code: def CalculateForecastStats(matched, available, possible=None):
    
    if matched > 0:
      available_percent = (float(available) / matched) * 100.
    else:
      available_percent = 0
  
    if possible is not None:
      if matched > 0:
        possible_percent = (possible/float(matched)) * 100.
      else:
        possible_percent = 0
    else:
      possible_percent = None
  
    return available_percent, possible_percent
docs: Calculate forecast percentage stats.
  
    Args:
      matched: The number of matched impressions.
      available: The number of available impressions.
      possible: The optional number of possible impressions.
  
    Returns:
      The percentage of impressions that are available and possible.