randomizer and csv reader

import random
def csv_reader(filename):
    ''' gives back a list of every element in the csv file  '''

    a = []
    try:
        with open(filename, "r") as csvfile:
            for row in csvfile:
                tmp = row.split(";")
                a.append(tmp[0])
    except FileNotFoundError:
        print("Could not find file, please retry.")
        main()
    return a

def randomizer(a:list, y:int) -> (list):
    '''it randomizes the elements in a list into different y different teams'''
    b = [[]]
    for num in range(y):
        b.append([])
    for element in a:
        tmp = (random.randrange(0, y+1))
        b[tmp].append(element)
    return b



def main():
    filename = input("Inserire nome file o path: ")
    if filename[-4:] != '.csv':
        filename = filename + '.csv'
    a = csv_reader(filename)
    y = int(input("Inserire il numero di team: "))
    b = randomizer(a, y)
    print(b)

main()