Matrix MxN, fill vector with matrix values.

You can do it first install numpy

pip install numpy

Then:

# -*- coding: utf-8 -*-

import numpy as np

n = int(input("Ingrese el numero de fila: \n"))
m = int(input("Ingrese el numero de columna: \n"))

matriz = np.random.randint(0, 100, size=(n, m))
print(matriz)

You have to use append to define the matrix and assign its values to it. For example:

import random
n = 4
m = 3
#a = n*m
matriz = []

for i in range(n):
    matriz.append([])
    for j in range(m):
        matriz[i].append(random.randint(0, 100))

print(matriz)

Exit:

$python main.py
[[7, 78, 57], [18, 3, 58], [30, 44, 17], [45, 39, 64]]

In this way, you are adding to the matrix the number of rows with the first for ( matriz.append([]) ), and then you are adding the elements of the columns with the second for ( matriz[i].append(elemento) ). It's a summary, first you have to add row by row, and then, for each row added, you add the elements of the columns.

It will be out of range because the variable matrix is an empty list, if you say matrix [0] [0] it is not defined unless it is a list of lists.

One way to create an array is this:

import random
a=[]
filas=5
columnas=4
for i in range(filas):
    a.append([])
    for j in range(columnas):
        a[i].append(random.randrange(100))

print(a)

But there is a more compact and practical way to create a matrix:

a=[[i for i in range(6)]for j in range(4)]

whose result is this:

[[0, 1, 2, 3, 4, 5], [0, 1, 2, 3, 4, 5], [0, 1, 2, 3, 4, 5], [0, 1, 2, 3, 4, 5]]