Added tradeexcept.py

tradeexcept.py

@@ -0,0 +1,13 @@
+#! /usr/bin/env python
+
+class TradeException(Exception):
+    """
+        Distinguishes runtime logical errors (such as no data for what you
+        queried) from programmatic errors (such as Oliver accessing a hash
+        with the wrong type of key).
+
+        TradeExcepts should be caught by the program and displayed in the
+        most user friendly way possible.
+    """
+    pass
+