TL;DR: You have to write an exception view in file system code which is rendered when an exception occurs.
If an exception occurred in Zope 2 the
standard_error_message (an object in the ZODB) was rendered. This way the error page could be customised through the web.
When using a WSGI server on Zope 2 the
standard_error_message is no longer used. The exceptions have to be handled in a WSGI middleware. (This is a sub-optimal solution as the middleware is not run in the same execution context where the exception occurred.)
Thats why error handling changed again in Zope 4: Like Zope 3 (aka BlueBream) Zope 4 tries to lookup an exception view if an exception occurs. If the lookup succeeds (aka there is an exception view registered for the current exception) this view is rendered as response. This approach allows different views for different exceptions. The
standard_error_message is even gone when installing Zope 4 from scratch.
The exception view has to be created in the file system and registered via ZCML. If you do not have a file system package yet – where this code can be placed – you can create a new package e. g. by using
$ bin/pip install PasteScript $ bin/paster create -t basic_package errorviews $ bin/pip install -e errorviews
errorviews is the name of my example package.
In the existing
errorviews/__init__.pyenter the following code:
class SiteErrorView(object): """View rendered on SiteError.""" def __call__(self): return "SiteError!"
This view returns the string
SiteError! instead of the standard error message. It has to be registered via ZCML. Write a file named
configure.zcml right besides
<configure xmlns="http://namespaces.zope.org/zope" xmlns:browser="http://namespaces.zope.org/browser"> <browser:page for="Exception" name="index.html" class=".SiteErrorView" permission="zope.Public" /> </configure>
The view gets registered for
Exception and all classes inheriting from it. (This might be a bit too general for use in actual code, I know.) Zope 4 expects that the name is
class is a relative dotted path to the view class.
If you put these files into a Zope Product they could be picked automatically. If you created an
errorviews package like me you have to register it in
etc/site.zcml . Put the following line near the end before
<include package="errorviews" />
After re-starting Zope each exception renders as
Using a PageTemplate
Writing HTML in a Python class is not very convenient. It is easier to use a PageTemplate to store the templating code. Create a file
error.pt right beside
<html> <body> <h1>SiteError occurred</h1> </body> </html>
template="error.pt". (The view class is not used in this example.) After re-starting Zope each exception renders the HTML page.
If you have an existing
Data.fs and want to re-use
standard_error_message you might try the following hack: Change
configure.zcml (back) to the XML code shown in the section “Base solution”. Change
__init__.py to the following content:
class SiteErrorView(object): """View rendered on SiteError.""" def __call__(self): root = self.request['PARENTS'][-1] return root.standard_error_message( error_type=self.context.__class__.__name__, error_value=str(self.context))
The code in the example expects that
standard_error_message is a
DTMLMethod (as provided by Zope 2.13). The arguments
error_value allow using
&dtml-error_value; in the
DTMLMethod as before.
Zope 4 has a nice and flexible concept to render error pages. But it requires at least some Python code in the file system. Even this can be tricked back to
standard_error_message if needed. But I think this should only be used for old applications or as an interim solution.