initialized list: strange behavior

[alexander . genkin]

Hi Python experts! Please explain this behavior:

>>> nn=3*[[]]
>>> nn
[[], [], []]
>>> mm=[[],[],[]]
>>> mm
[[], [], []]

Up till now, 'mm' and 'nn' look the same, right? Nope!

>>> mm[1].append(17)
>>> mm
[[], [17], []]
>>> nn[1].append(17)
>>> nn
[[17], [17], [17]]

???

Python 2.5 Win XP

Thanks!
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Re: initialized list: strange behavior

[alexander . genkin]

The issue is exhausted in Python Library Reference, Chapter 3.6, so I
should apologize for initial posting. All comments were helpful,
though Arnaud and Steve are right that pass-by-anything is off the
point.

Thanks All!

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