How do you use a variable as an index when slicing strings in Python?

Question

I've been trying to slice two characters out of a string using a loop, but instead of grabbing two characters, it only grabs one.

I've tried:

input[i:i+1]

and

input[i:(i+1)]

but neither seems to work.

How do I use a variable for slicing?

The full routine:

def StringTo2ByteList(input):
    # converts data string to a byte list, written for ascii input only
    rlist = []
    for i in range(0, len(input), 2):
        rlist.append(input[i:(i+1)])
    return rlist

Answer 1

The slice values aren't the start and end characters of the slice, they're the start and end points. If you want to slice two elements then your stop must be 2 greater than your start.

input[i:i+2]

Answer 2

A nice way to remember slice indexing is to think of the numbers as labeling the positions between the elements.

So for example to slice ba you would use fruit[0:2]. When thinking of it this way, things no longer seem counter-intuitive, and you can easily avoid making off-by-one errors in your code.