Surprised by the command "del"
steve at holdenweb.com
Sat Mar 1 21:01:51 CET 2008
K Viltersten wrote:
> I'm reading the docs and at 5.2 the del
> statement is discussed. At first, i thought
> i've found a typo but as i tried that
> myself, it turns it actually does work so.
> a = ["alpha", "beta", "gamma"]
> del a[2:2]
> Now, i expected the result to be that the
> "beta" element has been removed. Obviously,
> Python thinks otherwise. Why?!
> I wonder why such an unintuitive effect has
> been implemented. I'm sure it's for a very
> good reason not clear to me due to my
> ignorance. Alternatively - my expectations
> are not so intuitive as i think. :)
It deletes all the elements referred to by the slice. But since 2-2==0,
there are zero elements in the slice, and the list is unchanged when all
zero of them have been deleted:
>>> a = ["alpha", "beta", "gamma"]
You would have got the result you expected with
Remember that slices are specified as half-open intervals. So a[m:n]
includes m-n elements, those indexed from m to n-1.
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC http://www.holdenweb.com/
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