Creating lists of lists in a pythonic way

Question

I\'m using a list of lists to store a matrix in python. I tried to initialise a 2x3 Zero matrix as follows.

mat=[[0]*2]*3

However, when I chang

Answer 1

What about:

m, n = 2, 3
>>> A = [[0]*m for _ in range(n)]
>>> A
[[0, 0], [0, 0], [0, 0]]
>>> A[0][0] = 1
[[1, 0], [0, 0], [0, 0]]

Aka List comprehension; from the docs:

List comprehensions provide a concise way to create lists 
without resorting to use of     
map(), filter() and/or lambda. 
The resulting list definition tends often to be clearer    
than lists built using those constructs.

Answer 2

This one is faster than the accepted answer!
Using xrange(rows) instead of [0]*rows makes no difference.

>>> from itertools import repeat
>>> rows,cols = 3,6
>>> a=[x[:] for x in repeat([0]*cols,rows)]

A variation that doesn't use itertools and runs around the same speed

>>> a=[x[:] for x in [[0]*cols]*rows]

From ipython:

In [1]: from itertools import repeat

In [2]: rows=cols=10

In [3]: timeit a = [[0]*cols for _ in [0]*rows]
10000 loops, best of 3: 17.8 us per loop

In [4]: timeit a=[x[:] for x in repeat([0]*cols,rows)]
100000 loops, best of 3: 12.7 us per loop

In [5]: rows=cols=100

In [6]: timeit a = [[0]*cols for _ in [0]*rows]
1000 loops, best of 3: 368 us per loop

In [7]: timeit a=[x[:] for x in repeat([0]*cols,rows)]
1000 loops, best of 3: 311 us per loop