make Python 3.4 compatible, also restore requirement for a non-empty primary key

Author: dimitri-yatsenko

datajoint/declare.py

@@ -275,6 +275,10 @@ def declare(full_table_name, definition, context):
 
     table_comment, primary_key, attribute_sql, foreign_key_sql, index_sql, external_stores = prepare_declare(
         definition, context)
+
+    if not primary_key:
+        raise DataJointError('Table must have a primary key')
+
     return (
         'CREATE TABLE IF NOT EXISTS %s (\n' % full_table_name +
         ',\n'.join(attribute_sql + ['PRIMARY KEY (`' + '`,`'.join(primary_key) + '`)'] + foreign_key_sql + index_sql) +

datajoint/errors.py

@@ -14,7 +14,7 @@ def suggest(self, *args):
         :param args: addition arguments
         :return: a new exception of the same type with the additional arguments
         """
-        return self.__class__(*self.args, *args)
+        return self.__class__(*(self.args + args))
 
 
 # --- Second Level ---

tests/__init__.py

@@ -116,7 +116,7 @@ def setup_package():
     db_name = "djtest_blob_migrate"
     db_file = "v0_11.sql"
     conn_root.query("""
-        CREATE DATABASE {};
+        CREATE DATABASE IF NOT EXISTS {};
         """.format(db_name))
 
     statements = parse_sql('{}/{}'.format(source, db_file))