Python References

Many places in the configuration take optional pyref attributes. These reference a module/function name.

The general pattern is:


The location can be a module name, or file:/path/to/ If it is a literal filename, then the file is exec’d and turned into a module that way. All references are to functions (or callable objects), and so you must give the function name. Note that the file: case isn’t a URL, just a path.


You can pass extra ad hoc arguments to the function using attributes in this form. This would add the keyword argument foo="bar" to the function call. All arguments have string (well, unicode) values.

In addition to the ad-hoc arguments, parameters such as the request and response, and a logger, will be passed into your pyref functions. The particular parameters passed in vary for each case, as do the expected return values. See below for details.

When they are available, request and response are WebOb objects and log is a Python logging object.



A <theme pyref> replaces a <theme href> and so your pyref function should return a string href.

You can use a <theme> like:

<theme pyref="mymodule:get_theme" />

Then define a function like:

def get_theme(request, response, log):
    return "/%s/theme.html" %

request is the original request received by Deliverance.

response is the content HTTP response, i.e. the current page to be themed. Note that this allows you to point to different theme locations based on conditions of the current page, by inspecting response‘s status code, headers or even body.

You can raise AbortTheme in this function (or anywhere else) to signal that the response should be returned without any theme applied.


Within a <proxy> tag, you can use a <dest pyref> to dynamically generate the proxy destination from code. Your pyref function should return a URL. For example:

<proxy path="/trac">
  <dest pyref="mymodule:get_proxy_dest" />

with the function:

def get_proxy_dest(request, log):
    if not request.remote_addr.startswith('192'):
        raise AbortProxy('Bad remote_addr: %r' % request.remote_addr)
    return 'http://localhost:10002'

You can return any URL. URI template substitution is not performed.

If you raise AbortProxy then the <proxy> will be skipped, and another proxy will be looked for. (If nothing matches a 404 error is returned.)


Within a <proxy> tag, you can use a <request pyref> to arbitrarily modify or replace the request object before the proxying occurs.

Your pyref function must return a webob.Request object. For example:

<request pyref="mymodule:modify_proxy_request" />

with the code:

def modify_proxy_request(request, log):
    request.header['X-Project-Name'] ='.')[0]
    return request

Note that you can modify the request in-place or return a new request.


Within a <proxy> tag you can use a <response pyref> to arbitrarily modify or replace the response object returned by the proxy, before theming occurs.

Your pyref function will receive six arguments (and any custom keyword arguments you define) – the signature is (request, response, orig_base, proxied_base, proxied_url, log):

Since request is a webob.Request object, you can get the full original URL from request.url, and all headers.

Your pyref function must return a webob.Response object. For example:

<response pyref="mymodule:modify_proxy_response" />

with the code:

def modify_proxy_response(request, response,
                          orig_base, proxied_base, proxied_url, log):
    response.body += 'look at me!'
    return response

Note that you can modify the response in place or return a new webob.Response.

Match, rule, proxy

The <match>, <rule> and <proxy> elements all support a pyref attribute to determine whether they should be active for the current request.

Your pyref function should return a boolean.

The signature is (request, response, response_headers, log):

  • response: the current response object, if applicable.
  • response_headers: a list of all the headers in the response, if applicable, including <meta http-equiv> headers.

In <proxy> elements, response and response_headers will be None, because <proxy> commands occur before any subrequest is made.

An example:

def match_request(request, response, response_headers, log):
    if response.headers.get('x-notheme'):
        raise AbortTheme
    return True


You can disallow Python references using deliverance-proxy with: