Making sure length of matrix row is all the same (python3)

问题

so I have this python 3 code to input a matrix:

matrix = []
lop=True
while lop:
    line = input()
    if not line:
        lop=False
    if matrix != []:
        if len(line.split()) != len(matrix[-1]):
            print("Not same length")
            menu()
    values = line.split()
    row = [int(value) for value in values]
    matrix.append(row)

However,if I enter

1 2 3
4 5 6 7
8 9 0 1 2

my code will let it pass,but you can notice that row 2 and 3 are not same length as row 1; how to prevent that? the row have to be same length as row 1,else it has to return an error message like 'line don't have the same length. I'm not quite sure of how to do that. Maybe:

for row in matrix:
    if len(row) == matrix[1]
        pass
    else:
       print('not same length')

But it doesn't work.

Thanks

回答1:

If you want match the first row length, Try this way,

Use len(matrix[0])

for row in matrix:
    if len(row) == len(matrix[0]):
        pass
    else:
       print('not same lenght')

回答2:

Use the builtin len() function and a break statement.

matrix = []
lop =True
while lop:
    line = input('Enter your line: ')
    if not line:
        lop=False
    if matrix != []:
        if len(line.split()) != len(matrix[-1]):
            print("Not same length")
            break
    values = line.split()
    row = [int(value) for value in values]
    matrix.append(row)

This runs as:

bash-3.2$ python3 matrix.py
Enter your line: 1 2 3
Enter your line: 4 5 6
Enter your line: 7 8 9 0
Not same length
bash-3.2$ 

来源：https://stackoverflow.com/questions/23532218/making-sure-length-of-matrix-row-is-all-the-same-python3