Question

Using Python, what’s the most efficient way to switch the positions of every other element in a list?

For example, I’m trying to get a sequential list of the alphabet with each letter after A switched, like so:

import string
alphabet = string.ascii_uppercase
# ABCDEFGHIJKLMNOPQRSTUVWXYZ

switched_alphabet = do_something_magic(alphabet)
# ACBEDGF... 
# position 1, 3, 2, 5, 4, 7, 6... 

Answer 1

>>> import string
>>> alphabet = list(string.ascii_uppercase)
>>> for i in range(2, len(alphabet), 2):
...     alphabet[i], alphabet[i-1] = alphabet[i-1], alphabet[i]
... 
>>> alphabet
['A', 'C', 'B', 'E', 'D', 'G', 'F', 'I', 'H', 'K', 'J', 'M', 'L', 'O', 'N', 'Q', 'P', 'S', 'R', 'U', 'T', 'W', 'V', 'Y', 'X', 'Z']
>>>