[CheckIO] Median

1. Problem: py.checkio.org/en/mission/median/
2. My solution: 

def checkio(data: List[int]) -> [int, float]:
    dummy = sorted(data)
    len_list = len(dummy)
    # For odd elements 
    if len_list % 2 == 1: return dummy[len_list // 2]
    # For even elements 
    else: return (dummy[len_list // 2 - 1] + dummy[len_list // 2]) / 2