Why does [-1:-1:-1] not work for reversing a string?
python, slice, string
Solution
s[-1:-1:-1]
Doesn't work for the same reason that
s[0:0]
doesn't give you 'abcd'.
When you slice, you are referring to the space between two elements, not the location of those elements. So you're asking for the space between -1 and -1, which is ''.
Problem
Maybe someone can explain why a particular slice operation to reverse a string doesn't work. There must be something about slices I don't understand. Basic operation: s[start:end:step] Given ``` s='abcd' ``` to reverse this string I can do using default values ``` s[::-1] ``` or ``` s[-1::-1] ``` Those are fine, but why doesn't ``` s[-1:-1:-1] ``` work and give me the whole string reversed? It should start at with the last character in the string at (-1), and the stepsize is -1. It should run down to one before -1 i.e., index 0. Instead I get ''. ``` for i in xrange(3, -2, -1): print 's[-1:%d:-1] => ' %i, print s[-1:i:-1] ``` yields: ``` s[-1:3:-1] => # didn't expect any output s[-1:2:-1] => d s[-1:1:-1] => dc s[-1:0:-1] => dcb s[-1:-1:-1] => # shouldn't this be 'dcba'? ``` what am I missing here? (I did see a lot of posting on reversing strings, but if this particular item was explained somewhere I missed it)