我正在写一个小型的python脚本,打印出一行行,列表中的行本身就是一个字符串列表。这是函数的功能。它应该将列表作为输入并打印出漂亮的版本,而不用实际更改列表。我可以打印出正确的输出。但经过仔细检查,它也改变了原来的名单,虽然我在函数做的第一件事就是使用这种grid_copy = grid[:]
Python - 功能改变的输入列表,虽然我做了一个副本
问题使原始列表的副本:该脚本将任何''
到' '
虽然我不修改列表
[['X', 'X', ''], ['', 'O', 'O'], ['O', 'X', '']]
到:
[X] [X] [ ]
[ ] [O] [O]
[O] [X] [ ]
我不知道是什么导致列表被改变,没有我在哪里引用原始列表,除非我在开始复制时。
我的代码包含了几个有用的注释,我添加了这些注释以便更容易理解我所做的事情。如果你运行代码,那么我也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))
OUTPUT:
test_grid before: [['X', 'X', ''], ['', 'O', 'O'], ['O', 'X', '']]
[X] [X] [ ]
[ ] [O] [O]
[O] [X] [ ]
test_grid after: [['X', 'X', ' '], [' ', 'O', 'O'], ['O', 'X', ' ']]
顺便说一下,[链接](http://docs.python.org/2/library/copy.html)仍然有用,它应该始终是您的第一次访问。 – keyser