Question

Not sure where I picked this up, but it stuck and I use it all the time.

Can someone explain how this string reversal works? I use it to test for palindromic strings without converting it to a mutable type first.

>>> word = "magic"
>>> magic = word[::-1]
>>> magic
'cigam' 

I would put my best guess, but I don’t want to walk in with any preconceptions about the internals behind this useful trick.

Answer 1

The slice notation goes like this:

my_list[start:end:step]

So, when you do [::-1], it means:

• start: nothing (default)
• end: nothing (default)
• step: -1 (descendent order)

So, you’re going from the end of the list (default) to the first element (default), decreasing the index by one (-1).

So, as many answers said, there is no sorting nor in-place swapping, just slice notation.