Question

Sometime I write code like this:

a,temp,b = s.partition('-')

I just need to pick the first and 3rd elements. temp would never be used. Is there a better way to do this?

In other terms, is there a better way to pick distinct elements to make a new list?

For example, I want to make a new list using the elements 0,1,3,7 from the old list. The
code would be like this:

newlist = [oldlist[0],oldlist[1],oldlist[3],oldlist[7]]

It’s pretty ugly, isn’t it?

Answer 1

You can use Python’s extended slicing feature to access a list periodically:

>>> a = range(10)
>>> # Pick every other element in a starting from a[1]
>>> b = a[1::2]
>>> print b
>>> [1, 3, 5, 7, 9]

Negative indexing works as you’d expect:

>>> c = a[-1::-2]
>>> print c
>>> [9, 7, 5, 3, 1]

For your case,

>>> a, b = s.partition('-')[::2]