def average(series):
    """
    implements the average of a pandas series from scratch
    suggested functions:
    len(list)
    sum(list)
    you should get the same result as calling .mean() on your series
    https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.Series.mean.html
    See numpy documenation for implementation details:
    https://docs.scipy.org/doc/numpy/reference/generated/numpy.mean.html
    """
    
    return sum(series)/len(series)
    
    pass