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What's new in Zope 4.0

The article explains the new high-level features and changes found in this version of Zope.

You can have a look at the detailed change log to learn about all minor new features and bugs being solved in this release.

Version numbering increase

Version numbers for Zope have been confusing in the past. The original Zope project iterated through version one to two up to version 2.13. In parallel a separate project was launched using the name Zope 3. Zope 3 wasn't a new version of the original Zope project and in hindsight should have used a different project name. These days this effort is known as BlueBream.

In order to avoid confusion between the separate Zope 3 project and a new version of this project, it was decided to skip ahead and use Zope 4.0 as the next version number. The increase in the major part of the version also indicates the number of backwards incompatible changes found in this release.

Python versions

Zope 4 supports both Python 2.7 and Python 3.5 or 3.6. While PyPy is supported by some of the underlying dependencies, it is incompatible with a couple of the foundational C extensions and with RestrictedPython. As a result Zope as a whole is not compatible with PyPy.

The Python 3 support currently covers the core dependencies shipped with Zope and is limited to the new WSGI based publisher. The new external ZServer project is currently limited to Python 2.7 compatibility and likely to stay that way.

Python 3 support is mainly offered for new installations of Zope, as there is so far only an experimental database migration tool in place, see zodb.py3migrate.

Recommended WSGI setup

Zope 2.13 first gained support for running Zope as a WSGI application, using any WSGI capable web server instead of the built-in ZServer.

Zope 4.0 takes this one step further and uses WSGI as the default setup. Functional testing (testbrowser) support also uses the new WSGI publisher.

The ZServer based publisher got moved into its own optional project. So if you rely on ZServer features, like Webdav, FTP, zdaemon or zopectl support, please make sure to install ZServer and use its mkzopeinstance script to create a Zope instance.

The ZServer project also includes limited functional testing support in the ZServer.Testing sub-package. testbrowser support is exclusively available based on the WSGI publisher, as a result of a switch from the unmaintained mechanize project to WebTest.

By default Zope only ships with a new mkwsgiinstance script which creates a Zope instance configured to run as a WSGI application. The example configuration uses the waitress web server, but Zope can be run using any WSGI capable web server.

To make running Zope easier, a new runwsgi command line script got added, which can read a PasteDeploy configuration and create and run the WSGI pipeline specified in it. By default such a configuration is created in the etc/zope.ini file. The runwsgi script supports both -v / --verbose and -d / --debug arguments to print out more information on the console. The debug argument enables Zope's debug mode and disables the catch-all part of the httpexceptions WSGI middleware. This means unexpected and uncaught exceptions show their full traceback on the console and make it easier to debug them. Without debug mode, these exceptions result in a 500 Internal Server Error rendered as a normal HTML response.


In case you experience an HTTP 500: Internal Server Error, where you would expect a Redirect, the following might help you.

Although the zope.ini created by mkwsgiinstance includes egg:Zope#httpexceptions as part of the pipeline, this might not be sufficient for existing projects. In case your project has configured a middleware handling and creating error views for HTTP exceptions, you need to make sure that egg:Zope#httpexceptions runs before that middleware. Otherwise a Redirect might not be handled as such. This can result in a non-functional ZMI.

The WSGI support has no built-in support for running as a daemon. Your chosen WSGI server might support this or you can use external projects like supervisord or systemd.

The WSGI support in Zope 4 has changed in a number of ways to make it more similar to its ZServer equivalent. In Zope 2.13 the WSGI support required using repoze WSGI middlewares to add transaction and retry handling. The WSGI support in Zope 4 no longer supports those middlewares but integrates transaction and retry handling back into the publisher code. This allows it to also add back full support for publication events and exception views. It does mean that the transaction is begun and committed or aborted inside the publisher code and you can no longer write WSGI middlewares that take part in the transaction cycle, but instead have to use Zope specific hooks like you do in the ZServer based publisher.

View components without Acquisition

In Zope 2.12 Zope Toolkit view components changed and stopped inheriting from Acquisition base classes, as Acquisition got aware of __parent__ pointers, which meant that aq_parent(view) worked, without the view having to mix-in an Acquisition base class. For backwards compatibility a new AcqusitionBBB class was mixed in, to continue to support calling view.aq_parent. This backwards compatibility class has been removed in Zope 4, so view.aq_parent no longer works and you have to use aq_parent(view). The same applies for other view components like view page template files or viewlets.

Chameleon based page templates

Chameleon is an alternative implementation of the page template language supporting additional features and impressive template rendering speed.

So far it was available via the project. In Zope 4 the code from has been merged into Zope core and the Chameleon based engine is now the default, removing the need to install manually.

Memory use

Zope 4 depends on a new DateTime release. The new release has been optimized for better memory use. Applications using a lot of DateTime values like the Plone CMS have seen total memory usage to decrease by 10% to 20% for medium to large deployments.

ZMI overhaul

The ZMI (Zope Management Interface) is now styled with Bootstrap. See :ref:`ZMI-label` for details how to adapt Zope add-on packages to the new styling.

Unified encoding

As it is reasonable to have one unified encoding in ZMI and frontend, management_page_charset (as property of a folder) and default-zpublisher- encoding in zope.conf have to define the same encoding, which is utf-8 by default for both.