[Python-ideas] Way to repeat other than "for _ in range(x)"

[Jonathan Goble]

On Fri, Mar 31, 2017 at 2:49 AM Suresh V. via Python-ideas <
python-ideas at 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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