问题描述
我想定义一个二维数组，而没有这样的初始化长度:
I want to define a two-dimensional array without an initialized length like this:
Matrix = [][]
但它不起作用...
我已经尝试过下面的代码，但这也是错误的:
I've tried the code below, but it is wrong too:
Matrix = [5][5]
错误:
Traceback ...
IndexError: list index out of range
我怎么了?
推荐答案
从技术上讲，您正在尝试索引未初始化的数组.您必须先使用列表初始化外部列表，然后再添加项目.Python 调用这个列表理解".
You're technically trying to index an uninitialized array. You have to first initialize the outer list with lists before adding items; Python calls this"list comprehension".
# Creates a list containing 5 lists, each of 8 items, all set to 0
w, h = 8, 5;
Matrix = [[0 for x in range(w)] for y in range(h)]
您现在可以将项目添加到列表中:
Matrix[0][0] = 1
Matrix[6][0] = 3 # error! range...
Matrix[0][6] = 3 # valid
请注意，矩阵是"y"地址主地址，换句话说，"y索引"位于"x索引"之前.
Note that the matrix is "y" address major, in other words, the "y index" comes before the "x index".
print Matrix[0][0] # prints 1
x, y = 0, 6
print Matrix[x][y] # prints 3; be careful with indexing!
尽管您可以根据需要命名它们，但如果您对内部列表和外部列表都使用"x"，并且希望使用非平方矩阵，那么我会以这种方式来避免索引可能引起的混淆.
Although you can name them as you wish, I look at it this way to avoid some confusion that could arise with the indexing, if you use "x" for both the inner and outer lists, and want a non-square Matrix.
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