return ApproximateDistance(stop1.stop_lat, stop1.stop_lon,
                             stop2.stop_lat, stop2.stop_lon)