我正在编写一个小的 python 脚本,它打印出一个行列表,其中行本身是一个字符串列表。这就是函数的作用。它应该将列表作为输入并打印出漂亮的版本,而不实际更改列表。我可以让它打印出正确的输出。但是经过仔细检查,它也会更改原始列表,尽管我在函数中做的第一件事是使用此 grid_copy = grid[:]
问题:脚本将任何 ''
转换为 ' '
尽管我没有修改列表
[['X', 'X', ''], ['', 'O', 'O'], ['O', 'X', '']]
进入:
[X] [X] [ ]
[ ] [O] [O]
[O] [X] [ ]
我不知道是什么导致列表被更改,除了我在开始制作副本时,我没有在哪里引用原始列表。
我添加的一些有用的注释使我的代码更容易理解我所做的事情。如果您运行代码,我还提供了一个测试用例。
def show_grid(grid):
"""
grid: list. A list of lines, where the lines are a list of strings
return: None
Prints the grid out in the classic 3x3
"""
grid_copy = grid[:] # make a copy so we do not want to actually change grid
len_grid = len(grid_copy) # I use this so much, might as well store it
# add whitespaces to make each single spot the same width
len_digits = len(str((len(grid_copy)**2))) # the number of chars wide the highest number is
# modification happens somewhere vvv
for line in range(len_grid):
for char in range(len_grid):
grid_copy[line][char] = str(grid_copy[line][char]).rjust(len_digits) # proper white spaces
# modification happens somewhere ^^^
# add brackets, THIS IS NOT WHERE THE PROBLEM IS
for line in grid_copy:
print('[' + '] ['.join(line)+']\n') # print each symbol in a box
# TESTING TESTING
test_grid = [['X', 'X', ''], ['', 'O', 'O'], ['O', 'X', '']]
print('test_grid before: {}'.format(test_grid))
show_grid(test_grid) # this should not modify test_grid, but it does
print('test_grid after: {}'.format(test_grid))
输出:
test_grid before: [['X', 'X', ''], ['', 'O', 'O'], ['O', 'X', '']]
[X] [X] [ ]
[ ] [O] [O]
[O] [X] [ ]
test_grid after: [['X', 'X', ' '], [' ', 'O', 'O'], ['O', 'X', ' ']]
最佳答案
当您在列表的列表上编写 grid_copy = grid[:]
时,您只是复制最顶层的列表,而不是列表本身的元素。这称为浅拷贝,与深拷贝相对。你应该写
grid_copy = [x[:] for x in grid]
或
grid_copy = copy.deepcopy(grid)
关于Python - 函数更改输入列表,虽然我做了一个副本,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/21640276/