Restrict to one integral sequence per slice

There are a lot of subtle cases when support multiple integral
sequences, which we are not currently supporting correctly. So as to
avoid potentially providing an incorrect result, simply raise an
exception if multiple integral sequences show up in a slices and note
that only one is supported in a slice. Hopefully we can fix this and
relaxing this constraint in the future.

kenjutsu/format.py

@@ -282,4 +282,13 @@ def reformat_slices(slices, lengths=None):
 
         new_slices = tuple(new_slices)
 
+    n_seqs = sum(map(
+        lambda i: isinstance(i, collections.Sequence), new_slices
+    ))
+    if n_seqs > 1:
+        raise ValueError(
+            "Only one integral sequence supported."
+            " Instead got `%s`." % str(n_seqs)
+        )
+
     return(new_slices)

tests/test_format.py

@@ -298,6 +298,16 @@ def test_reformat_slices(self):
             "Only one Ellipsis is permitted. Found multiple."
         )
 
+        with self.assertRaises(ValueError) as e:
+            format.reformat_slices(
+                ([0, 1], [0, 1]),
+            )
+
+        self.assertEqual(
+            str(e.exception),
+            "Only one integral sequence supported. Instead got `2`."
+        )
+
         rf_slice = format.reformat_slices(slice(None))
         self.assertEqual(
             rf_slice,