将班级人数（比如21）随机分成三组

# random split a list such as the number of a class

import random 


# equal random split a list
def randomEqualSplit(mylist, n):
    resultList = [] # create result list
    part = round(len(mylist)/n) # calculate the part 
    for i in range(n): # for every part 
        extract = random.sample(mylist, part) # extrat one part 
        for i in extract : # for every element 
            if i in extract: # if the element in the list 
                mylist.remove(i) # remove the element form the list
        resultList.append(extract) # add the extract element to a empty list
    return resultList # return the list

result = randomEqualSplit([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21],3) # create the object of the function
print(result) # print the result