如何在python中添加或减少任意数量的矩阵

Question

我一直在网上搜索，我似乎无法找到如何回答我的作业问题。用户应输入矩阵并指示是要添加还是减去矩阵。您应该能够根据需要添加或减少任意数量的矩阵，而无需重新输入先前的解决方案。我是python的初学者，我不知道该怎么做。到目前为止，我所拥有的只是

    #Ask the user to input a matrix
    print ('Enter your row one by one (pressing enter between each row). 
    To terminate, enter an empty row.')
    M = []

    #Allow them to determine dimensions
    while True:
        r = input ('Next row > ')
        if not r.strip (): # Empty input
            break
        M.append(list(map(int, r.split())))

    #Display the matrix
    print('M =', M)