Accessing multidimensional matrices in python

Question

sumc=0
t = int(input())
while t :
    x = input().split()
    n = int(x[0])
    k = int(x[1])
    e = int(x[2])
    m = int(x[3])
    suma = [0]*(n-1)
    Matrix = []
    for i in range(n-1):
        Matrix.append([])
        for j in range(e):
            p = int(input())
            Matrix[i].append(p)
    for i in range(n-1):
        for j in range(e):
            suma[i] = suma[i] + Matrix[i][j]
    for j in range(e):
        p = int(input())
        Matrix[n-1][j].append(p)
    suma.sort(suma,suma+(n-1))
    for j in range(e-1):
        sumc  = sumc + Matrix[n-1][j]
    for z in range(m+1):
        if(suma[k-1] < sumc+z):
            break
    if (z==m+1):
        print("imposible")
    else:
        arr[n-1][e-1] = z
        print(arr[n-1][e-1])
    t-=1

I want to access array by keeping one parameter/row/column (here row represented by (n-1), in line 21) constant. But getting error "index out of range". In general, how to access arrays for such type of problems where one of the parameters is/are constant.

Traceback (most recent call last):
  File "C:/Users/User/untitled/cde_chf_entexam.py", line 21, in <module>
    Matrix[n-1][j].append(p)
IndexError: list index out of range

Process finished with exit code 1

JUST SEE THE LINE 20-21 FOR THE ERROR, WHOLE CODE IS NOT NECESSARY, IT'S POSTED IF IT MIGHT HELP

Answer 1

Your loop:

for i in range(n-1):
    Matrix.append([])
    for j in range(e):
        p = int(input())
        Matrix[i].append(p)

adds n-1 elements to Matrix. Since python is 0 indexed, this means that the highest index in Matrix is n-2.

When you do: Matrix[n-1][j].append(p), the expression Matrix[n-1] will fail with an IndexError because n-1 is one higher than the highest indexible location (n-2).

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As an aside, lists of lists are valid data structures for storing matrices in pure python, but there are 3rd party libraries dedicated to making matrices easier to work with. The de-facto standard in this area is numpy.