diff --git a/lib/py/src/compat.py b/lib/py/src/compat.py
index 41bcf35..0e8271d 100644
--- a/lib/py/src/compat.py
+++ b/lib/py/src/compat.py
@@ -29,6 +29,9 @@
     def str_to_binary(str_val):
         return str_val
 
+    def byte_index(bytes_val, i):
+        return ord(bytes_val[i])
+
 else:
 
     from io import BytesIO as BufferIO  # noqa
@@ -38,3 +41,6 @@
 
     def str_to_binary(str_val):
         return bytes(str_val, 'utf8')
+
+    def byte_index(bytes_val, i):
+        return bytes_val[i]