如何构建5x5矩阵？

Question

How can I construct a matrix with 5 rows and 5 columns?

lst = [1,2,3,4,5]

[[float("inf")]*len(lst) for k in range (len(lst))]

gives me [[inf, inf, inf, inf, inf], [inf, inf, inf, inf, inf], [inf, inf, inf, inf, inf], [inf, inf, inf, inf, inf], [inf, inf, inf, inf, inf]]

How can I change the parameters so I can get a 5x5 matrix?

Answer 1

I'm not sure why you are using the lst variable, but what you need is something approaching this:

def matrix(x,y,initial):
    return [[initial for i in range(x)] for j in range(y)]

Which gives:

> print matrix(5,5,float('inf'))
[[inf, inf, inf, inf, inf], [inf, inf, inf, inf, inf], [inf, inf, inf, inf, inf], [inf, inf, inf, inf, inf], [inf, inf, inf, inf, inf]]

> my_matrix = matrix(2,2,0)
> print my_matrix
[[0, 0], [0, 0]]
> my_matrix[0][2] = 2
> print my_matrix
[[0, 2], [0, 0]]

A matrix in most languages is just a set of nested arrays. If you need anything more than that you might want to make a custom class.

Answer 2

What you have already is a 5x5 matrix. Just represented as a list of rows. If you want something that "looks" like a matrix, maybe you'll like numpy:

>>> import numpy as np
>>> np.full((5, 5), np.inf)
array([[ inf,  inf,  inf,  inf,  inf],
       [ inf,  inf,  inf,  inf,  inf],
       [ inf,  inf,  inf,  inf,  inf],
       [ inf,  inf,  inf,  inf,  inf],
       [ inf,  inf,  inf,  inf,  inf]])