new_contents: """
  ARITHMETIC MEAN : https://en.wikipedia.org/wiki/Arithmetic_mean
  
  """
  
  
  def is_arithmetic_series(series: list) -> bool:
      """
      checking whether the input series is arithmetic series or not
  
      >>> is_arithmetic_series([2, 4, 6])
      True
      >>> is_arithmetic_series([3, 6, 12, 24])
      False
      >>> is_arithmetic_series([1, 2, 3])
      True
      """
      if len(series) == 1:
          return True
      common_diff = series[1] - series[0]
      for index in range(len(series) - 1):
          if series[index + 1] - series[index] != common_diff:
              return False
      return True
  
  
  def arithmetic_mean(series: list) -> float:
      """
      return the arithmetic mean of series
  
      >>> arithmetic_mean([2, 4, 6])
      4.0
      >>> arithmetic_mean([3, 6, 9, 12])
      7.5
      >>> arithmetic_mean(4)
      Traceback (most recent call last):
          ...
      ValueError: Input series is not valid, valid series - [2, 4, 6]
      >>> arithmetic_mean([4, 8, 1])
      Traceback (most recent call last):
          ...
      ValueError: Input list is not an arithmetic series
      >>> arithmetic_mean([1, 2, 3])
      2.0
      >>> arithmetic_mean([])
      Traceback (most recent call last):
          ...
      ValueError: Input list must be a non empty list
  
      """
      if not isinstance(series, list):
          raise ValueError("Input series is not valid, valid series - [2, 4, 6]")
      if len(series) == 0:
          raise ValueError("Input list must be a non empty list")
      if not is_arithmetic_series(series):
          raise ValueError("Input list is not an arithmetic series")
      answer = 0
      for val in series:
          answer += val
      return answer / len(series)
  
  
  if __name__ == "__main__":
      import doctest
  
      doctest.testmod()
  
subject: Add arithmetic_mean.py (#4243)