Try new_list = a[0:2] + [a[4]] + a[6:].
Or more generally, something like this:
from itertools import chain
new_list = list(chain(a[0:2], [a[4]], a[6:]))
This works with other sequences as well, and is likely to be faster.
Or you could do this:
def chain_elements_or_slices(*elements_or_slices):
new_list = []
for i in elements_or_slices:
if isinstance(i, list):
new_list.extend(i)
else:
new_list.append(i)
return new_list
new_list = chain_elements_or_slices(a[0:2], a[4], a[6:])
But beware, this would lead to problems if some of the elements in your list were themselves lists.
To solve this, either use one of the previous solutions, or replace a[4] with a[4:5] (or more generally a[n] with a[n:n+1]).