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Understanding URL Handling

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Problem: how to design a url handling / dispatching scheme for the entire site


web.py’s URL handling scheme is simple yet powerful and flexible. at the top of each application, you usually see the full URL dispatching scheme defined as a tuple:

urls = (
    "/tasks/?", "signin",
    "/tasks/list", "listing",
    "/tasks/post", "post",
    "/tasks/chgpass", "chgpass",
    "/tasks/act", "actions",
    "/tasks/logout", "logout",
    "/tasks/signup", "signup"

The format of this tuple is: url-path-pattern, handler-class this pattern will repeat as more url patterns are defined. If you don’t understand the relationship between url pattern and handler classes, please read the Hello World example or Quick Start Tutorial before reading any other cookbook recipes.

Path Matching

You can utilize the power of regular expressions to design more flexible url patterns. For example, /(test1 test2) will catch either /test1 or /test2. The key point to understand is that this matching happens on the path of your URL. For example, the following URL:

The path of this URL is /myapp/greetings/hello. web.py will internally add ^ and $ to the url pattern so that the pattern /tasks/ will not match /tasks/addnew. As it matches against the path, you can not use a pattern like: /tasks/delete?name=(.+) as the part after ? is called query and is not matched against. For a detailed description of URL components, please read web.ctx.

Capture Parameters

In the url pattern you can catch parameters which can be used in your handler class:

"/users/list/(.+)", "list_users"

The chunk after list/ are captured and can be used as a parameter in GET or POST:

class list_users:
    def GET(self, name):
        return "Listing info about user: {0}".format(name)

You can define more than one parameters as you wish. Also note that URL query parameters (which appears after the ?) can be obtained using web.input()

Note on sub-applications

To better handle larger web applications, web.py support sub-applications. While designing url scheme with sub applications, keep in mind that the path (web.ctx.path) will get the parent path stripped off. e.g. if in the main application, you define to forward url pattern “/blog” to the ‘blog’ sub-application, in your blog sub-application all url patterns starts with “/”, not /blog. Read the web.ctx cookbook recipe for more details.