The numpy array you are defining is not the right shape for the loop you are using. b = np.array([]) gives you an array of shape (0,)

You can use something like np.zeros to define your 2D array.

import numpy as np
b = np.zeros((3,6))
for i in range(2):
    for j in range(5):
        b[i][j]=i+j
print(b)

The output will be

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

Another option is to make a 2D list, fill it up in for loops, and convert to numpy array later

import numpy as np

#2D array
b = [ [0 for _ in range(6)] for _ in range(3)]

#Fill up array with for loops
for i in range(2):
    for j in range(5):
        b[i][j]=i+j

#Convert to numpy array
print(np.array(b))

The output will be

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

It is just a shortcut for this:

x = []
for j in range(column):
    _ = []
    for i in range(row):
        _.append(i)
    x.append(_)

you can put the inner for loop into one by saying that the list is composed of a whole bunch of 0's. We do that for each i in range(row), so we can say _ = [0 for i in range(row)]. This is how that looks:

x = []
for j in range(column):
    x.append([0 for i in range(row)])

We can now see that x is composed of a bunch of [0 for i in range(row)]'s and we do that once for each of j in range(column), so we can simplify it to this:

x = [[0 for i in range(row)] for j in range(column)]

Note this:

>>> matrix = [[0] * 3] * 3
>>> [x for x in matrix]
[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
>>> [id(x) for x in matrix]
[32484168, 32484168, 32484168]
>>>

Three rows but only one object.

See the docs especially Note 2 about the s * n operation.

Fix:

>>> m2= [[0] * 3 for i in xrange(5)]
>>> [id(x) for x in m2]
[32498152, 32484808, 32498192, 32499952, 32499872]
>>>

Update: Here are some samples of code that gets an answer simply (i.e. without iter()):

>>> nrows = 2; ncols = 4
>>> zeroes = [[0 for j in xrange(ncols)] for i in xrange(nrows)]
>>> zeroes
[[0, 0, 0, 0], [0, 0, 0, 0]]
>>> ap = [[ncols * i + j for j in xrange(ncols)] for i in xrange(nrows)]
>>> ap
[[0, 1, 2, 3], [4, 5, 6, 7]]
>>>

Is this what you want?

data = []
for device in devices:
    data.append([device])
    for command in commands:
        ssh = paramiko.SSHClient()
        ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
        ssh.connect(device, username="admin", password="test")
        stdin, stdout, stderr = ssh.exec_command(command)
        output= stdout.read()
        data[-1].append(output)
    data[-1] = tuple(data[-1])

Some explanation:

what data[-1] and tuple(data[-1]) actually do

Note that data is supposed to be a list of tuples.

1. data[-1] refers to the last item of the list data.

2. data[-1] is built as a list in the inner loop. As your specified output structure of data is a list of tuples, the code uses the function tuple() to get a tuple converted from the list data[-1].