Hello TurboGears

The fastest way to start using TurboGears is through the minimal mode, when using TurboGears with minimal mode a default setup that minimizes dependencies and complexity is provided.

Note

While minimal mode is well suited for small simple web applications or web services, for more complex projects moving to a package based configuration is suggested. To start with a package based application the 20 Minutes Wiki Tutorial tutorial is provided.

Play with TurboGears

If you want to experiment with this tutorial without installing TurboGears on your local machine, feel free to edit the Basic TurboGears Example on Runnable and skip the Setup section.

This will provide a working TurboGears application in your browser you can freely edit and run.

Setup

First we are going to create a virtual environment where to install the framework, if you want to proceed without using a virtual environment simply skip to Install TurboGears. Keep in mind that using a virtual environment is the suggested way to install TurboGears without messing with your system packages and python modules. To do so we need to install the virtualenv package:

$ pip install virtualenv

Now the virtualenv command should be available and we can create and activate a virtual environment for our TurboGears2 project:

$ virtualenv tgenv
$ . tgenv/bin/activate

If our environment got successfully created and activated we should end up with a prompt that looks like:

(tgenv)$

Now we are ready to install TurboGears itself:

(tgenv)$ pip install  TurboGears2

Hello World

A TurboGears application consists of an AppConfig application configuration and an application RootController. The first is used to setup and create the application itself, while the latter is used to dispatch requests and take actions.

For our first application we are going to define a controller with an index method that just tells Hello World:

from tg import expose, TGController, AppConfig

class RootController(TGController):
    @expose()
    def index(self):
        return 'Hello World'

now to make TurboGears serve our controller we must create the actual application from an AppConfig:

config = AppConfig(minimal=True, root_controller=RootController())

application = config.make_wsgi_app()

then we must actually serve the application:

from wsgiref.simple_server import make_server

print "Serving on port 8080..."
httpd = make_server('', 8080, application)
httpd.serve_forever()

Running the Python module just created will start a server on port 8080 with the our hello world application, opening your browser and pointing it to http://localhost:8080 should present you with an Hello World text.

Serving Multiple Pages

Now that we have a working application it’s time to say hello to our user instead of greeting the world, to do so we can extend our controller with an hello method which gets as a parameter the person to greet:

class RootController(TGController):
    @expose()
    def index(self):
        return 'Hello World'

    @expose()
    def hello(self, person):
        return 'Hello %s' % person

Restarting the application and pointing the browser to http://localhost:8080/hello?person=MyName should greet you with an Hello MyName text.

Note

How and why requests are routed to the index and hello methods is explained in Object Dispatch documentation

Passing parameters to your controllers is as simple as adding them to the url with the same name of the parameters in your method, TurboGears will automatically map them to function arguments when calling an exposed method.

Serving Templates

Being able to serve text isn’t usually enough for a web application, for more advanced output using a template is usually preferred. Before being able to serve a template we need to install a template engine and enable it.

The template engine we are going to use for this example is Jinja2 which is a fast and flexible template engine with python3 support. To install jinja simply run:

(tgenv)$ pip install jinja2

Now that the template engine is available we need to enable it in TurboGears, doing so is as simple as adding it to the list of the available engines inside our AppConfig:

config = AppConfig(minimal=True, root_controller=RootController())
config.renderers = ['jinja']

application = config.make_wsgi_app()

Now our application is able to expose templates based on the Jinja template engine, to test them we are going to create an hello.jinja file inside the same directory where our application is available:

<!doctype html>
<title>Hello</title>
{% if person %}
  <h1>Hello {{ person }}</h1>
{% else %}
  <h1>Hello World!</h1>
{% endif %}

then the hello method will be changed to display the newly created template instead of using a string directly:

class RootController(TGController):
    @expose()
    def index(self):
        return 'Hello World'

    @expose('hello.jinja')
    def hello(self, person=None):
        return dict(person=person)

Restarting the application and pointing the browser to http://localhost:8080/hello or http://localhost:8080/hello?person=MyName will display an hello page greeting the person whose name is passed as parameter or the world itself if the parameter is missing.

Enabling Helpers

Helpers are python functions which render small HTML snippets that can be useful in your templates. This might include your user avatar, a proper date formatter or whatever might come in hand in your templates. Those are usually provided by turbogears with the h name inside all your templates.

TurboGears2 usually provides the WebHelpers2 package in applications quickstarted in full stack mode, but this can be easily made available in minimal mode too.

First we are going to install the WebHelpers2 package:

$ pip install webhelpers2

Then we are going to import webhelpers2 and register it in our configuration as the application helpers (any python module or object can be registered as the helpers):

import webhelpers2
import webhelpers2.text
config['helpers'] = webhelpers2

Now the helpers are available in all our templates as h.helpername and in this case we are going to use the text.truncate helper to truncate strings longer than 5 characters in our hello.jinja template:

<!doctype html>
<title>Hello</title>
{% if person %}
  <h1>Hello {{ h.text.truncate(person, 5) }}</h1>
{% else %}
  <h1>Hello World!</h1>
{% endif %}

By restarting the application you will notice that pointing the browser to http://localhost:8080/hello?person=World prints Hello World while pointing it to http://localhost:8080/hello?person=TurboGears will print Hello Tu... as TurboGears is now properly truncated.

Serving Static Files

Even for small web applications being able to apply style through CSS or serving javascript scripts is often required, to do so we must tell TurboGears to serve our static files and from where to serve them:

config = AppConfig(minimal=True, root_controller=RootController())
config.renderers = ['jinja']
config.serve_static = True
config.paths['static_files'] = 'public'

application = config.make_wsgi_app()

After restating the application, any file placed inside the public directory will be served directly by TurboGears. Supposing you have a style.css file you can access it as http://localhost:8080/style.css.

Working With Database

TurboGears2 supports both SQL dbms through SQLAlchemy and MongoDB through Ming, both can be enabled with some options and by providing a Model for the application.

The following will cover how to work with SQLAlchemy and extend the sample application to log and retrieve a list of greeted people. First we will need to enable SQLAlchemy support for our application:

config['use_sqlalchemy'] = True
config['sqlalchemy.url'] = 'sqlite:///devdata.db'

Now TurboGears will configure a SQLAlchemy engine for us, but it will require that we provide a data model, otherwise it will just crash when starting up. This can be done by providing a database Session and a model initialization function:

from tg.util import Bunch
from sqlalchemy.orm import scoped_session, sessionmaker

DBSession = scoped_session(sessionmaker(autoflush=True, autocommit=False))

def init_model(engine):
    DBSession.configure(bind=engine)

config['model'] = Bunch(
    DBSession=DBSession,
    init_model=init_model
)

This will properly make our application work and able to interact with the database, but it won’t do much as we are not actually declaring any table or model to work with.

Accessing Data

To start working with tables and the data they contain we need to declare the table itself, this can be done through the SQLAlchemy declarative layer by using a Declarative Base class:

from sqlalchemy.ext.declarative import declarative_base

DeclarativeBase = declarative_base()

From this class we can then inherit all our models:

from sqlalchemy import Column, Integer, DateTime, String
from datetime import datetime


class Log(DeclarativeBase):
    __tablename__ = 'logs'

    uid = Column(Integer, primary_key=True)
    timestamp = Column(DateTime, nullable=False, default=datetime.utcnow)
    person = Column(String(50), nullable=False)

This will allow us to read and write rows from the logs table, but before we are able to do so we must ensure that the table actually exists, which can be done by extending our model initialization function to create the tables:

def init_model(engine):
    DBSession.configure(bind=engine)
    DeclarativeBase.metadata.create_all(engine)  # Create tables if they do not exist

Now we can finally extend our controller to log the people we greet and provide us the list of past greetings:

class RootController(TGController):
    @expose(content_type='text/plain')
    def index(self):
        logs = DBSession.query(Log).order_by(Log.timestamp.desc()).all()
        return 'Past Greetings\n' + '\n'.join(['%s - %s' % (l.timestamp, l.person) for l in logs])

    @expose('hello.jinja')
    def hello(self, person=None):
        DBSession.add(Log(person=person or ''))
        DBSession.commit()
        return dict(person=person)

Going Forward

While it is possible to manually enable the TurboGears features like the SQLAlchemy and Ming storage backends, the application helpers, app_globals, i18n features through the AppConfig object, if you need them you probably want to switch to full stack mode and to create a full stack application through the gearbox quickstart command.

The 20 Minutes Wiki Tutorial provides an introduction to more complex applications with all the TurboGears features enabled, follow it if you want to unleash all the features that TurboGears provides!