Python：如何为嵌套列表返回具有特定格式的字符串

Question

So I am trying to make a text-based adventure game, and it has a map system managed using a nested list, like so:

self.map_ = [
    ['O', 'O', 'O'],
    ['O', 'O', 'O'],
    ['O', 'O', 'O']
]

I have the map inside a class called Map() that has functions to create the map, add and change cells, and so on.

However, I am not sure how to print the map. I would like to create a __str__() function to print the map, but I am unsure of how to do so. I would like it to be printed out like this, with spaces separating the elements on the X axis and a line break separating the Y axis:

O O O
O O O
O O O

I have seen examples that look like this:

for row in map_:
    print ' '.join(row)

...and this example prints the map in exactly the format I would like.

However, I want to turn this into a __str__() function, where it returns a combination of ' '.join(row) (printing a space between each row element) and '\\n'.join(map_) (printing a newline between each row).

Of course, I would like the elements to be in the correct order (upper left on the printed view corresponds to map_[0][0] etc).

Is there a way I can do this with the __str__() function, or do I have to resort to using the printing function above?

Answer 1

How about this, using a list comprehension ?

"\n".join([" ".join(row) for row in map_])

For example:

In [1]: map_ = [
   ...:     ['O', 'O', 'O'],
   ...:     ['O', 'O', 'O'],
   ...:     ['O', 'O', 'O']
   ...: ]

In [2]: print "\n".join([" ".join(row) for row in map_])
O O O
O O O
O O O

And to more directly answer your question about using __str__() :

def __str__(self):
    return "\n".join([" ".join(row) for row in self.map_])

Answer 2

use space to join each row element, and use \\n to join each row

def __str__(self):
    return "\n".join([" ".join(x) for x in self.map_])

Answer 3

Slightly faster solution than the list comprehension approach, though it would only matter at all if the board sizes were huge:

def __str__(self):
    return '\n'.join(map(' '.join, self.map_))

map with a C built-in function (which str.join is) can beat an equivalent list comprehension by a decent margin by pushing more work to the C layer on the CPython reference interpreter.

Answer 4

Try this:

class Map:
    def __init__(self):
        self.map_ = [
            ['O', 'O', 'O'],
            ['O', 'O', 'O'],
            ['O', 'O', 'O']
        ]

    def __str__(self):
        string = ""
        for i in self.map_:
            for j in i:
                string += j + " "
            string += "\n"
        return string

    def change(self, x, y): # For change correctly invert the order
        self.map_[y][x] = "A" 

def main():
    mapa = Map()
    print(mapa)

if __name__ == '__main__':
    main()