Python - best way to set a column in a 2d array to a specific value

Question

I have a 2d array, I would like to set a column to a particular value, my code is below. Is this the best way in python?

rows = 5
cols = 10

data = (rows * cols) *[0]
val = 10
set_col = 5

for row in range(rows):
    data[row * cols + set_col - 1] = val

If I want to set a number of columns to a particular value , how could I extend this

I would like to use the python standard library only

Thanks

Answer 1

A better solution would be:

data = [[0] * cols for i in range(rows)]

For the values of cols = 2, rows = 3 we'd get:

data = [[0, 0],
        [0, 0],
        [0, 0]]

Then you can access it as:

v = data[row][col]

Which leads to:

val = 10
set_col = 5

for row in range(rows):
    data[row][set_col] = val

Or the more Pythonic (thanks J.F. Sebastian):

for row in data:
    row[set_col] = val

Answer 2

NumPy package provides powerful N-dimensional array object. If data is a numpy array then to set set_col column to val value:

data[:, set_col] = val

Complete Example:

>>> import numpy as np
>>> a = np.arange(10)
>>> a.shape = (5,2)
>>> a
array([[0, 1],
       [2, 3],
       [4, 5],
       [6, 7],
       [8, 9]])
>>> a[:,1] = -1
>>> a
array([[ 0, -1],
       [ 2, -1],
       [ 4, -1],
       [ 6, -1],
       [ 8, -1]])