how to extract a column from a matrix in python without using any package

Question

I want to find a sum of a column in a matrix without using any package.

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

If I want to extract a row I can write a[i] for ith row, but how to extract a particular column?

Answer 1

So you can get the ith row with a[i] and you can get the nth value from row i with a[i][n] now if you want the column as a whole you will want something like this:

def getColumn(data,col):
    return [k[col] for k in data]

Answer 2

You can access any element :

def sumColumn(m, column):
    sum = 0
    for row in range(len(m)):
        sum += m[row][column]
    return sum

column = 1
print("The sum for column number", column, "is", sumColumn(matrix, column))