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Design

Following is a quick overview of the design of our wiki application, to help us understand the changes that we will be making as we work through the tutorial.

Overall

We choose to use reStructuredText markup in the wiki text. Translation from reStructuredText to HTML is provided by the widely used docutils Python module. We will add this module in the dependency list on the project setup.py file.

Models

We’ll be using a SQLite database to hold our wiki data, and we’ll be using SQLAlchemy to access the data in this database.

Within the database, we define a single table named pages, whose elements will store the wiki pages. There are two columns: name and data.

URLs like /PageName will try to find an element in the table that has a corresponding name.

To add a page to the wiki, a new row is created and the text is stored in data.

A page named FrontPage containing the text This is the front page, will be created when the storage is initialized, and will be used as the wiki home page.

Views

There will be three views to handle the normal operations of adding, editing and viewing wiki pages, plus one view for the wiki front page. Two templates will be used, one for viewing, and one for both for adding and editing wiki pages.

The default templating systems in Pyramid are Chameleon and Mako. Chameleon is a variant of ZPT, which is an XML-based templating language. Mako is a non-XML-based templating language. Because we had to pick one, we chose Chameleon for this tutorial.

Security

We’ll eventually be adding security to our application. The components we’ll use to do this are below.

  • USERS, a dictionary mapping users names to their corresponding passwords.

  • GROUPS, a dictionary mapping user names to a list of groups they belong to.

  • groupfinder, an authorization callback that looks up USERS and GROUPS. It will be provided in a new security.py file.

  • An ACL is attached to the root resource. Each row below details an ACE:

    Action Principal Permission
    Allow Everyone View
    Allow group:editors Edit
  • Permission declarations are added to the views to assert the security policies as each request is handled.

Two additional views and one template will handle the login and logout tasks.

Summary

The URL, actions, template and permission associated to each view are listed in the following table:

URL Action View Template Permission
/ Redirect to /FrontPage view_wiki    
/PageName Display existing page [2] view_page [1] view.pt view
/PageName/edit_page

Display edit form with existing content.

If the form was submitted, redirect to /PageName

edit_page edit.pt edit
/add_page/PageName

Create the page PageName in storage, display the edit form without content.

If the form was submitted, redirect to /PageName

add_page edit.pt edit
/login
Display login form,
Forbidden [3]

If the form was submitted, authenticate.

  • If authentication successful, redirect to the page that we came from.
  • If authentication fails, display login form with “login failed” message.
login login.pt  
/logout Redirect to /FrontPage logout    
[1]This is the default view for a Page context when there is no view name.
[2]Pyramid will return a default 404 Not Found page if the page PageName does not exist yet.
[3]pyramid.exceptions.Forbidden is reached when a user tries to invoke a view that is not authorized by the authorization policy.

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