Merge pull request #8 from danielenricocahall/add-negative-indexing

Add negative slicing support

Author: btwael

superstring/superstring.py

@@ -73,9 +73,10 @@ def __str__(self):
         return self.toPrintable()
 
     def __getitem__(self, key):
-        # TODO: Negative Indexing
         if isinstance(key, slice):
-            return self.substring(key.start, endIndex = key.stop)
+            start = key.start if key.start > 0 else self.length() + key.start
+            stop = key.stop if key.stop > 0 else self.length() + key.stop
+            return self.substring(start, end_index=stop)
         return self.characterAt(key)
 
 class SuperString(SuperStringBase):