我在 python 函数中做错了什么？

Question

def make_str_from_row(board, row_index):

    ''' (list of list of str, int) -> str

    Return the characters from the row of the board with index row_index
    as a single string.

    >>> make_str_from_row([['A', 'N', 'T', 'T'], ['X', 'S', 'O', 'B']], 0)
    'ANTT'
    '''
    for i in range(len(board)):
        i = row_index
        print(board[i])

This prints ['A', 'N', 'T', 'T']

How do I print it like this 'ANTT' instead?

Answer 1

You could simplify that a whole lot by using

>>> def make_str_from_row(board, row_index):
...     print repr(''.join(board[row_index]))
... 
>>> make_str_from_row([['A', 'N', 'T', 'T'], ['X', 'S', 'O', 'B']], 0)
'ANTT'

The reason you get that output is because you print a list since the elements of board are lists. By using join , you get a string.

Also, I don't understand why you use a loop if are going to change the index you loop over.

Answer 2

Well, you got what you told to print!

board is a list of list of str s, so board[i] must be a list of str s, and when you write print(board[i]) , you get a list!

You may need to write this:

print(''.join(board[i]))

Answer 3

I think this was what you were trying to do:

def make_str_from_row(board, row_index):
    ''' (list of list of str, int) -> str

    Return the characters from the row of the board with index row_index
    as a single string.

    >>> make_str_from_row([['A', 'N', 'T', 'T'], ['X', 'S', 'O', 'B']], 0)
    'ANTT'
    '''
    for cell in board[row_index]:
        print cell,