[issue1408] Inconsistence in multiply list

[Georg Brandl]

Georg Brandl added the comment:

I'm sorry, this is no bug. List multiplication works by referencing,
there is no way to implement it differently in a straightforward way.

Note that in
>>> [a[:]] + [a[:]]
the expression "a[:]" is evaluated twice, yielding two independent
copies of a. In contrast,
>>> [a[:]] * 2
evaluates "a[:]" only once, before the list multiplication is done.
Because of the same reason,
>>> [deepcopy(a)] * 2
doesn't work as you want.

One way to do what you have in mind is
>>> [a[:] for i in range(2)]
which evaluates the "a[:]" once for each iteration of the list
comprehension loop.

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nosy: +georg.brandl
resolution:  -> invalid
status: open -> closed

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