Python Question

[mell0]

I'm teaching myself how to program in Python. I've never programmed before, so forgive me for my stupidity. Here's the code that I'm trying to figure out (from a book that I'm using):

def reverse(s):
    if s == "":
        return s
    else:
        return reverse(s[1:]) + s[0]

I understand that the string's being sliced, but I can't figure out how each element of the string is returned in reverse order. Recursion sucks.

 

[Mr_Superstar]

Recursion is surprisingly simple once you get used too it.

A simple way to figure it out is to basically "trace" the method step by step.

Take the following method call:

reverse("blah")

At the point of the return statement, you'll have:

return reverse("lah") + "b"

If you follow this again, you'll have:

return (return reverse("ah") + "l") + "b"

Eventually, your call stack will end up like this:

return (return (return (return (return "") + "h") + "a") + "l") + "b"

Now, you can basically see you have this:

"" + "h" + "a" + "l" + "b"

which equals "halb".

 

[Empyrean]

Genius.

Only downside to recursion is the large stack buildup.

But algorithmically, it is beautiful.

 

[deuce868]

In later python versions:

reversed_string = s[::-1]