Add table_exists() util function

corepos/db/util.py

@@ -36,3 +36,25 @@ def get_last_card_number(session):
     """
     return session.query(sa.func.max(corepos.Customer.card_number))\
                   .scalar() or 0
+
+
+def table_exists(session, model_class):
+    """
+    Determine if a table exists in the database.
+
+    :param session: SQLAlchemy session object, opened against the database in
+       question.
+
+    :param model_class: The model class associated with the table in question.
+
+    :returns: Boolean indicating if the table exists.
+    """
+    try:
+        session.query(model_class).count()
+    except sa.exc.ProgrammingError as error:
+        if "doesn't exist" in str(error):
+            return False
+        else:
+            raise
+    else:
+        return True