Updated code for Python 3.

diner.py

@@ -8,7 +8,7 @@ from sqlalchemy.orm import sessionmaker, relationship
 # class that we can use for objects that we want SQLAlchemy to persist in a
 # database.  We then store that class in variable named Persisted; effectively,
 # we make a new class called Persisted.
-Persisted = declarative_base()
+Persisted = declarative_base()  # pylint: disable=invalid-name
 
 
 class Menu(Persisted):
@@ -42,8 +42,7 @@ class OrderItem(Persisted):
 class DinerDatabase(object):
     @staticmethod
     def construct_mysql_url(authority, port, database, username, password):
-        return 'mysql+mysqlconnector://{username}:{password}@{authority}:{port}/{database}' \
-            .format(authority=authority, port=port, database=database, username=username, password=password)
+        return f'mysql+mysqlconnector://{username}:{password}@{authority}:{port}/{database}'
 
     @staticmethod
     def construct_in_memory_url():
@@ -51,7 +50,7 @@ class DinerDatabase(object):
 
     def __init__(self, url):
         self.engine = create_engine(url)  # an engine is like an endpoint, something to connect to
-        self.Session = sessionmaker()  # create a class for connections to that endpoint
+        self.Session = sessionmaker()  # create a class for connections to that endpoint / pylint: disable=invalid-name
         self.Session.configure(bind=self.engine)  # associate the class with the endpoint
 
     def ensure_tables_exist(self):

diner_installer.py

-# -*- coding: utf-8; -*-
-
 from sys import stderr
 
 from sqlalchemy.exc import SQLAlchemyError
@@ -34,7 +32,7 @@ def main():
         print('Records created.')
     except SQLAlchemyError as exception:
         print('Database setup failed!', file=stderr)
-        print('Cause: {exception}'.format(exception=exception), file=stderr)
+        print(f'Cause: {exception}', file=stderr)
         exit(1)