"""
Arithmetic mean
Reference: https://en.wikipedia.org/wiki/Arithmetic_mean

Arithmetic series
Reference: https://en.wikipedia.org/wiki/Arithmetic_series
(The URL above will redirect you to arithmetic progression)
"""


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
 >>> is_arithmetic_series(4)
 Traceback (most recent call last):
 ...
 ValueError: Input series is not valid, valid series - [2, 4, 6]
 >>> is_arithmetic_series([])
 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 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])
 4.333333333333333
 >>> 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")
 answer = 0
 for val in series:
 answer += val
 return answer / len(series)


if __name__ == "__main__":
 import doctest

 doctest.testmod()