len_slice: Support sequences of integer indices.

Adds support for sequences of integer indices. Normalizes their values
to ensure they are all valid first. Then simply counts how many integer
indices are present to get their length.

kenjutsu/kenjutsu.py

@@ -317,18 +317,22 @@ def len_slice(a_slice, a_length=None):
 
     new_slice = reformat_slice(a_slice, a_length)
 
-    if new_slice.stop is None:
-        if new_slice.step > 0:
-            raise UnknownSliceLengthException(
-                "Cannot determine slice length without a defined end point. " +
-                "The reformatted slice was " + repr(new_slice) + "."
-            )
-        else:
-            new_slice = slice(new_slice.start, -1, new_slice.step)
+    new_slice_size = 0
+    if isinstance(new_slice, slice):
+        if new_slice.stop is None:
+            if new_slice.step > 0:
+                raise UnknownSliceLengthException(
+                    "Cannot determine slice length without a defined end"
+                    " point. The reformatted slice was %s." % repr(new_slice)
+                )
+            else:
+                new_slice = slice(new_slice.start, -1, new_slice.step)
 
-    new_slice_diff = float(new_slice.stop - new_slice.start)
+        new_slice_diff = float(new_slice.stop - new_slice.start)
 
-    new_slice_size = int(math.ceil(new_slice_diff / new_slice.step))
+        new_slice_size = int(math.ceil(new_slice_diff / new_slice.step))
+    else:
+        new_slice_size = len(new_slice)
 
     return(new_slice_size)