On Fri, Mar 31, 2017 at 2:49 AM Suresh V. via Python-ideas < python-ideas@python.org> wrote:
> On Thursday 30 March 2017 02:48 PM, Markus Meskanen wrote: > > Hi Pythonistas, > > > > yet again today I ended up writing: > > > > d = [[0] * 5 for _ in range(10)] > > > > And wondered, why don't we have a way to repeat other than looping over > > range() and using a dummy variable? This seems like a rather common > > thing to do, and while the benefit doesn't seem much, something like > > this would be much prettier and more pythonic than using underscore > > variable: > > > > d = [[0] * 5 repeat_for 10] > > Why not: > > d = [[0] * 5 ] * 10 > If you had read the thread before replying, you would have seen that several people have suggested this, and several others have pointed out why it won't work: because that creates a list of 10 references to the SAME five-element list, meaning that mutating d[0] also affects d[1] through d[9] (since each is the same list). The comprehension is necessary to ensure that each element of d is a distinct list.
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