On 12/13/2011 3:26 PM Kaixi Luo said...
<snip>
Uh, sorry. I made some very bad typos there. It should be:
listA = [[] for i in range(9)]
# some code here...
listB = [[] for i in range(3)]
count = 0
for i in range(3):
for j in range(3):
listB[i].append(listA[count])
count+=1
This yields listB as [[[], [], []], [[], [], []], [[], [], []]]
So, the trick will be that each list element be unique. If you're not
careful, you'll get the same list elements. For example,
listB = [[[]]*3]*3
appears to yield the same result until you append to one of the elements
and discover one of the common early gotcha's:
>>> listB[1][1].append(1)
>>> print listB
[[[1], [1], [1]], [[1], [1], [1]], [[1], [1], [1]]]
To avoid this, each list container needs to be added separately, which
means that the two loops will be required.
You can express it as a single statement using list comprehensions:
>>> listB = [ [ [] for ii in range(3) ] for jj in range(3) ]
>>> listB
[[[], [], []], [[], [], []], [[], [], []]]
>>> listB[1][1].append(1)
>>> listB
[[[], [], []], [[], [1], []], [[], [], []]]
HTH,
Emile
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