Python: fastest way to create a list of n lists

Question

So I was wondering how to best create a list of blank lists:

[[],[],[]...]

Because of how Python works with lists in memory, this doesn't work:

[[]]*n

This does create [[],[],...] but each element is the same list:

d = [[]]*n
d[0].append(1)
#[[1],[1],...]

Something like a list comprehension works:

d = [[] for x in xrange(0,n)]

But this uses the Python VM for looping. Is there any way to use an implied loop (taking advantage of it being written in C)?

d = []
map(lambda n: d.append([]),xrange(0,10))

This is actually slower. :(

Answer 1

The probably only way which is marginally faster than

d = [[] for x in xrange(n)]

is

from itertools import repeat
d = [[] for i in repeat(None, n)]

It does not have to create a new int object in every iteration and is about 15 % faster on my machine.

Edit: Using NumPy, you can avoid the Python loop using

d = numpy.empty((n, 0)).tolist()

but this is actually 2.5 times slower than the list comprehension.