[Python3]Многомерные массивы

[Sna1L]

Доброго времени суток.
Сегодня стоокнулся с интересной проблемой...

Приведу пример с интерактивки:

>>>ar = [ [0,0], [0,0] ]
>>>ar
[[0,0], [0,0]] 
>>>ar[0][0] = 1
>>>ar
[[1,0], [0,0]]
>>>
>>>ar = [ [0]*2 ]*2
>>>ar
[[0,0], [0,0]] 
>>>ar[0][0] =1
>>>ar
[[1,0], [1,0]]

Что за фигня??

[Sna1L]

Не выдержал, написал в хелп@питон.орг
Вот ответ(в сокращении):

> >>>ar = [ [0]*2 ]*2
> >>>ar
> [[0,0], [0,0]]
> >>>ar[0][0] =1
> >>>ar
> [[1,0], [1,0]]

In Python, assignment creates a reference. So:

>>> l1=[0]
>>> l2=l1 # l2 now holds another reference to the list
>>> id(l1)
4299723120
>>> id(l2)
4299723120
>>> l1[0]=42
>>> l2
[42]

Similarly, in your example your outer list contains two references to the same inner list. That's what the * operator does.

If you want a copy of a list (or dict, the same thing applies), you can use the copy module. Or you can use a shortcut that falls out of Python's slicing notation:

>>> l3=l1[:]
>>> id(l3)
4299722904

Regards, Matt