make 2d list in python code example

Example 1: how to create 2d list in python

o=[]
for i in range(0,rows):
    x=[]
    for j in range(0,cols):
        x.append(0)
    o.append(x)
#if you use [[0]*cols]*rows all rows will become the same list
#so editing in one row will edit all rows

Example 2: print 2d list in one line

import itertools
arr = [[1, 2, 3], [3, 4, 5]]
res = list(itertools.chain(*arr))
print(" ".join(map(str, res)))
1 2 3 3 4 5