[Numpy-discussion] initializing an array of lists

Keith Goodman kwgoodman@gmail....
Sun Nov 8 19:33:22 CST 2009


On Sun, Nov 8, 2009 at 5:02 PM, Ravi <lists_ravi@lavabit.com> wrote:
> On Saturday 07 November 2009 22:56:29 alan@ajackson.org wrote:
>> I want to build a 2D array of lists, and so I need to initialize the
>> array with empty lists :
>>
>> myarray = array([[[],[],[]] ,[[],[],[]]])
>
>
> In [1]: [[[]]*3]*2
> Out[1]: [[[], [], []], [[], [], []]]

Have to be careful with that one:

>> x = [[[]]*3]*2
>> x[0][0] = [9999]
>> x
   [[[9999], [], []], [[9999], [], []]]

but not with this one:

>> x = [[[] for i in range(3)] for j in range(2)]
>> x[0][0] = [9999]
>> x
   [[[9999], [], []], [[], [], []]]


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