Converting List of String to Integer

[Samir]

Hi Everyone,

I am relatively new to Python so please forgive me for what seems like
a basic question.

Assume that I have a list, a, composed of nested lists with string
representations of integers, such that

a = [['1', '2'], ['3'], ['4', '5', '6'], ['7', '8', '9', '0']]

I would like to convert this to a similar list, b, where the values
are represented by integers, such as

b = [[1, 2], [3], [4, 5, 6], [7, 8, 9, 0]]

I have unsuccessfully tried the following code:

n = []
for k in a:
    n.append([int(v) for v in k])
print n

Does anyone know what I am doing wrong?

Thanks in advance.

Samir