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The TurboGears 2 Wiki Tutorial

Welcome! This tutorial will show you how to create a simple wiki with TurboGears 2. It is designed to be your first experience with TurboGears 2.

If you're not familiar with wikis, you might want to check out the Wikipedia entry. Basically, a wiki is an easily-editable collaborative web content system that makes it trivial to link to pages and create new pages.

If you have trouble with this tutorial, ask for help on the TurboGears discussion list. We're a friendly bunch and depending what time of day you post, you'll get your answer in a few minutes to a few hours. If you search the mailing list or the web in general, you'll probably get your answer even faster. Please don't post your problem reports as comments on this or any of the following pages of the tutorial. Comments are for suggestions for improvement of the docs etc., not for seeking support.

Setup

To go through this tutorial, you'll need:

  1. Python 2.4 or 2.5. Note that Mac OSX 10.5 (Leopard) comes with Python 2.5 preinstalled; for 10.4 and before, follow Macintosh in the above link.

  2. TurboGears 2.0 or higher.

  3. docutils 0.4 or later, which is used for the wiki's formatting. docutils is not a required part of TurboGears, but is needed for this tutorial. Install it with:

    $ easy_install docutils
    

    When using easy_install, it doesn't matter what directory you're in. If you don't have easy_install, you only need to run http://peak.telecommunity.com/dist/ez_setup.py from any directory.

  4. A web browser.

  5. Your favorite editor.

  6. Two command line windows (you only need one, but two is nicer).

  7. A database. Python 2.5 comes sqlite, so if you have Python 2.5, don't do anything. If you're running Python 2.4, your best bet is sqlite 3.2+ with pysqlite 2.0+. Install it with:

    $ easy_install pysqlite
    
  8. Optional: If you're not aware of it, you may also find the ipython shell to be helpful. It supports attribute tab completion for many objects (which can help you find the method you're searching for) and can display contextual help if you append a question mark onto the end of an object or method. You can do the same in the standard shell with the dir() and help() functions, but ipython is more convenient. ipython has a number of other convenient features, like dropping into the debugger on an error; take a look at the ipython docs for more information. You can install it with:

    $ easy_install ipython
    

This tutorial doesn't cover Python at all. Check the Python Documentation page for more coverage of Python.

Quickstart

TurboGears provides a suite of tools for working with projects by adding several commands to the Python command line tool paster. A few will be touched upon in this tutorial. (Check the command line reference for a full listing.) The first tool you'll need is quickstart, which initializes a TurboGears project. Go to one of your command line windows and run the following command:

$ paster quickstart

You'll be prompted for the name of the project (this is the pretty name that human beings would appreciate), and the name of the package (this is the less-pretty name that Python will like). Here's what our choices for this tutorial look like:

$ paster quickstart
Enter project name: Wiki 20
Enter package name [wiki20]: wiki20
Do you need authentication and authorization in this project? [yes] no

Now paster will spit out a bunch of stuff:

Selected and implied templates:
  TurboGears2#turbogears2
  TurboGears 2.0 Template

...etc...

running compile_catalog
1 of 1 messages (100%) translated in 'wiki20/i18n/ru/LC_MESSAGES/wiki20.po'
compiling catalog 'wiki20/i18n/ru/LC_MESSAGES/wiki20.po' to 'wiki20/i18n/ru/LC_MESSAGES/wiki20.mo'

This creates a few files in a directory tree just below your current directory. Go in there and take a look around:

$ cd Wiki-20

paster provides a simple mechanism for running a TurboGears project. From inside the Wiki-20 directory, run this command:

$ paster serve --reload development.ini

(You'll get a warning that starts with No handlers could be found for logger "toscawidgets.view", but that's OK; your system will still run.)

The --reload flag means that changes that you make in the project will automatically cause the server to restart itself. This way you immediately see the results.

Point your browser at http://localhost:8080/, and you'll see a nice welcome page. You now have a working project!

Controller and View

If you take a look at the code that quickstart created, you'll see everything necessary to get up and running. Here, we'll look at the two files directly involved in displaying this welcome page.

TurboGears follows the Model-View-Controller paradigm (a.k.a. "MVC"), as do most modern web frameworks like Rails, Cake, Struts, etc.

  • Model: For a web application, the "model" refers to the way the data is stored. In theory, any object can be your model. In practice, since we're in a database-driven world, your model will be based on a relational database. By default, TurboGears 2 uses the powerful, flexible, and relatively easy-to-use SQLAlchemy object relational mapper to build your model, and to talk to your database. We'll look at this in a later section.
  • View: To minimize duplication of effort, web frameworks use templating engines which allow you to create "template" files to specify how a page will always look, with hooks where the templating engine can substitute information provided by your web application. TurboGears 2's default templating engine is Genshi. If you really love another templating engine, there are plugins available for most popular Python templating engines. See the using alternate templating engines article for details.
  • Controller: The controller is the way that you tell your web application how to respond to events that arrive on the server. In a web application, an "event" usually means "visiting a page" or "pressing a submit button," and the response to an event usually consists of executing some code and displaying a new page. TurboGears 2 uses its own simple controller.

Controller Code

Wiki-20/wiki20/controllers/root.py is the code that causes the welcome page to be produced. After the imports, the first line of code creates our main controller class by inheriting from TurboGears' BaseController:

class RootController(BaseController):

The TurboGears 2 controller is a simple object publishing system; you write controller methods and @expose() them to the web. In our case, there's a single controller method called index. As you might guess, this name is not accidental; this becomes the default page you'll get if you go to this URL without specifying a particular destination, just like you'll end up at index.html on an ordinary web server if you don't give a specific file name. You'll also go to this page if you explicitly name it, with http://localhost:8080/index. (We'll see other controller methods later in the tutorial so this naming system will become clear).

The @expose() decorator tells TurboGears which template to use to render the page. Our @expose() specifies:

@expose('wiki20.templates.index')

This gives the file name to use, including the path information (the .html extension is implied). We'll look at this file shortly.

The flash() function is a simple way to show a message.

Each controller method returns a dictionary, as you can see at the end of index. TG takes the key:value pairs in this dictionary and turns them into local variables that can be used in the template.

Displaying the Page

Wiki-20/wiki20/templates/index.html is the template specified by the @expose() decorator, so it formats what you view on the welcome screen. Look at the file; you'll see that it's standard XHTML with some simple namespaced attributes. This makes it very designer-friendly, and well-behaved design tools will respect all the Genshi tags. You can even open it directly in your browser.

Genshi directives are usually found within div or span tags, and begin with the py: namespace. Each one represents a python block of code, but instead of ending with the outdent as in python, the end of the tag represents the end of the block. Look through the index.html file to see the Genshi directives.

Next, we'll set up our data model, and create a database.

Wiki Model and Database

quickstart produced a directory for our model in Wiki-20/wiki20/model/. This directory contains an __init__.py file, which makes that directory name into a python module (so you can say import model).

In order to easily use our model within the application, modify the Wiki-20/wiki20/model/__init__.py file to add Page and pages_table to the module. Add the following line at the end of the file. It's very important that this line is at the end because of some initialization ordering issues:

Since a wiki is basically a linked collection of pages, we'll define a Page class as the name of our model. Create a new file called page.py in the Wiki-20/wiki20/model/ directory:

The MetaData object is automatically created by the paste command inside the __init__.py file. It's a "single point of truth" that keeps all the information necessary to connect and use the database. It includes the location of the database, connection information, and the tables that are in that database. When you pass the metadata object to the various objects in your project they initialize themselves using that metadata.

In this case, the metadata object configures itself using the development.ini file, which we'll look at in the next section.

The SQLAlchemy Table object defines what a single table looks like in the database, and adds any necessary constraints (so, for example, even if your database doesn't enforce uniqueness, SQLAlchemy will attempt to do so). The first argument in the Table constructor is the name of that table inside the database. Next is the aforementioned metadata object followed by the definitions for each Column object. As you can see, Column objects are defined in the same way that you define them within a database: name, type, and constraints.

The Table object provides the representation of a database table, but we want to just work with objects, so we create an extremely simple class to represent our objects within TurboGears. The above idiom is quite common: you create a very simple class like Page with nothing in it, and add all the interesting stuff using mapper(), which attaches the Table object to our class.

Note that it's also possible to start with an existing database, but that's a more advanced topic that we won't cover in this tutorial.

Database Configuration

By default, projects created with quickstart are configured to use a very simple SQLite database (however, TurboGears 2 supports most popular databases). This configuration is controlled by the development.ini file in the root directory (Wiki-20, for our project).

Search down until you find the [app:main] section in development.ini, and then look for sqlalchemy.url. You should see this:

sqlalchemy.url = sqlite:///%(here)s/devdata.db

Turbogears will automatically replace the %(here)s variable with the parent directory of this file, so for our example it will produce sqlite:///Wiki-20/devdata.db. You won't see the devdata.db file now because we haven't yet initialized the database.

Initializing the Tables

Before you can use your database, you need to initialize it and add some data. There's some built in support for this in TurboGears, but one of the easiest ways to do this is just to run a standard Python script. Create a file called initializeDB.py in the Wiki-20 directory containing the following:

If you're familiar with SQLAlchemy this should look pretty standard to you. The only part that's different is that we use:

transaction.commit()

where you're used to seeing Session.commit() we use transaction.commit this calls the transaction manager which helps us to support cross database transactions, as well as transactions in non relational databases, but ultimately in the case of SQLAlchemy it calls Session.commit() just like might if you were doing it directly.

Now run the program from the Wiki-20 directory:

$ python initializeDB.py

You'll see output, but you should not see error messages. At this point your database is created and has some initial data in it, which you can verify by looking at Wiki-20/devdata.db. The file should exist and have a nonzero size.

That takes care of the "M" in MVC. Next is the "C": controllers.

Adding Controllers

Controllers are the code that figures out which page to display, what data to grab from the model, how to process it, and finally hands off that processed data to a template.

quickstart has already created some basic controller code for us at Wiki-20/wiki20/controllers/root.py. Here's what it looks like now:

The first thing we need to do is uncomment the line that imports DBSession.

Next we must import the Page class from our model. At the end of the import block, add this line:

from wiki20.model.page import Page

Now we will change the template used to present the data, by changing the @expose line:

@expose('wiki20.templates.page')

This requires us to create a new template named page.html in the wiki20/templates directory; we'll do this in the next section.

Now we must specify which page we want to see. To do this, add a parameter to the index() method. Change the line after the @expose decorator to:

def index(self, pagename="FrontPage"):

This tells the index() method to accept a parameter called pagename, with a default value of "FrontPage".

Now let's get that page from our data model. Put this line in the body of index:

page = DBSession.query(Page).filter_by(pagename=pagename).one()

This line asks the current SQLAlchemy in-memory database session object to run a query for records with a pagename column equal to the value of the pagename parameter passed to our controller method. The .one() method assures that there is only one returned result; normally a .query call returns a list of matching objects. We only want one page, so we use .one().

Finally, we need to return a dictionary containing the page we just looked up. When we say:

return dict(wikipage=page)

The returned dict contains a single key called page and a single value containing the page that we looked up.

Here's the whole file after incorporating the above modifications:

Now our index() method fetches a record from the database (creating an instance of our mapped Page class along the way), and returns it to the template within a dictionary.

Feel free to comment out (or remove) the flash() call too, to tidy the output up a bit.

Adding Views (Templates)

quickstart also created some templates for us in the Wiki-20/wiki20/templates directory: master.html and index.html. Back in our simple controller, we used @expose() to hand off a dictionary of data to a template called 'wiki20.templates.index', which corresponds to Wiki-20/wiki20/templates/index.html.

Take a look at the following line in index.html:

<xi:include href="master.html" />

This tells the index template to include the master template. Using includes lets you easily maintain a cohesive look and feel throughout your site by having each page include a common master template.

Similarly the lines:

<xi:include href="header.html" />
<xi:include href="footer.html" />

Tell genshi to suck in the headers and footers for the page.

Copy index.html into a file called page.html. Now modify it for our purposes:

This is a basic XHTML page with three substitutions:

  1. In the <title> tag, we substitute the name of the page, using the pagename value of page. (Remember, wikipage is an instance of our mapped Page class, which was passed in a dictionary by our controller.)

  2. In the second <div> element, we substitute the page name again with Genshi's py:replace:

  3. In the third <div>, we put in the contents of our wikipage:

When you refresh the output web page you should see "initial data" displayed on the page.

Editing pages

One of the fundamental features of a wiki is the ability to edit the page just by clicking "Edit This Page," so we'll create a template for editing. First, make a copy of page.html:

cd wiki20/templates
cp page.html edit.html
cd ../..

We need to replace the content with an editing form and ensure people know this is an editing page. Here are the changes for edit.html.

  1. Change the title in the header to reflect that we are editing the page:

  2. Change the div that displays the page:

    with a div that contains a standard HTML form:

Now that we have our view, we need to update our controller in order to display the form and handle the form submission. For displaying the form, we'll add an edit method to our controller in Wiki-20/wiki20/controllers/root.py. The new root.py file looks like this:

For now, the new method is identical to the index method; the only difference is that the resulting dictionary is handed to the edit template. To see it work, go to http://localhost:8080/edit/FrontPage. However, this only works because FrontPage already exists in our database; if you try to edit a new page with a different name it will fail, which we'll fix in a later section.

Don't click that save button yet! We still need to write that method.

Saving our edits

When we displayed our wiki's edit form in the last section, the form's action was /save. So, we need to make a method called save in the Root class of our controller.

However, we're also going to make another important change. Our index method is only called when you either go to / or /index. If you change the index method to the special method default, then default will be automatically called whenever nothing else matches. default will take the rest of the URL and turn it into positional parameters.

Here's our new version of root.py which includes both default and save:

Unlike the previous methods we've made, save just uses a plain @expose() without any template specified. That's because we're only redirecting the user back to the viewing page.

Although the page.data = data statement tells SQLAlchemy that you intend to store the page data in the database, nothing happens until the DBSession.flush() method is called. This is commonly refered to as the "unit of work" pattern, and it's an important structure for database developers because it allows SQLAlchemy to combine many operations into a single database update (or a minimized number of updates if some changes depend upon earlier changes) and thus be much more efficient in the database resources used.

SQLALchemy also provides a ``DBSession.commit() method which flushes and commits any changes you've made in a trasaction. TurboGears 2 provides a flexible transaction management system that automates this process wrapping each web request in it's own transaction and automatically rolling back that transaction if you get a python exception, or return an HTTP error code as your response.

You don't have to do anything to use this transaction management system, it should just work. So, you can now make changes and save the page we were editing, just like a real wiki.

What about WikiWords?

Our wiki doesn't yet have a way to link pages. A typical wiki will automatically create links for WikiWords when it finds them (WikiWords have also been described as WordsSmashedTogether). This sounds like a job for a regular expression.

Here's the new version of root.py, which will be explained afterwards:

We need some additional imports, including re for regular expressions and a method called publish_parts from docutils.

A WikiWord is a word that starts with an uppercase letter, has a collection of lowercase letters and numbers followed by another uppercase letter and more letters and numbers. The wikiwords regular expression describes a WikiWord.

In default, the new lines begin with the use of publish_parts, which is a utility that takes string input and returns a dictionary of document parts after performing conversions; in our case, the conversion is from Restructured Text to HTML. The input (page.data) is in Restructured Text format, and the output format (specified by writer_name="html") is in HTML. Selecting the fragment part produces the document without the document title, subtitle, docinfo, header, and footer.

You can configure TurboGears so that it doesn't live at the root of a site, so you can combine multiple TurboGears apps on a single server. Using tg.url() creates relative links, so that your links will continue to work regardless of how many apps you're running.

The next line rewrites the content by finding any WikiWords and substituting hyperlinks for those WikiWords. That way when you click on a WikiWord, it will take you to that page. The r'string' means 'raw string', one that turns off escaping, which is mostly used in regular expression strings to prevent you from having to double escape slashes. The substitution may look a bit weird, but is more understandable if you recognize that the %s gets substituted with root, then the substitution is done which replaces the \1 with the string matching the regex.

Note that default() is now returning a dict containing an additional key-value pair: content=content. This will not break wiki20.templates.page because that page is only looking for page in the dictionary, however if we want to do something interesting with the new key-value pair we'll need to edit wiki20.templates.page:

Since content comes through as XML, we can strip it off using the XML() function to produce plain text (try removing the function call to see what happens).

To test the new version of the system, edit the data in your front page to include a WikiWord. When the page is displayed, you'll see that it's now a link. You probably won't be surprised to find that clicking that link produces an error.

Hey, where's the page?

What if a Wiki page doesn't exist? We'll take a simple approach: if the page doesn't exist, you get an edit page to use to create it.

In the default method, we'll check to see if the page exists. If it doesn't, we'll redirect to a new notfound method. We'll add this method after the index method and before the edit method. Here are the changes we make to the controller:

The default code changes illustrate the "better to beg forgiveness than ask permission" pattern which is favored by most Pythonistas -- we first try to get the page and then deal with the exception by redirecting to a method that will make a new page.

We're also leaking a bit of our model into our controller. For a larger project, we might create a facade in the model, but here we'll favor simplicity. Notice that we can use the redirect() to pass parameters into the destination method.

As for the notfound method, the first 5 lines of the method adds a row to the page table. From there, the path is exactly the same it would be for our edit method.

With these changes in place, we have a fully functional wiki. Give it a try! You should be able to create new pages now.

Adding a page list

Most wikis have a feature that lets you view an index of the pages. To add one, we'll start with a new template, pagelist.html. We'll copy page.html so that we don't have to write the boilerplate.

cd wiki20/templates
cp page.html pagelist.html

After editing, our pagelist.html looks like:

The bolded section represents the Genshi code of interest. You can guess that the py:for is a python for loop, modified to fit into Genshi's XML. It iterates through each of the pages (which we'll send in via the controller, using a modification you'll see next). For each one, Page Name Here is replaced by pagename, as is the URL. You can learn more about Genshi by following the link at the bottom of this page.

We must also modify the controller to implement pagelist and to create and pass pages to our template:

Here, we select all of the Page objects from the database, and order them by pagename.

We can also modify page.html so that the link to the page list is available on every page:

You can see your pagelist by clicking the link on a page or by going directly to http://localhost:8080/pagelist.

Further Exploration

Now that you have a working Wiki, there are a number of further places to explore:

  1. You can add JSON support via MochiKit.
  2. You can learn more about the Genshi templating engine.
  3. You can learn more about the SQLAlchemy ORM.

If you had any problems with this tutorial, or have ideas on how to make it better, please let us know on the mailing list! Suggestions are almost always incorporated.