how to create an empty 2d list in python

1#To create an empty 2d list of size n
2l=[]
3for i in range(n):
4	l.append([])
5#To create an 2d list of size rows and columns
6l=[[0 for j in range(len(column))]for i in range(len(row))]

1>>> b = [['a']*3]*3
2>>> b
3[['a', 'a', 'a'], ['a', 'a', 'a'], ['a', 'a', 'a']]
4>>> b[1][1]
5'a'
6>>> b[1][1] = 'b'
7>>> b
8[['a', 'b', 'a'], ['a', 'b', 'a'], ['a', 'b', 'a']]
9

1[[element] * numcols] * numrows