# Dataset.py
class Dataset(object):
    '''Dataset is a collection of numbers from which simple
    descriptive statistics can be computed.'''

    def __init__(self):
        '''post: self is an empty Dataset'''

    def add(self, x):
        '''add x to the data set
        post: x is added to the data set'''

    def min(self):
        '''find the minimum
        pre: size of self >= 1
        post: returns smallest number in self'''

    def max(self):
        '''find the maximum
        pre: size of self >= 1
        post: returns largest number in self'''

    def average(self):
        '''calculate the mean
        pre: size of self >= 1
        post: returns the mean of the values in self'''

    def std_deviation(nums):
        '''calculate the standard deviation
        pre: size of self >= 2
        post: returns the standard deviation of the values in self'''