what is del()

Question

a = [8, 0, 4, 6, 1]
del(a[1::3])
print(sum(a))
why #output: 18

Answer 1

del is short for delete.

1::3 means that from position one we delete every third element. So we delete 0 and 1.

Remaining: 18 in sum.

EDIT: Downvote? Seriously? 🤔

Answer 2

Daniel Möhring, basically, the slice syntax is a shortcut for what you would write in a C-ish language with loop variables.

With the first number you set the start point, with the second number the (non-inclusive) end point, with the third the step width and direction. So by 10::-2 you'd move backwards from 10, skipping one.

Also by using negative numbers, you have a shortcut to count from the end of an iterable: -1 is the last element, -2 the second last and so on.

1 to 3 would simply be [1:4]. (If you think in C: (i=1; i<4; ++i))

Answer 3

Daniel Möhring, in the beginning it may be confusing, but after you got used to the patterns, you can read them easily and don't want to miss them.

array[::2] # every even index
array[1::2] # every odd
array[::-1] # array backwards
array[:-3] # array without the
# two final elements
array[:] # shallow copy of
#a whole array

and so on.

Combine that with 'comprehensions' and you can often write in one line, what would be a whole block in C-ish languages.

Answer 4

*del is a tag which shows the deleted text. It is no longer supported in HTML5*

Its about python bro ;)

Answer 5

HonFu btw what would it be in python to address the range 1-3?

Answer 6

HonFu That seems kinda hard to read imo

I mean these short forms are propably easier to write but for understanding purpose you can get quite confused i think.

Answer 7

HonFu I definetely need to give python a try some day ^^ Very interesting language